Extended Controls
Prev | Chapter 1. Common API Elements | Next

## Extended Controls

### Introduction

The control mechanism as originally designed was meant to be used for user settings (brightness, saturation, etc). However, it turned out to be a very useful model for implementing more complicated driver APIs where each driver implements only a subset of a larger API.

The MPEG encoding API was the driving force behind designing and implementing this extended control mechanism: the MPEG standard is quite large and the currently supported hardware MPEG encoders each only implement a subset of this standard. Further more, many parameters relating to how the video is encoded into an MPEG stream are specific to the MPEG encoding chip since the MPEG standard only defines the format of the resulting MPEG stream, not how the video is actually encoded into that format.

Unfortunately, the original control API lacked some features needed for these new uses and so it was extended into the (not terribly originally named) extended control API.

Even though the MPEG encoding API was the first effort to use the Extended Control API, nowadays there are also other classes of Extended Controls, such as Camera Controls and FM Transmitter Controls. The Extended Controls API as well as all Extended Controls classes are described in the following text.

### The Extended Control API

Three new ioctls are available: `VIDIOC_G_EXT_CTRLS`, `VIDIOC_S_EXT_CTRLS` and `VIDIOC_TRY_EXT_CTRLS`. These ioctls act on arrays of controls (as opposed to the `VIDIOC_G_CTRL` and `VIDIOC_S_CTRL` ioctls that act on a single control). This is needed since it is often required to atomically change several controls at once.

Each of the new ioctls expects a pointer to a struct v4l2_ext_controls. This structure contains a pointer to the control array, a count of the number of controls in that array and a control class. Control classes are used to group similar controls into a single class. For example, control class `V4L2_CTRL_CLASS_USER` contains all user controls (i. e. all controls that can also be set using the old `VIDIOC_S_CTRL` ioctl). Control class `V4L2_CTRL_CLASS_MPEG` contains all controls relating to MPEG encoding, etc.

All controls in the control array must belong to the specified control class. An error is returned if this is not the case.

It is also possible to use an empty control array (count == 0) to check whether the specified control class is supported.

The control array is a struct v4l2_ext_control array. The v4l2_ext_control structure is very similar to struct v4l2_control, except for the fact that it also allows for 64-bit values and pointers to be passed.

It is important to realize that due to the flexibility of controls it is necessary to check whether the control you want to set actually is supported in the driver and what the valid range of values is. So use the `VIDIOC_QUERYCTRL` and `VIDIOC_QUERYMENU` ioctls to check this. Also note that it is possible that some of the menu indices in a control of type `V4L2_CTRL_TYPE_MENU` may not be supported (`VIDIOC_QUERYMENU` will return an error). A good example is the list of supported MPEG audio bitrates. Some drivers only support one or two bitrates, others support a wider range.

All controls use machine endianness.

### Enumerating Extended Controls

The recommended way to enumerate over the extended controls is by using `VIDIOC_QUERYCTRL` in combination with the `V4L2_CTRL_FLAG_NEXT_CTRL` flag:

    struct v4l2_queryctrl qctrl;

    qctrl.id = V4L2_CTRL_FLAG_NEXT_CTRL;
    while (0 == ioctl (fd, VIDIOC_QUERYCTRL, &qctrl)) {
    	/* ... */
    	qctrl.id |= V4L2_CTRL_FLAG_NEXT_CTRL;
    }

The initial control ID is set to 0 ORed with the `V4L2_CTRL_FLAG_NEXT_CTRL` flag. The `VIDIOC_QUERYCTRL` ioctl will return the first control with a higher ID than the specified one. When no such controls are found an error is returned.

If you want to get all controls within a specific control class, then you can set the initial `qctrl.id` value to the control class and add an extra check to break out of the loop when a control of another control class is found:

    qctrl.id = V4L2_CTRL_CLASS_MPEG | V4L2_CTRL_FLAG_NEXT_CTRL;
    while (0 == ioctl (fd, VIDIOC_QUERYCTRL, &qctrl)) {
    	if (V4L2_CTRL_ID2CLASS (qctrl.id) != V4L2_CTRL_CLASS_MPEG)
    		break;
    		/* ... */
    		qctrl.id |= V4L2_CTRL_FLAG_NEXT_CTRL;
    	}

The 32-bit `qctrl.id` value is subdivided into three bit ranges: the top 4 bits are reserved for flags (e. g. `V4L2_CTRL_FLAG_NEXT_CTRL`) and are not actually part of the ID. The remaining 28 bits form the control ID, of which the most significant 12 bits define the control class and the least significant 16 bits identify the control within the control class. It is guaranteed that these last 16 bits are always non-zero for controls. The range of 0x1000 and up are reserved for driver-specific controls. The macro `V4L2_CTRL_ID2CLASS(id)` returns the control class ID based on a control ID.

If the driver does not support extended controls, then `VIDIOC_QUERYCTRL` will fail when used in combination with `V4L2_CTRL_FLAG_NEXT_CTRL`. In that case the old method of enumerating control should be used (see 1.8). But if it is supported, then it is guaranteed to enumerate over all controls, including driver-private controls.

### Creating Control Panels

It is possible to create control panels for a graphical user interface where the user can select the various controls. Basically you will have to iterate over all controls using the method described above. Each control class starts with a control of type `V4L2_CTRL_TYPE_CTRL_CLASS`. `VIDIOC_QUERYCTRL` will return the name of this control class which can be used as the title of a tab page within a control panel.

The flags field of struct v4l2_queryctrl also contains hints on the behavior of the control. See the `VIDIOC_QUERYCTRL` documentation for more details.

### Codec Control Reference

Below all controls within the Codec control class are described. First the generic controls, then controls specific for certain hardware.

Note: These controls are applicable to all codecs and not just MPEG. The defines are prefixed with V4L2_CID_MPEG/V4L2_MPEG as the controls were originally made for MPEG codecs and later extended to cover all encoding formats.

#### Generic Codec Controls

Table 1.2. Codec Control IDs

ID | Type |
| Description
`V4L2_CID_MPEG_CLASS` | class |
| The Codec class descriptor. Calling `VIDIOC_QUERYCTRL` for this control will return a description of this control class. This description can be used as the caption of a Tab page in a GUI, for example.
`V4L2_CID_MPEG_STREAM_TYPE` | enum v4l2_mpeg_stream_type |
| The MPEG-1, -2 or -4 output stream type. One cannot assume anything here. Each hardware MPEG encoder tends to support different subsets of the available MPEG stream types. This control is specific to multiplexed MPEG streams. The currently defined stream types are:

`V4L2_MPEG_STREAM_TYPE_MPEG2_PS` | MPEG-2 program stream
`V4L2_MPEG_STREAM_TYPE_MPEG2_TS` | MPEG-2 transport stream
`V4L2_MPEG_STREAM_TYPE_MPEG1_SS` | MPEG-1 system stream
`V4L2_MPEG_STREAM_TYPE_MPEG2_DVD` | MPEG-2 DVD-compatible stream
`V4L2_MPEG_STREAM_TYPE_MPEG1_VCD` | MPEG-1 VCD-compatible stream
`V4L2_MPEG_STREAM_TYPE_MPEG2_SVCD` | MPEG-2 SVCD-compatible stream

`V4L2_CID_MPEG_STREAM_PID_PMT` | integer |
| Program Map Table Packet ID for the MPEG transport stream (default 16)
`V4L2_CID_MPEG_STREAM_PID_AUDIO` | integer |
| Audio Packet ID for the MPEG transport stream (default 256)
`V4L2_CID_MPEG_STREAM_PID_VIDEO` | integer |
| Video Packet ID for the MPEG transport stream (default 260)
`V4L2_CID_MPEG_STREAM_PID_PCR` | integer |
| Packet ID for the MPEG transport stream carrying PCR fields (default 259)
`V4L2_CID_MPEG_STREAM_PES_ID_AUDIO` | integer |
| Audio ID for MPEG PES
`V4L2_CID_MPEG_STREAM_PES_ID_VIDEO` | integer |
| Video ID for MPEG PES
`V4L2_CID_MPEG_STREAM_VBI_FMT` | enum v4l2_mpeg_stream_vbi_fmt |
| Some cards can embed VBI data (e. g. Closed Caption, Teletext) into the MPEG stream. This control selects whether VBI data should be embedded, and if so, what embedding method should be used. The list of possible VBI formats depends on the driver. The currently defined VBI format types are:

`V4L2_MPEG_STREAM_VBI_FMT_NONE` | No VBI in the MPEG stream
`V4L2_MPEG_STREAM_VBI_FMT_IVTV` | VBI in private packets, IVTV format (documented in the kernel sources in the file `Documentation/video4linux/cx2341x/README.vbi`)

`V4L2_CID_MPEG_AUDIO_SAMPLING_FREQ` | enum v4l2_mpeg_audio_sampling_freq |
| MPEG Audio sampling frequency. Possible values are:

`V4L2_MPEG_AUDIO_SAMPLING_FREQ_44100` | 44.1 kHz
`V4L2_MPEG_AUDIO_SAMPLING_FREQ_48000` | 48 kHz
`V4L2_MPEG_AUDIO_SAMPLING_FREQ_32000` | 32 kHz

`V4L2_CID_MPEG_AUDIO_ENCODING` | enum v4l2_mpeg_audio_encoding |
| MPEG Audio encoding. This control is specific to multiplexed MPEG streams. Possible values are:

`V4L2_MPEG_AUDIO_ENCODING_LAYER_1` | MPEG-1/2 Layer I encoding
`V4L2_MPEG_AUDIO_ENCODING_LAYER_2` | MPEG-1/2 Layer II encoding
`V4L2_MPEG_AUDIO_ENCODING_LAYER_3` | MPEG-1/2 Layer III encoding
`V4L2_MPEG_AUDIO_ENCODING_AAC` | MPEG-2/4 AAC (Advanced Audio Coding)
`V4L2_MPEG_AUDIO_ENCODING_AC3` | AC-3 aka ATSC A/52 encoding

`V4L2_CID_MPEG_AUDIO_L1_BITRATE` | enum v4l2_mpeg_audio_l1_bitrate |
| MPEG-1/2 Layer I bitrate. Possible values are:

`V4L2_MPEG_AUDIO_L1_BITRATE_32K` | 32 kbit/s
`V4L2_MPEG_AUDIO_L1_BITRATE_64K` | 64 kbit/s
`V4L2_MPEG_AUDIO_L1_BITRATE_96K` | 96 kbit/s
`V4L2_MPEG_AUDIO_L1_BITRATE_128K` | 128 kbit/s
`V4L2_MPEG_AUDIO_L1_BITRATE_160K` | 160 kbit/s
`V4L2_MPEG_AUDIO_L1_BITRATE_192K` | 192 kbit/s
`V4L2_MPEG_AUDIO_L1_BITRATE_224K` | 224 kbit/s
`V4L2_MPEG_AUDIO_L1_BITRATE_256K` | 256 kbit/s
`V4L2_MPEG_AUDIO_L1_BITRATE_288K` | 288 kbit/s
`V4L2_MPEG_AUDIO_L1_BITRATE_320K` | 320 kbit/s
`V4L2_MPEG_AUDIO_L1_BITRATE_352K` | 352 kbit/s
`V4L2_MPEG_AUDIO_L1_BITRATE_384K` | 384 kbit/s
`V4L2_MPEG_AUDIO_L1_BITRATE_416K` | 416 kbit/s
`V4L2_MPEG_AUDIO_L1_BITRATE_448K` | 448 kbit/s

`V4L2_CID_MPEG_AUDIO_L2_BITRATE` | enum v4l2_mpeg_audio_l2_bitrate |
| MPEG-1/2 Layer II bitrate. Possible values are:

`V4L2_MPEG_AUDIO_L2_BITRATE_32K` | 32 kbit/s
`V4L2_MPEG_AUDIO_L2_BITRATE_48K` | 48 kbit/s
`V4L2_MPEG_AUDIO_L2_BITRATE_56K` | 56 kbit/s
`V4L2_MPEG_AUDIO_L2_BITRATE_64K` | 64 kbit/s
`V4L2_MPEG_AUDIO_L2_BITRATE_80K` | 80 kbit/s
`V4L2_MPEG_AUDIO_L2_BITRATE_96K` | 96 kbit/s
`V4L2_MPEG_AUDIO_L2_BITRATE_112K` | 112 kbit/s
`V4L2_MPEG_AUDIO_L2_BITRATE_128K` | 128 kbit/s
`V4L2_MPEG_AUDIO_L2_BITRATE_160K` | 160 kbit/s
`V4L2_MPEG_AUDIO_L2_BITRATE_192K` | 192 kbit/s
`V4L2_MPEG_AUDIO_L2_BITRATE_224K` | 224 kbit/s
`V4L2_MPEG_AUDIO_L2_BITRATE_256K` | 256 kbit/s
`V4L2_MPEG_AUDIO_L2_BITRATE_320K` | 320 kbit/s
`V4L2_MPEG_AUDIO_L2_BITRATE_384K` | 384 kbit/s

`V4L2_CID_MPEG_AUDIO_L3_BITRATE` | enum v4l2_mpeg_audio_l3_bitrate |
| MPEG-1/2 Layer III bitrate. Possible values are:

`V4L2_MPEG_AUDIO_L3_BITRATE_32K` | 32 kbit/s
`V4L2_MPEG_AUDIO_L3_BITRATE_40K` | 40 kbit/s
`V4L2_MPEG_AUDIO_L3_BITRATE_48K` | 48 kbit/s
`V4L2_MPEG_AUDIO_L3_BITRATE_56K` | 56 kbit/s
`V4L2_MPEG_AUDIO_L3_BITRATE_64K` | 64 kbit/s
`V4L2_MPEG_AUDIO_L3_BITRATE_80K` | 80 kbit/s
`V4L2_MPEG_AUDIO_L3_BITRATE_96K` | 96 kbit/s
`V4L2_MPEG_AUDIO_L3_BITRATE_112K` | 112 kbit/s
`V4L2_MPEG_AUDIO_L3_BITRATE_128K` | 128 kbit/s
`V4L2_MPEG_AUDIO_L3_BITRATE_160K` | 160 kbit/s
`V4L2_MPEG_AUDIO_L3_BITRATE_192K` | 192 kbit/s
`V4L2_MPEG_AUDIO_L3_BITRATE_224K` | 224 kbit/s
`V4L2_MPEG_AUDIO_L3_BITRATE_256K` | 256 kbit/s
`V4L2_MPEG_AUDIO_L3_BITRATE_320K` | 320 kbit/s

`V4L2_CID_MPEG_AUDIO_AAC_BITRATE` | integer |
| AAC bitrate in bits per second.
`V4L2_CID_MPEG_AUDIO_AC3_BITRATE` | enum v4l2_mpeg_audio_ac3_bitrate |
| AC-3 bitrate. Possible values are:

`V4L2_MPEG_AUDIO_AC3_BITRATE_32K` | 32 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_40K` | 40 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_48K` | 48 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_56K` | 56 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_64K` | 64 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_80K` | 80 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_96K` | 96 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_112K` | 112 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_128K` | 128 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_160K` | 160 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_192K` | 192 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_224K` | 224 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_256K` | 256 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_320K` | 320 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_384K` | 384 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_448K` | 448 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_512K` | 512 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_576K` | 576 kbit/s
`V4L2_MPEG_AUDIO_AC3_BITRATE_640K` | 640 kbit/s

`V4L2_CID_MPEG_AUDIO_MODE` | enum v4l2_mpeg_audio_mode |
| MPEG Audio mode. Possible values are:

`V4L2_MPEG_AUDIO_MODE_STEREO` | Stereo
`V4L2_MPEG_AUDIO_MODE_JOINT_STEREO` | Joint Stereo
`V4L2_MPEG_AUDIO_MODE_DUAL` | Bilingual
`V4L2_MPEG_AUDIO_MODE_MONO` | Mono

`V4L2_CID_MPEG_AUDIO_MODE_EXTENSION` | enum v4l2_mpeg_audio_mode_extension |
| Joint Stereo audio mode extension. In Layer I and II they indicate which subbands are in intensity stereo. All other subbands are coded in stereo. Layer III is not (yet) supported. Possible values are:

`V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_4` | Subbands 4-31 in intensity stereo
`V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_8` | Subbands 8-31 in intensity stereo
`V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_12` | Subbands 12-31 in intensity stereo
`V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_16` | Subbands 16-31 in intensity stereo

`V4L2_CID_MPEG_AUDIO_EMPHASIS` | enum v4l2_mpeg_audio_emphasis |
| Audio Emphasis. Possible values are:

`V4L2_MPEG_AUDIO_EMPHASIS_NONE` | None
`V4L2_MPEG_AUDIO_EMPHASIS_50_DIV_15_uS` | 50/15 microsecond emphasis
`V4L2_MPEG_AUDIO_EMPHASIS_CCITT_J17` | CCITT J.17

`V4L2_CID_MPEG_AUDIO_CRC` | enum v4l2_mpeg_audio_crc |
| CRC method. Possible values are:

`V4L2_MPEG_AUDIO_CRC_NONE` | None
`V4L2_MPEG_AUDIO_CRC_CRC16` | 16 bit parity check

`V4L2_CID_MPEG_AUDIO_MUTE` | boolean |
| Mutes the audio when capturing. This is not done by muting audio hardware, which can still produce a slight hiss, but in the encoder itself, guaranteeing a fixed and reproducible audio bitstream. 0 = unmuted, 1 = muted.
`V4L2_CID_MPEG_AUDIO_DEC_PLAYBACK` | enum v4l2_mpeg_audio_dec_playback |
| Determines how monolingual audio should be played back. Possible values are:

`V4L2_MPEG_AUDIO_DEC_PLAYBACK_AUTO` | Automatically determines the best playback mode.
`V4L2_MPEG_AUDIO_DEC_PLAYBACK_STEREO` | Stereo playback.
`V4L2_MPEG_AUDIO_DEC_PLAYBACK_LEFT` | Left channel playback.
`V4L2_MPEG_AUDIO_DEC_PLAYBACK_RIGHT` | Right channel playback.
`V4L2_MPEG_AUDIO_DEC_PLAYBACK_MONO` | Mono playback.
`V4L2_MPEG_AUDIO_DEC_PLAYBACK_SWAPPED_STEREO` | Stereo playback with swapped left and right channels.

`V4L2_CID_MPEG_AUDIO_DEC_MULTILINGUAL_PLAYBACK` | enum v4l2_mpeg_audio_dec_playback |
| Determines how multilingual audio should be played back.
`V4L2_CID_MPEG_VIDEO_ENCODING` | enum v4l2_mpeg_video_encoding |
| MPEG Video encoding method. This control is specific to multiplexed MPEG streams. Possible values are:

`V4L2_MPEG_VIDEO_ENCODING_MPEG_1` | MPEG-1 Video encoding
`V4L2_MPEG_VIDEO_ENCODING_MPEG_2` | MPEG-2 Video encoding
`V4L2_MPEG_VIDEO_ENCODING_MPEG_4_AVC` | MPEG-4 AVC (H.264) Video encoding

`V4L2_CID_MPEG_VIDEO_ASPECT` | enum v4l2_mpeg_video_aspect |
| Video aspect. Possible values are:

`V4L2_MPEG_VIDEO_ASPECT_1x1` |
`V4L2_MPEG_VIDEO_ASPECT_4x3` |
`V4L2_MPEG_VIDEO_ASPECT_16x9` |
`V4L2_MPEG_VIDEO_ASPECT_221x100` |

`V4L2_CID_MPEG_VIDEO_B_FRAMES` | integer |
| Number of B-Frames (default 2)
`V4L2_CID_MPEG_VIDEO_GOP_SIZE` | integer |
| GOP size (default 12)
`V4L2_CID_MPEG_VIDEO_GOP_CLOSURE` | boolean |
| GOP closure (default 1)
`V4L2_CID_MPEG_VIDEO_PULLDOWN` | boolean |
| Enable 3:2 pulldown (default 0)
`V4L2_CID_MPEG_VIDEO_BITRATE_MODE` | enum v4l2_mpeg_video_bitrate_mode |
| Video bitrate mode. Possible values are:

`V4L2_MPEG_VIDEO_BITRATE_MODE_VBR` | Variable bitrate
`V4L2_MPEG_VIDEO_BITRATE_MODE_CBR` | Constant bitrate

`V4L2_CID_MPEG_VIDEO_BITRATE` | integer |
| Video bitrate in bits per second.
`V4L2_CID_MPEG_VIDEO_BITRATE_PEAK` | integer |
| Peak video bitrate in bits per second. Must be larger or equal to the average video bitrate. It is ignored if the video bitrate mode is set to constant bitrate.
`V4L2_CID_MPEG_VIDEO_TEMPORAL_DECIMATION` | integer |
| For every captured frame, skip this many subsequent frames (default 0).
`V4L2_CID_MPEG_VIDEO_MUTE` | boolean |
| "Mutes" the video to a fixed color when capturing. This is useful for testing, to produce a fixed video bitstream. 0 = unmuted, 1 = muted.
`V4L2_CID_MPEG_VIDEO_MUTE_YUV` | integer |
| Sets the "mute" color of the video. The supplied 32-bit integer is interpreted as follows (bit 0 = least significant bit):

Bit 0:7 | V chrominance information
Bit 8:15 | U chrominance information
Bit 16:23 | Y luminance information
Bit 24:31 | Must be zero.

`V4L2_CID_MPEG_VIDEO_DEC_PTS` | integer64 |
| This read-only control returns the 33-bit video Presentation Time Stamp as defined in ITU T-REC-H.222.0 and ISO/IEC 13818-1 of the currently displayed frame. This is the same PTS as is used in `VIDIOC_DECODER_CMD`.
`V4L2_CID_MPEG_VIDEO_DEC_FRAME` | integer64 |
| This read-only control returns the frame counter of the frame that is currently displayed (decoded). This value is reset to 0 whenever the decoder is started.
`V4L2_CID_MPEG_VIDEO_DECODER_SLICE_INTERFACE` | boolean |
| If enabled the decoder expects to receive a single slice per buffer, otherwise the decoder expects a single frame in per buffer. Applicable to the decoder, all codecs.
`V4L2_CID_MPEG_VIDEO_H264_VUI_SAR_ENABLE` | boolean |
| Enable writing sample aspect ratio in the Video Usability Information. Applicable to the H264 encoder.
`V4L2_CID_MPEG_VIDEO_H264_VUI_SAR_IDC` | enum v4l2_mpeg_video_h264_vui_sar_idc |
| VUI sample aspect ratio indicator for H.264 encoding. The value is defined in the table E-1 in the standard. Applicable to the H264 encoder.

`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_UNSPECIFIED` | Unspecified
`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_1x1` | 1x1
`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_12x11` | 12x11
`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_10x11` | 10x11
`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_16x11` | 16x11
`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_40x33` | 40x33
`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_24x11` | 24x11
`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_20x11` | 20x11
`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_32x11` | 32x11
`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_80x33` | 80x33
`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_18x11` | 18x11
`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_15x11` | 15x11
`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_64x33` | 64x33
`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_160x99` | 160x99
`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_4x3` | 4x3
`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_3x2` | 3x2
`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_2x1` | 2x1
`V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_EXTENDED` | Extended SAR

`V4L2_CID_MPEG_VIDEO_H264_VUI_EXT_SAR_WIDTH` | integer |
| Extended sample aspect ratio width for H.264 VUI encoding. Applicable to the H264 encoder.
`V4L2_CID_MPEG_VIDEO_H264_VUI_EXT_SAR_HEIGHT` | integer |
| Extended sample aspect ratio height for H.264 VUI encoding. Applicable to the H264 encoder.
`V4L2_CID_MPEG_VIDEO_H264_LEVEL` | enum v4l2_mpeg_video_h264_level |
| The level information for the H264 video elementary stream. Applicable to the H264 encoder. Possible values are:

`V4L2_MPEG_VIDEO_H264_LEVEL_1_0` | Level 1.0
`V4L2_MPEG_VIDEO_H264_LEVEL_1B` | Level 1B
`V4L2_MPEG_VIDEO_H264_LEVEL_1_1` | Level 1.1
`V4L2_MPEG_VIDEO_H264_LEVEL_1_2` | Level 1.2
`V4L2_MPEG_VIDEO_H264_LEVEL_1_3` | Level 1.3
`V4L2_MPEG_VIDEO_H264_LEVEL_2_0` | Level 2.0
`V4L2_MPEG_VIDEO_H264_LEVEL_2_1` | Level 2.1
`V4L2_MPEG_VIDEO_H264_LEVEL_2_2` | Level 2.2
`V4L2_MPEG_VIDEO_H264_LEVEL_3_0` | Level 3.0
`V4L2_MPEG_VIDEO_H264_LEVEL_3_1` | Level 3.1
`V4L2_MPEG_VIDEO_H264_LEVEL_3_2` | Level 3.2
`V4L2_MPEG_VIDEO_H264_LEVEL_4_0` | Level 4.0
`V4L2_MPEG_VIDEO_H264_LEVEL_4_1` | Level 4.1
`V4L2_MPEG_VIDEO_H264_LEVEL_4_2` | Level 4.2
`V4L2_MPEG_VIDEO_H264_LEVEL_5_0` | Level 5.0
`V4L2_MPEG_VIDEO_H264_LEVEL_5_1` | Level 5.1

`V4L2_CID_MPEG_VIDEO_MPEG4_LEVEL` | enum v4l2_mpeg_video_mpeg4_level |
| The level information for the MPEG4 elementary stream. Applicable to the MPEG4 encoder. Possible values are:

`V4L2_MPEG_VIDEO_LEVEL_0` | Level 0
`V4L2_MPEG_VIDEO_LEVEL_0B` | Level 0b
`V4L2_MPEG_VIDEO_LEVEL_1` | Level 1
`V4L2_MPEG_VIDEO_LEVEL_2` | Level 2
`V4L2_MPEG_VIDEO_LEVEL_3` | Level 3
`V4L2_MPEG_VIDEO_LEVEL_3B` | Level 3b
`V4L2_MPEG_VIDEO_LEVEL_4` | Level 4
`V4L2_MPEG_VIDEO_LEVEL_5` | Level 5

`V4L2_CID_MPEG_VIDEO_H264_PROFILE` | enum v4l2_mpeg_video_h264_profile |
| The profile information for H264. Applicable to the H264 encoder. Possible values are:

`V4L2_MPEG_VIDEO_H264_PROFILE_BASELINE` | Baseline profile
`V4L2_MPEG_VIDEO_H264_PROFILE_CONSTRAINED_BASELINE` | Constrained Baseline profile
`V4L2_MPEG_VIDEO_H264_PROFILE_MAIN` | Main profile
`V4L2_MPEG_VIDEO_H264_PROFILE_EXTENDED` | Extended profile
`V4L2_MPEG_VIDEO_H264_PROFILE_HIGH` | High profile
`V4L2_MPEG_VIDEO_H264_PROFILE_HIGH_10` | High 10 profile
`V4L2_MPEG_VIDEO_H264_PROFILE_HIGH_422` | High 422 profile
`V4L2_MPEG_VIDEO_H264_PROFILE_HIGH_444_PREDICTIVE` | High 444 Predictive profile
`V4L2_MPEG_VIDEO_H264_PROFILE_HIGH_10_INTRA` | High 10 Intra profile
`V4L2_MPEG_VIDEO_H264_PROFILE_HIGH_422_INTRA` | High 422 Intra profile
`V4L2_MPEG_VIDEO_H264_PROFILE_HIGH_444_INTRA` | High 444 Intra profile
`V4L2_MPEG_VIDEO_H264_PROFILE_CAVLC_444_INTRA` | CAVLC 444 Intra profile
`V4L2_MPEG_VIDEO_H264_PROFILE_SCALABLE_BASELINE` | Scalable Baseline profile
`V4L2_MPEG_VIDEO_H264_PROFILE_SCALABLE_HIGH` | Scalable High profile
`V4L2_MPEG_VIDEO_H264_PROFILE_SCALABLE_HIGH_INTRA` | Scalable High Intra profile
`V4L2_MPEG_VIDEO_H264_PROFILE_STEREO_HIGH` | Stereo High profile
`V4L2_MPEG_VIDEO_H264_PROFILE_MULTIVIEW_HIGH` | Multiview High profile

`V4L2_CID_MPEG_VIDEO_MPEG4_PROFILE` | enum v4l2_mpeg_video_mpeg4_profile |
| The profile information for MPEG4. Applicable to the MPEG4 encoder. Possible values are:

`V4L2_MPEG_VIDEO_PROFILE_SIMPLE` | Simple profile
`V4L2_MPEG_VIDEO_PROFILE_ADVANCED_SIMPLE` | Advanced Simple profile
`V4L2_MPEG_VIDEO_PROFILE_CORE` | Core profile
`V4L2_MPEG_VIDEO_PROFILE_SIMPLE_SCALABLE` | Simple Scalable profile
`V4L2_MPEG_VIDEO_PROFILE_ADVANCED_CODING_EFFICIENCY` |

`V4L2_CID_MPEG_VIDEO_MAX_REF_PIC` | integer |
| The maximum number of reference pictures used for encoding. Applicable to the encoder.
`V4L2_CID_MPEG_VIDEO_MULTI_SLICE_MODE` | enum v4l2_mpeg_video_multi_slice_mode |
| Determines how the encoder should handle division of frame into slices. Applicable to the encoder. Possible values are:

`V4L2_MPEG_VIDEO_MULTI_SLICE_MODE_SINGLE` | Single slice per frame.
`V4L2_MPEG_VIDEO_MULTI_SLICE_MODE_MAX_MB` | Multiple slices with set maximum number of macroblocks per slice.
`V4L2_MPEG_VIDEO_MULTI_SLICE_MODE_MAX_BYTES` | Multiple slice with set maximum size in bytes per slice.

`V4L2_CID_MPEG_VIDEO_MULTI_SLICE_MAX_MB` | integer |
| The maximum number of macroblocks in a slice. Used when `V4L2_CID_MPEG_VIDEO_MULTI_SLICE_MODE` is set to `V4L2_MPEG_VIDEO_MULTI_SLICE_MODE_MAX_MB`. Applicable to the encoder.
`V4L2_CID_MPEG_VIDEO_MULTI_SLICE_MAX_BYTES` | integer |
| The maximum size of a slice in bytes. Used when `V4L2_CID_MPEG_VIDEO_MULTI_SLICE_MODE` is set to `V4L2_MPEG_VIDEO_MULTI_SLICE_MODE_MAX_BYTES`. Applicable to the encoder.
`V4L2_CID_MPEG_VIDEO_H264_LOOP_FILTER_MODE` | enum v4l2_mpeg_video_h264_loop_filter_mode |
| Loop filter mode for H264 encoder. Possible values are:

`V4L2_MPEG_VIDEO_H264_LOOP_FILTER_MODE_ENABLED` | Loop filter is enabled.
`V4L2_MPEG_VIDEO_H264_LOOP_FILTER_MODE_DISABLED` | Loop filter is disabled.
`V4L2_MPEG_VIDEO_H264_LOOP_FILTER_MODE_DISABLED_AT_SLICE_BOUNDARY` | Loop filter is disabled at the slice boundary.

`V4L2_CID_MPEG_VIDEO_H264_LOOP_FILTER_ALPHA` | integer |
| Loop filter alpha coefficient, defined in the H264 standard. Applicable to the H264 encoder.
`V4L2_CID_MPEG_VIDEO_H264_LOOP_FILTER_BETA` | integer |
| Loop filter beta coefficient, defined in the H264 standard. Applicable to the H264 encoder.
`V4L2_CID_MPEG_VIDEO_H264_ENTROPY_MODE` | enum v4l2_mpeg_video_h264_entropy_mode |
| Entropy coding mode for H264 - CABAC/CAVALC. Applicable to the H264 encoder. Possible values are:

`V4L2_MPEG_VIDEO_H264_ENTROPY_MODE_CAVLC` | Use CAVLC entropy coding.
`V4L2_MPEG_VIDEO_H264_ENTROPY_MODE_CABAC` | Use CABAC entropy coding.

`V4L2_CID_MPEG_VIDEO_H264_8X8_TRANSFORM` | boolean |
| Enable 8X8 transform for H264. Applicable to the H264 encoder.
`V4L2_CID_MPEG_VIDEO_CYCLIC_INTRA_REFRESH_MB` | integer |
| Cyclic intra macroblock refresh. This is the number of continuous macroblocks refreshed every frame. Each frame a successive set of macroblocks is refreshed until the cycle completes and starts from the top of the frame. Applicable to H264, H263 and MPEG4 encoder.
`V4L2_CID_MPEG_VIDEO_FRAME_RC_ENABLE` | boolean |

Frame level rate control enable. If this control is disabled then the quantization parameter for each frame type is constant and set with appropriate controls (e.g. `V4L2_CID_MPEG_VIDEO_H263_I_FRAME_QP`). If frame rate control is enabled then quantization parameter is adjusted to meet the chosen bitrate. Minimum and maximum value for the quantization parameter can be set with appropriate controls (e.g. `V4L2_CID_MPEG_VIDEO_H263_MIN_QP`). Applicable to encoders.

`V4L2_CID_MPEG_VIDEO_MB_RC_ENABLE` | boolean |
| Macroblock level rate control enable. Applicable to the MPEG4 and H264 encoders.
`V4L2_CID_MPEG_VIDEO_MPEG4_QPEL` | boolean |
| Quarter pixel motion estimation for MPEG4. Applicable to the MPEG4 encoder.
`V4L2_CID_MPEG_VIDEO_H263_I_FRAME_QP` | integer |
| Quantization parameter for an I frame for H263. Valid range: from 1 to 31.
`V4L2_CID_MPEG_VIDEO_H263_MIN_QP` | integer |
| Minimum quantization parameter for H263. Valid range: from 1 to 31.
`V4L2_CID_MPEG_VIDEO_H263_MAX_QP` | integer |
| Maximum quantization parameter for H263. Valid range: from 1 to 31.
`V4L2_CID_MPEG_VIDEO_H263_P_FRAME_QP` | integer |
| Quantization parameter for an P frame for H263. Valid range: from 1 to 31.
`V4L2_CID_MPEG_VIDEO_H263_B_FRAME_QP` | integer |
| Quantization parameter for an B frame for H263. Valid range: from 1 to 31.
`V4L2_CID_MPEG_VIDEO_H264_I_FRAME_QP` | integer |
| Quantization parameter for an I frame for H264. Valid range: from 0 to 51.
`V4L2_CID_MPEG_VIDEO_H264_MIN_QP` | integer |
| Minimum quantization parameter for H264. Valid range: from 0 to 51.
`V4L2_CID_MPEG_VIDEO_H264_MAX_QP` | integer |
| Maximum quantization parameter for H264. Valid range: from 0 to 51.
`V4L2_CID_MPEG_VIDEO_H264_P_FRAME_QP` | integer |
| Quantization parameter for an P frame for H264. Valid range: from 0 to 51.
`V4L2_CID_MPEG_VIDEO_H264_B_FRAME_QP` | integer |
| Quantization parameter for an B frame for H264. Valid range: from 0 to 51.
`V4L2_CID_MPEG_VIDEO_MPEG4_I_FRAME_QP` | integer |
| Quantization parameter for an I frame for MPEG4. Valid range: from 1 to 31.
`V4L2_CID_MPEG_VIDEO_MPEG4_MIN_QP` | integer |
| Minimum quantization parameter for MPEG4. Valid range: from 1 to 31.
`V4L2_CID_MPEG_VIDEO_MPEG4_MAX_QP` | integer |
| Maximum quantization parameter for MPEG4. Valid range: from 1 to 31.
`V4L2_CID_MPEG_VIDEO_MPEG4_P_FRAME_QP` | integer |
| Quantization parameter for an P frame for MPEG4. Valid range: from 1 to 31.
`V4L2_CID_MPEG_VIDEO_MPEG4_B_FRAME_QP` | integer |
| Quantization parameter for an B frame for MPEG4. Valid range: from 1 to 31.
`V4L2_CID_MPEG_VIDEO_VBV_SIZE` | integer |

The Video Buffer Verifier size in kilobytes, it is used as a limitation of frame skip. The VBV is defined in the standard as a mean to verify that the produced stream will be successfully decoded. The standard describes it as "Part of a hypothetical decoder that is conceptually connected to the output of the encoder. Its purpose is to provide a constraint on the variability of the data rate that an encoder or editing process may produce.". Applicable to the MPEG1, MPEG2, MPEG4 encoders.

`V4L2_CID_MPEG_VIDEO_VBV_DELAY` | integer |
| Sets the initial delay in milliseconds for VBV buffer control.
`V4L2_CID_MPEG_VIDEO_H264_CPB_SIZE` | integer |
| The Coded Picture Buffer size in kilobytes, it is used as a limitation of frame skip. The CPB is defined in the H264 standard as a mean to verify that the produced stream will be successfully decoded. Applicable to the H264 encoder.
`V4L2_CID_MPEG_VIDEO_H264_I_PERIOD` | integer |

Period between I-frames in the open GOP for H264. In case of an open GOP this is the period between two I-frames. The period between IDR (Instantaneous Decoding Refresh) frames is taken from the GOP_SIZE control. An IDR frame, which stands for Instantaneous Decoding Refresh is an I-frame after which no prior frames are referenced. This means that a stream can be restarted from an IDR frame without the need to store or decode any previous frames. Applicable to the H264 encoder.

`V4L2_CID_MPEG_VIDEO_HEADER_MODE` | enum v4l2_mpeg_video_header_mode |
| Determines whether the header is returned as the first buffer or is it returned together with the first frame. Applicable to encoders. Possible values are:

`V4L2_MPEG_VIDEO_HEADER_MODE_SEPARATE` | The stream header is returned separately in the first buffer.
`V4L2_MPEG_VIDEO_HEADER_MODE_JOINED_WITH_1ST_FRAME` | The stream header is returned together with the first encoded frame.

`V4L2_CID_MPEG_VIDEO_REPEAT_SEQ_HEADER` | boolean |
| Repeat the video sequence headers. Repeating these headers makes random access to the video stream easier. Applicable to the MPEG1, 2 and 4 encoder.
`V4L2_CID_MPEG_VIDEO_DECODER_MPEG4_DEBLOCK_FILTER` | boolean |
| Enabled the deblocking post processing filter for MPEG4 decoder. Applicable to the MPEG4 decoder.
`V4L2_CID_MPEG_VIDEO_MPEG4_VOP_TIME_RES` | integer |
| vop_time_increment_resolution value for MPEG4. Applicable to the MPEG4 encoder.
`V4L2_CID_MPEG_VIDEO_MPEG4_VOP_TIME_INC` | integer |
| vop_time_increment value for MPEG4. Applicable to the MPEG4 encoder.
`V4L2_CID_MPEG_VIDEO_H264_SEI_FRAME_PACKING` | boolean |
| Enable generation of frame packing supplemental enhancement information in the encoded bitstream. The frame packing SEI message contains the arrangement of L and R planes for 3D viewing. Applicable to the H264 encoder.
`V4L2_CID_MPEG_VIDEO_H264_SEI_FP_CURRENT_FRAME_0` | boolean |
| Sets current frame as frame0 in frame packing SEI. Applicable to the H264 encoder.
`V4L2_CID_MPEG_VIDEO_H264_SEI_FP_ARRANGEMENT_TYPE` | enum v4l2_mpeg_video_h264_sei_fp_arrangement_type |
| Frame packing arrangement type for H264 SEI. Applicable to the H264 encoder. Possible values are:

`V4L2_MPEG_VIDEO_H264_SEI_FP_ARRANGEMENT_TYPE_CHEKERBOARD` | Pixels are alternatively from L and R.
`V4L2_MPEG_VIDEO_H264_SEI_FP_ARRANGEMENT_TYPE_COLUMN` | L and R are interlaced by column.
`V4L2_MPEG_VIDEO_H264_SEI_FP_ARRANGEMENT_TYPE_ROW` | L and R are interlaced by row.
`V4L2_MPEG_VIDEO_H264_SEI_FP_ARRANGEMENT_TYPE_SIDE_BY_SIDE` | L is on the left, R on the right.
`V4L2_MPEG_VIDEO_H264_SEI_FP_ARRANGEMENT_TYPE_TOP_BOTTOM` | L is on top, R on bottom.
`V4L2_MPEG_VIDEO_H264_SEI_FP_ARRANGEMENT_TYPE_TEMPORAL` | One view per frame.

`V4L2_CID_MPEG_VIDEO_H264_FMO` | boolean |
| Enables flexible macroblock ordering in the encoded bitstream. It is a technique used for restructuring the ordering of macroblocks in pictures. Applicable to the H264 encoder.
`V4L2_CID_MPEG_VIDEO_H264_FMO_MAP_TYPE` | enum v4l2_mpeg_video_h264_fmo_map_type |
| When using FMO, the map type divides the image in different scan patterns of macroblocks. Applicable to the H264 encoder. Possible values are:

`V4L2_MPEG_VIDEO_H264_FMO_MAP_TYPE_INTERLEAVED_SLICES` | Slices are interleaved one after other with macroblocks in run length order.
`V4L2_MPEG_VIDEO_H264_FMO_MAP_TYPE_SCATTERED_SLICES` | Scatters the macroblocks based on a mathematical function known to both encoder and decoder.
`V4L2_MPEG_VIDEO_H264_FMO_MAP_TYPE_FOREGROUND_WITH_LEFT_OVER` | Macroblocks arranged in rectangular areas or regions of interest.
`V4L2_MPEG_VIDEO_H264_FMO_MAP_TYPE_BOX_OUT` | Slice groups grow in a cyclic way from centre to outwards.
`V4L2_MPEG_VIDEO_H264_FMO_MAP_TYPE_RASTER_SCAN` | Slice groups grow in raster scan pattern from left to right.
`V4L2_MPEG_VIDEO_H264_FMO_MAP_TYPE_WIPE_SCAN` | Slice groups grow in wipe scan pattern from top to bottom.
`V4L2_MPEG_VIDEO_H264_FMO_MAP_TYPE_EXPLICIT` | User defined map type.

`V4L2_CID_MPEG_VIDEO_H264_FMO_SLICE_GROUP` | integer |
| Number of slice groups in FMO. Applicable to the H264 encoder.
`V4L2_CID_MPEG_VIDEO_H264_FMO_CHANGE_DIRECTION` | enum v4l2_mpeg_video_h264_fmo_change_dir |
| Specifies a direction of the slice group change for raster and wipe maps. Applicable to the H264 encoder. Possible values are:

`V4L2_MPEG_VIDEO_H264_FMO_CHANGE_DIR_RIGHT` | Raster scan or wipe right.
`V4L2_MPEG_VIDEO_H264_FMO_CHANGE_DIR_LEFT` | Reverse raster scan or wipe left.

`V4L2_CID_MPEG_VIDEO_H264_FMO_CHANGE_RATE` | integer |
| Specifies the size of the first slice group for raster and wipe map. Applicable to the H264 encoder.
`V4L2_CID_MPEG_VIDEO_H264_FMO_RUN_LENGTH` | integer |
| Specifies the number of consecutive macroblocks for the interleaved map. Applicable to the H264 encoder.
`V4L2_CID_MPEG_VIDEO_H264_ASO` | boolean |
| Enables arbitrary slice ordering in encoded bitstream. Applicable to the H264 encoder.
`V4L2_CID_MPEG_VIDEO_H264_ASO_SLICE_ORDER` | integer |
| Specifies the slice order in ASO. Applicable to the H264 encoder. The supplied 32-bit integer is interpreted as follows (bit 0 = least significant bit):

Bit 0:15 | Slice ID
Bit 16:32 | Slice position or order

`V4L2_CID_MPEG_VIDEO_H264_HIERARCHICAL_CODING` | boolean |
| Enables H264 hierarchical coding. Applicable to the H264 encoder.
`V4L2_CID_MPEG_VIDEO_H264_HIERARCHICAL_CODING_TYPE` | enum v4l2_mpeg_video_h264_hierarchical_coding_type |
| Specifies the hierarchical coding type. Applicable to the H264 encoder. Possible values are:

`V4L2_MPEG_VIDEO_H264_HIERARCHICAL_CODING_B` | Hierarchical B coding.
`V4L2_MPEG_VIDEO_H264_HIERARCHICAL_CODING_P` | Hierarchical P coding.

`V4L2_CID_MPEG_VIDEO_H264_HIERARCHICAL_CODING_LAYER` | integer |
| Specifies the number of hierarchical coding layers. Applicable to the H264 encoder.
`V4L2_CID_MPEG_VIDEO_H264_HIERARCHICAL_CODING_LAYER_QP` | integer |
| Specifies a user defined QP for each layer. Applicable to the H264 encoder. The supplied 32-bit integer is interpreted as follows (bit 0 = least significant bit):

Bit 0:15 | QP value
Bit 16:32 | Layer number

#### MFC 5.1 MPEG Controls

The following MPEG class controls deal with MPEG decoding and encoding settings that are specific to the Multi Format Codec 5.1 device present in the S5P family of SoCs by Samsung.

Table 1.3. MFC 5.1 Control IDs

ID | Type |
| Description
`V4L2_CID_MPEG_MFC51_VIDEO_DECODER_H264_DISPLAY_DELAY_ENABLE` | integer |

If the display delay is enabled then the decoder has to return a CAPTURE buffer after processing a certain number of OUTPUT buffers. If this number is low, then it may result in buffers not being dequeued in display order. In addition hardware may still use those buffers as reference, thus application should not write to those buffers. This feature can be used for example for generating thumbnails of videos. Applicable to the H264 decoder.

`V4L2_CID_MPEG_MFC51_VIDEO_DECODER_H264_DISPLAY_DELAY` | integer |
| Display delay value for H264 decoder. The decoder is forced to return a decoded frame after the set 'display delay' number of frames. If this number is low it may result in frames returned out of dispaly order, in addition the hardware may still be using the returned buffer as a reference picture for subsequent frames.
`V4L2_CID_MPEG_MFC51_VIDEO_H264_NUM_REF_PIC_FOR_P` | integer |
| The number of reference pictures used for encoding a P picture. Applicable to the H264 encoder.
`V4L2_CID_MPEG_MFC51_VIDEO_PADDING` | boolean |
| Padding enable in the encoder - use a color instead of repeating border pixels. Applicable to encoders.
`V4L2_CID_MPEG_MFC51_VIDEO_PADDING_YUV` | integer |
| Padding color in the encoder. Applicable to encoders. The supplied 32-bit integer is interpreted as follows (bit 0 = least significant bit):

Bit 0:7 | V chrominance information
Bit 8:15 | U chrominance information
Bit 16:23 | Y luminance information
Bit 24:31 | Must be zero.

`V4L2_CID_MPEG_MFC51_VIDEO_RC_REACTION_COEFF` | integer |
| Reaction coefficient for MFC rate control. Applicable to encoders. Note 1: Valid only when the frame level RC is enabled. Note 2: For tight CBR, this field must be small (ex. 2 ~ 10). For VBR, this field must be large (ex. 100 ~ 1000). Note 3: It is not recommended to use the greater number than FRAME_RATE * (10^9 / BIT_RATE).
`V4L2_CID_MPEG_MFC51_VIDEO_H264_ADAPTIVE_RC_DARK` | boolean |
| Adaptive rate control for dark region. Valid only when H.264 and macroblock level RC is enabled (`V4L2_CID_MPEG_VIDEO_MB_RC_ENABLE`). Applicable to the H264 encoder.
`V4L2_CID_MPEG_MFC51_VIDEO_H264_ADAPTIVE_RC_SMOOTH` | boolean |
| Adaptive rate control for smooth region. Valid only when H.264 and macroblock level RC is enabled (`V4L2_CID_MPEG_VIDEO_MB_RC_ENABLE`). Applicable to the H264 encoder.
`V4L2_CID_MPEG_MFC51_VIDEO_H264_ADAPTIVE_RC_STATIC` | boolean |
| Adaptive rate control for static region. Valid only when H.264 and macroblock level RC is enabled (`V4L2_CID_MPEG_VIDEO_MB_RC_ENABLE`). Applicable to the H264 encoder.
`V4L2_CID_MPEG_MFC51_VIDEO_H264_ADAPTIVE_RC_ACTIVITY` | boolean |
| Adaptive rate control for activity region. Valid only when H.264 and macroblock level RC is enabled (`V4L2_CID_MPEG_VIDEO_MB_RC_ENABLE`). Applicable to the H264 encoder.
`V4L2_CID_MPEG_MFC51_VIDEO_FRAME_SKIP_MODE` | enum v4l2_mpeg_mfc51_video_frame_skip_mode |
| Indicates in what conditions the encoder should skip frames. If encoding a frame would cause the encoded stream to be larger then a chosen data limit then the frame will be skipped. Possible values are:

`V4L2_MPEG_MFC51_FRAME_SKIP_MODE_DISABLED` | Frame skip mode is disabled.
`V4L2_MPEG_MFC51_FRAME_SKIP_MODE_LEVEL_LIMIT` | Frame skip mode enabled and buffer limit is set by the chosen level and is defined by the standard.
`V4L2_MPEG_MFC51_FRAME_SKIP_MODE_BUF_LIMIT` | Frame skip mode enabled and buffer limit is set by the VBV (MPEG1/2/4) or CPB (H264) buffer size control.

`V4L2_CID_MPEG_MFC51_VIDEO_RC_FIXED_TARGET_BIT` | integer |

Enable rate-control with fixed target bit. If this setting is enabled, then the rate control logic of the encoder will calculate the average bitrate for a GOP and keep it below or equal the set bitrate target. Otherwise the rate control logic calculates the overall average bitrate for the stream and keeps it below or equal to the set bitrate. In the first case the average bitrate for the whole stream will be smaller then the set bitrate. This is caused because the average is calculated for smaller number of frames, on the other hand enabling this setting will ensure that the stream will meet tight bandwidth contraints. Applicable to encoders.

`V4L2_CID_MPEG_MFC51_VIDEO_FORCE_FRAME_TYPE` | enum v4l2_mpeg_mfc51_video_force_frame_type |
| Force a frame type for the next queued buffer. Applicable to encoders. Possible values are:

`V4L2_MPEG_MFC51_FORCE_FRAME_TYPE_DISABLED` | Forcing a specific frame type disabled.
`V4L2_MPEG_MFC51_FORCE_FRAME_TYPE_I_FRAME` | Force an I-frame.
`V4L2_MPEG_MFC51_FORCE_FRAME_TYPE_NOT_CODED` | Force a non-coded frame.

#### CX2341x MPEG Controls

The following MPEG class controls deal with MPEG encoding settings that are specific to the Conexant CX23415 and CX23416 MPEG encoding chips.

Table 1.4. CX2341x Control IDs

ID | Type |
| Description
`V4L2_CID_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE` | enum v4l2_mpeg_cx2341x_video_spatial_filter_mode |
| Sets the Spatial Filter mode (default `MANUAL`). Possible values are:

`V4L2_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE_MANUAL` | Choose the filter manually
`V4L2_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE_AUTO` | Choose the filter automatically

`V4L2_CID_MPEG_CX2341X_VIDEO_SPATIAL_FILTER` | integer (0-15) |
| The setting for the Spatial Filter. 0 = off, 15 = maximum. (Default is 0.)
`V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE` | enum v4l2_mpeg_cx2341x_video_luma_spatial_filter_type |
| Select the algorithm to use for the Luma Spatial Filter (default `1D_HOR`). Possible values:

`V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_OFF` | No filter
`V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_1D_HOR` | One-dimensional horizontal
`V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_1D_VERT` | One-dimensional vertical
`V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_2D_HV_SEPARABLE` | Two-dimensional separable
`V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_2D_SYM_NON_SEPARABLE` | Two-dimensional symmetrical non-separable

`V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_SPATIAL_FILTER_TYPE` | enum v4l2_mpeg_cx2341x_video_chroma_spatial_filter_type |
| Select the algorithm for the Chroma Spatial Filter (default `1D_HOR`). Possible values are:

`V4L2_MPEG_CX2341X_VIDEO_CHROMA_SPATIAL_FILTER_TYPE_OFF` | No filter
`V4L2_MPEG_CX2341X_VIDEO_CHROMA_SPATIAL_FILTER_TYPE_1D_HOR` | One-dimensional horizontal

`V4L2_CID_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER_MODE` | enum v4l2_mpeg_cx2341x_video_temporal_filter_mode |
| Sets the Temporal Filter mode (default `MANUAL`). Possible values are:

`V4L2_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER_MODE_MANUAL` | Choose the filter manually
`V4L2_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER_MODE_AUTO` | Choose the filter automatically

`V4L2_CID_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER` | integer (0-31) |
| The setting for the Temporal Filter. 0 = off, 31 = maximum. (Default is 8 for full-scale capturing and 0 for scaled capturing.)
`V4L2_CID_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE` | enum v4l2_mpeg_cx2341x_video_median_filter_type |
| Median Filter Type (default `OFF`). Possible values are:

`V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_OFF` | No filter
`V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_HOR` | Horizontal filter
`V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_VERT` | Vertical filter
`V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_HOR_VERT` | Horizontal and vertical filter
`V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_DIAG` | Diagonal filter

`V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_MEDIAN_FILTER_BOTTOM` | integer (0-255) |
| Threshold above which the luminance median filter is enabled (default 0)
`V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_MEDIAN_FILTER_TOP` | integer (0-255) |
| Threshold below which the luminance median filter is enabled (default 255)
`V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_MEDIAN_FILTER_BOTTOM` | integer (0-255) |
| Threshold above which the chroma median filter is enabled (default 0)
`V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_MEDIAN_FILTER_TOP` | integer (0-255) |
| Threshold below which the chroma median filter is enabled (default 255)
`V4L2_CID_MPEG_CX2341X_STREAM_INSERT_NAV_PACKETS` | boolean |
| The CX2341X MPEG encoder can insert one empty MPEG-2 PES packet into the stream between every four video frames. The packet size is 2048 bytes, including the packet_start_code_prefix and stream_id fields. The stream_id is 0xBF (private stream 2). The payload consists of 0x00 bytes, to be filled in by the application. 0 = do not insert, 1 = insert packets.

#### VPX Control Reference

The VPX controls include controls for encoding parameters of VPx video codec.

Table 1.5. VPX Control IDs

ID | Type |
| Description
`V4L2_CID_MPEG_VIDEO_VPX_NUM_PARTITIONS` | enum v4l2_vp8_num_partitions |
| The number of token partitions to use in VP8 encoder. Possible values are:

`V4L2_CID_MPEG_VIDEO_VPX_1_PARTITION` | 1 coefficient partition
`V4L2_CID_MPEG_VIDEO_VPX_2_PARTITIONS` | 2 coefficient partitions
`V4L2_CID_MPEG_VIDEO_VPX_4_PARTITIONS` | 4 coefficient partitions
`V4L2_CID_MPEG_VIDEO_VPX_8_PARTITIONS` | 8 coefficient partitions

`V4L2_CID_MPEG_VIDEO_VPX_IMD_DISABLE_4X4` | boolean |
| Setting this prevents intra 4x4 mode in the intra mode decision.
`V4L2_CID_MPEG_VIDEO_VPX_NUM_REF_FRAMES` | enum v4l2_vp8_num_ref_frames |
| The number of reference pictures for encoding P frames. Possible values are:

`V4L2_CID_MPEG_VIDEO_VPX_1_REF_FRAME` | Last encoded frame will be searched
`V4L2_CID_MPEG_VIDEO_VPX_2_REF_FRAME` | Two frames will be searched among the last encoded frame, the golden frame and the alternate reference (altref) frame. The encoder implementation will decide which two are chosen.
`V4L2_CID_MPEG_VIDEO_VPX_3_REF_FRAME` | The last encoded frame, the golden frame and the altref frame will be searched.

`V4L2_CID_MPEG_VIDEO_VPX_FILTER_LEVEL` | integer |
| Indicates the loop filter level. The adjustment of the loop filter level is done via a delta value against a baseline loop filter value.
`V4L2_CID_MPEG_VIDEO_VPX_FILTER_SHARPNESS` | integer |
| This parameter affects the loop filter. Anything above zero weakens the deblocking effect on the loop filter.
`V4L2_CID_MPEG_VIDEO_VPX_GOLDEN_FRAME_REF_PERIOD` | integer |
| Sets the refresh period for the golden frame. The period is defined in number of frames. For a value of 'n', every nth frame starting from the first key frame will be taken as a golden frame. For eg. for encoding sequence of 0, 1, 2, 3, 4, 5, 6, 7 where the golden frame refresh period is set as 4, the frames 0, 4, 8 etc will be taken as the golden frames as frame 0 is always a key frame.
`V4L2_CID_MPEG_VIDEO_VPX_GOLDEN_FRAME_SEL` | enum v4l2_vp8_golden_frame_sel |
| Selects the golden frame for encoding. Possible values are:

`V4L2_CID_MPEG_VIDEO_VPX_GOLDEN_FRAME_USE_PREV` | Use the (n-2)th frame as a golden frame, current frame index being 'n'.
`V4L2_CID_MPEG_VIDEO_VPX_GOLDEN_FRAME_USE_REF_PERIOD` | Use the previous specific frame indicated by V4L2_CID_MPEG_VIDEO_VPX_GOLDEN_FRAME_REF_PERIOD as a golden frame.

### Camera Control Reference

The Camera class includes controls for mechanical (or equivalent digital) features of a device such as controllable lenses or sensors.

Table 1.6. Camera Control IDs

ID | Type |
| Description
`V4L2_CID_CAMERA_CLASS` | class |
| The Camera class descriptor. Calling `VIDIOC_QUERYCTRL` for this control will return a description of this control class.
`V4L2_CID_EXPOSURE_AUTO` | enum v4l2_exposure_auto_type |
| Enables automatic adjustments of the exposure time and/or iris aperture. The effect of manual changes of the exposure time or iris aperture while these features are enabled is undefined, drivers should ignore such requests. Possible values are:

`V4L2_EXPOSURE_AUTO` | Automatic exposure time, automatic iris aperture.
`V4L2_EXPOSURE_MANUAL` | Manual exposure time, manual iris.
`V4L2_EXPOSURE_SHUTTER_PRIORITY` | Manual exposure time, auto iris.
`V4L2_EXPOSURE_APERTURE_PRIORITY` | Auto exposure time, manual iris.

`V4L2_CID_EXPOSURE_ABSOLUTE` | integer |
| Determines the exposure time of the camera sensor. The exposure time is limited by the frame interval. Drivers should interpret the values as 100 µs units, where the value 1 stands for 1/10000th of a second, 10000 for 1 second and 100000 for 10 seconds.
`V4L2_CID_EXPOSURE_AUTO_PRIORITY` | boolean |
| When `V4L2_CID_EXPOSURE_AUTO` is set to `AUTO` or `APERTURE_PRIORITY`, this control determines if the device may dynamically vary the frame rate. By default this feature is disabled (0) and the frame rate must remain constant.
`V4L2_CID_EXPOSURE_BIAS` | integer menu |

Determines the automatic exposure compensation, it is effective only when `V4L2_CID_EXPOSURE_AUTO` control is set to `AUTO`, `SHUTTER_PRIORITY` or `APERTURE_PRIORITY`. It is expressed in terms of EV, drivers should interpret the values as 0.001 EV units, where the value 1000 stands for +1 EV.

Increasing the exposure compensation value is equivalent to decreasing the exposure value (EV) and will increase the amount of light at the image sensor. The camera performs the exposure compensation by adjusting absolute exposure time and/or aperture.

`V4L2_CID_EXPOSURE_METERING` | enum v4l2_exposure_metering |
| Determines how the camera measures the amount of light available for the frame exposure. Possible values are:

`V4L2_EXPOSURE_METERING_AVERAGE` | Use the light information coming from the entire frame and average giving no weighting to any particular portion of the metered area.
`V4L2_EXPOSURE_METERING_CENTER_WEIGHTED` | Average the light information coming from the entire frame giving priority to the center of the metered area.
`V4L2_EXPOSURE_METERING_SPOT` | Measure only very small area at the center of the frame.
`V4L2_EXPOSURE_METERING_MATRIX` | A multi-zone metering. The light intensity is measured in several points of the frame and the the results are combined. The algorithm of the zones selection and their significance in calculating the final value is device dependent.

`V4L2_CID_PAN_RELATIVE` | integer |
| This control turns the camera horizontally by the specified amount. The unit is undefined. A positive value moves the camera to the right (clockwise when viewed from above), a negative value to the left. A value of zero does not cause motion. This is a write-only control.
`V4L2_CID_TILT_RELATIVE` | integer |
| This control turns the camera vertically by the specified amount. The unit is undefined. A positive value moves the camera up, a negative value down. A value of zero does not cause motion. This is a write-only control.
`V4L2_CID_PAN_RESET` | button |
| When this control is set, the camera moves horizontally to the default position.
`V4L2_CID_TILT_RESET` | button |
| When this control is set, the camera moves vertically to the default position.
`V4L2_CID_PAN_ABSOLUTE` | integer |
| This control turns the camera horizontally to the specified position. Positive values move the camera to the right (clockwise when viewed from above), negative values to the left. Drivers should interpret the values as arc seconds, with valid values between -180 * 3600 and +180 * 3600 inclusive.
`V4L2_CID_TILT_ABSOLUTE` | integer |
| This control turns the camera vertically to the specified position. Positive values move the camera up, negative values down. Drivers should interpret the values as arc seconds, with valid values between -180 * 3600 and +180 * 3600 inclusive.
`V4L2_CID_FOCUS_ABSOLUTE` | integer |
| This control sets the focal point of the camera to the specified position. The unit is undefined. Positive values set the focus closer to the camera, negative values towards infinity.
`V4L2_CID_FOCUS_RELATIVE` | integer |
| This control moves the focal point of the camera by the specified amount. The unit is undefined. Positive values move the focus closer to the camera, negative values towards infinity. This is a write-only control.
`V4L2_CID_FOCUS_AUTO` | boolean |
| Enables continuous automatic focus adjustments. The effect of manual focus adjustments while this feature is enabled is undefined, drivers should ignore such requests.
`V4L2_CID_AUTO_FOCUS_START` | button |
| Starts single auto focus process. The effect of setting this control when `V4L2_CID_FOCUS_AUTO` is set to `TRUE` (1) is undefined, drivers should ignore such requests.
`V4L2_CID_AUTO_FOCUS_STOP` | button |
| Aborts automatic focusing started with `V4L2_CID_AUTO_FOCUS_START` control. It is effective only when the continuous autofocus is disabled, that is when `V4L2_CID_FOCUS_AUTO` control is set to `FALSE` (0).
`V4L2_CID_AUTO_FOCUS_STATUS` | bitmask |
| The automatic focus status. This is a read-only control.

`V4L2_AUTO_FOCUS_STATUS_IDLE` | Automatic focus is not active.
`V4L2_AUTO_FOCUS_STATUS_BUSY` | Automatic focusing is in progress.
`V4L2_AUTO_FOCUS_STATUS_REACHED` | Focus has been reached.
`V4L2_AUTO_FOCUS_STATUS_FAILED` | Automatic focus has failed, the driver will not transition from this state until another action is performed by an application.

| Setting `V4L2_LOCK_FOCUS` lock bit of the `V4L2_CID_3A_LOCK` control may stop updates of the `V4L2_CID_AUTO_FOCUS_STATUS` control value.
`V4L2_CID_AUTO_FOCUS_RANGE` | enum v4l2_auto_focus_range |
| Determines auto focus distance range for which lens may be adjusted.

`V4L2_AUTO_FOCUS_RANGE_AUTO` | The camera automatically selects the focus range.
`V4L2_AUTO_FOCUS_RANGE_NORMAL` | Normal distance range, limited for best automatic focus performance.
`V4L2_AUTO_FOCUS_RANGE_MACRO` | Macro (close-up) auto focus. The camera will use its minimum possible distance for auto focus.
`V4L2_AUTO_FOCUS_RANGE_INFINITY` | The lens is set to focus on an object at infinite distance.

`V4L2_CID_ZOOM_ABSOLUTE` | integer |
| Specify the objective lens focal length as an absolute value. The zoom unit is driver-specific and its value should be a positive integer.
`V4L2_CID_ZOOM_RELATIVE` | integer |
| Specify the objective lens focal length relatively to the current value. Positive values move the zoom lens group towards the telephoto direction, negative values towards the wide-angle direction. The zoom unit is driver-specific. This is a write-only control.
`V4L2_CID_ZOOM_CONTINUOUS` | integer |
| Move the objective lens group at the specified speed until it reaches physical device limits or until an explicit request to stop the movement. A positive value moves the zoom lens group towards the telephoto direction. A value of zero stops the zoom lens group movement. A negative value moves the zoom lens group towards the wide-angle direction. The zoom speed unit is driver-specific.
`V4L2_CID_IRIS_ABSOLUTE` | integer |
| This control sets the camera's aperture to the specified value. The unit is undefined. Larger values open the iris wider, smaller values close it.
`V4L2_CID_IRIS_RELATIVE` | integer |
| This control modifies the camera's aperture by the specified amount. The unit is undefined. Positive values open the iris one step further, negative values close it one step further. This is a write-only control.
`V4L2_CID_PRIVACY` | boolean |
| Prevent video from being acquired by the camera. When this control is set to `TRUE` (1), no image can be captured by the camera. Common means to enforce privacy are mechanical obturation of the sensor and firmware image processing, but the device is not restricted to these methods. Devices that implement the privacy control must support read access and may support write access.
`V4L2_CID_BAND_STOP_FILTER` | integer |
| Switch the band-stop filter of a camera sensor on or off, or specify its strength. Such band-stop filters can be used, for example, to filter out the fluorescent light component.
`V4L2_CID_AUTO_N_PRESET_WHITE_BALANCE` | enum v4l2_auto_n_preset_white_balance |
| Sets white balance to automatic, manual or a preset. The presets determine color temperature of the light as a hint to the camera for white balance adjustments resulting in most accurate color representation. The following white balance presets are listed in order of increasing color temperature.

`V4L2_WHITE_BALANCE_MANUAL` | Manual white balance.
`V4L2_WHITE_BALANCE_AUTO` | Automatic white balance adjustments.
`V4L2_WHITE_BALANCE_INCANDESCENT` | White balance setting for incandescent (tungsten) lighting. It generally cools down the colors and corresponds approximately to 2500...3500 K color temperature range.
`V4L2_WHITE_BALANCE_FLUORESCENT` | White balance preset for fluorescent lighting. It corresponds approximately to 4000...5000 K color temperature.
`V4L2_WHITE_BALANCE_FLUORESCENT_H` | With this setting the camera will compensate for fluorescent H lighting.
`V4L2_WHITE_BALANCE_HORIZON` | White balance setting for horizon daylight. It corresponds approximately to 5000 K color temperature.
`V4L2_WHITE_BALANCE_DAYLIGHT` | White balance preset for daylight (with clear sky). It corresponds approximately to 5000...6500 K color temperature.
`V4L2_WHITE_BALANCE_FLASH` | With this setting the camera will compensate for the flash light. It slightly warms up the colors and corresponds roughly to 5000...5500 K color temperature.
`V4L2_WHITE_BALANCE_CLOUDY` | White balance preset for moderately overcast sky. This option corresponds approximately to 6500...8000 K color temperature range.
`V4L2_WHITE_BALANCE_SHADE` | White balance preset for shade or heavily overcast sky. It corresponds approximately to 9000...10000 K color temperature.

`V4L2_CID_WIDE_DYNAMIC_RANGE` | boolean |
| Enables or disables the camera's wide dynamic range feature. This feature allows to obtain clear images in situations where intensity of the illumination varies significantly throughout the scene, i.e. there are simultaneously very dark and very bright areas. It is most commonly realized in cameras by combining two subsequent frames with different exposure times. [a]
`V4L2_CID_IMAGE_STABILIZATION` | boolean |
| Enables or disables image stabilization. [a]
`V4L2_CID_ISO_SENSITIVITY` | integer menu |

Determines ISO equivalent of an image sensor indicating the sensor's sensitivity to light. The numbers are expressed in arithmetic scale, as per [ISO 12232:2006] standard, where doubling the sensor sensitivity is represented by doubling the numerical ISO value. Applications should interpret the values as standard ISO values multiplied by 1000, e.g. control value 800 stands for ISO 0.8. Drivers will usually support only a subset of standard ISO values. The effect of setting this control while the `V4L2_CID_ISO_SENSITIVITY_AUTO` control is set to a value other than `V4L2_CID_ISO_SENSITIVITY_MANUAL` is undefined, drivers should ignore such requests.

`V4L2_CID_ISO_SENSITIVITY_AUTO` | enum v4l2_iso_sensitivity_type |
| Enables or disables automatic ISO sensitivity adjustments.

`V4L2_CID_ISO_SENSITIVITY_MANUAL` | Manual ISO sensitivity.
`V4L2_CID_ISO_SENSITIVITY_AUTO` | Automatic ISO sensitivity adjustments.

`V4L2_CID_SCENE_MODE` | enum v4l2_scene_mode |

This control allows to select scene programs as the camera automatic modes optimized for common shooting scenes. Within these modes the camera determines best exposure, aperture, focusing, light metering, white balance and equivalent sensitivity. The controls of those parameters are influenced by the scene mode control. An exact behavior in each mode is subject to the camera specification.

When the scene mode feature is not used, this control should be set to `V4L2_SCENE_MODE_NONE` to make sure the other possibly related controls are accessible. The following scene programs are defined:

`V4L2_SCENE_MODE_NONE` | The scene mode feature is disabled.
`V4L2_SCENE_MODE_BACKLIGHT` | Backlight. Compensates for dark shadows when light is coming from behind a subject, also by automatically turning on the flash.

`V4L2_SCENE_MODE_BEACH_SNOW`

Beach and snow. This mode compensates for all-white or bright scenes, which tend to look gray and low contrast, when camera's automatic exposure is based on an average scene brightness. To compensate, this mode automatically slightly overexposes the frames. The white balance may also be adjusted to compensate for the fact that reflected snow looks bluish rather than white.

`V4L2_SCENE_MODE_CANDLELIGHT` | Candle light. The camera generally raises the ISO sensitivity and lowers the shutter speed. This mode compensates for relatively close subject in the scene. The flash is disabled in order to preserve the ambiance of the light.
`V4L2_SCENE_MODE_DAWN_DUSK` | Dawn and dusk. Preserves the colors seen in low natural light before dusk and after down. The camera may turn off the flash, and automatically focus at infinity. It will usually boost saturation and lower the shutter speed.
`V4L2_SCENE_MODE_FALL_COLORS` | Fall colors. Increases saturation and adjusts white balance for color enhancement. Pictures of autumn leaves get saturated reds and yellows.
`V4L2_SCENE_MODE_FIREWORKS` | Fireworks. Long exposure times are used to capture the expanding burst of light from a firework. The camera may invoke image stabilization.
`V4L2_SCENE_MODE_LANDSCAPE` | Landscape. The camera may choose a small aperture to provide deep depth of field and long exposure duration to help capture detail in dim light conditions. The focus is fixed at infinity. Suitable for distant and wide scenery.
`V4L2_SCENE_MODE_NIGHT` | Night, also known as Night Landscape. Designed for low light conditions, it preserves detail in the dark areas without blowing out bright objects. The camera generally sets itself to a medium-to-high ISO sensitivity, with a relatively long exposure time, and turns flash off. As such, there will be increased image noise and the possibility of blurred image.
`V4L2_SCENE_MODE_PARTY_INDOOR` | Party and indoor. Designed to capture indoor scenes that are lit by indoor background lighting as well as the flash. The camera usually increases ISO sensitivity, and adjusts exposure for the low light conditions.
`V4L2_SCENE_MODE_PORTRAIT` | Portrait. The camera adjusts the aperture so that the depth of field is reduced, which helps to isolate the subject against a smooth background. Most cameras recognize the presence of faces in the scene and focus on them. The color hue is adjusted to enhance skin tones. The intensity of the flash is often reduced.
`V4L2_SCENE_MODE_SPORTS` | Sports. Significantly increases ISO and uses a fast shutter speed to freeze motion of rapidly-moving subjects. Increased image noise may be seen in this mode.
`V4L2_SCENE_MODE_SUNSET` | Sunset. Preserves deep hues seen in sunsets and sunrises. It bumps up the saturation.
`V4L2_SCENE_MODE_TEXT` | Text. It applies extra contrast and sharpness, it is typically a black-and-white mode optimized for readability. Automatic focus may be switched to close-up mode and this setting may also involve some lens-distortion correction.

`V4L2_CID_3A_LOCK` | bitmask |
| This control locks or unlocks the automatic focus, exposure and white balance. The automatic adjustments can be paused independently by setting the corresponding lock bit to 1. The camera then retains the settings until the lock bit is cleared. The following lock bits are defined:

`V4L2_LOCK_EXPOSURE` | Automatic exposure adjustments lock.
`V4L2_LOCK_WHITE_BALANCE` | Automatic white balance adjustments lock.
`V4L2_LOCK_FOCUS` | Automatic focus lock.

| When a given algorithm is not enabled, drivers should ignore requests to lock it and should return no error. An example might be an application setting bit `V4L2_LOCK_WHITE_BALANCE` when the `V4L2_CID_AUTO_WHITE_BALANCE` control is set to `FALSE`. The value of this control may be changed by exposure, white balance or focus controls.
[a] This control may be changed to a menu control in the future, if more options are required.

### FM Transmitter Control Reference

The FM Transmitter (FM_TX) class includes controls for common features of FM transmissions capable devices. Currently this class includes parameters for audio compression, pilot tone generation, audio deviation limiter, RDS transmission and tuning power features.

Table 1.7. FM_TX Control IDs

ID | Type |
| Description
`V4L2_CID_FM_TX_CLASS` | class |
| The FM_TX class descriptor. Calling `VIDIOC_QUERYCTRL` for this control will return a description of this control class.
`V4L2_CID_RDS_TX_DEVIATION` | integer |
| Configures RDS signal frequency deviation level in Hz. The range and step are driver-specific.
`V4L2_CID_RDS_TX_PI` | integer |
| Sets the RDS Programme Identification field for transmission.
`V4L2_CID_RDS_TX_PTY` | integer |
| Sets the RDS Programme Type field for transmission. This encodes up to 31 pre-defined programme types.
`V4L2_CID_RDS_TX_PS_NAME` | string |

Sets the Programme Service name (PS_NAME) for transmission. It is intended for static display on a receiver. It is the primary aid to listeners in programme service identification and selection. In Annex E of [IEC 62106], the RDS specification, there is a full description of the correct character encoding for Programme Service name strings. Also from RDS specification, PS is usually a single eight character text. However, it is also possible to find receivers which can scroll strings sized as 8 x N characters. So, this control must be configured with steps of 8 characters. The result is it must always contain a string with size multiple of 8.

`V4L2_CID_RDS_TX_RADIO_TEXT` | string |

Sets the Radio Text info for transmission. It is a textual description of what is being broadcasted. RDS Radio Text can be applied when broadcaster wishes to transmit longer PS names, programme-related information or any other text. In these cases, RadioText should be used in addition to `V4L2_CID_RDS_TX_PS_NAME`. The encoding for Radio Text strings is also fully described in Annex E of [IEC 62106]. The length of Radio Text strings depends on which RDS Block is being used to transmit it, either 32 (2A block) or 64 (2B block). However, it is also possible to find receivers which can scroll strings sized as 32 x N or 64 x N characters. So, this control must be configured with steps of 32 or 64 characters. The result is it must always contain a string with size multiple of 32 or 64.

`V4L2_CID_AUDIO_LIMITER_ENABLED` | boolean |
| Enables or disables the audio deviation limiter feature. The limiter is useful when trying to maximize the audio volume, minimize receiver-generated distortion and prevent overmodulation.
`V4L2_CID_AUDIO_LIMITER_RELEASE_TIME` | integer |
| Sets the audio deviation limiter feature release time. Unit is in useconds. Step and range are driver-specific.
`V4L2_CID_AUDIO_LIMITER_DEVIATION` | integer |
| Configures audio frequency deviation level in Hz. The range and step are driver-specific.
`V4L2_CID_AUDIO_COMPRESSION_ENABLED` | boolean |
| Enables or disables the audio compression feature. This feature amplifies signals below the threshold by a fixed gain and compresses audio signals above the threshold by the ratio of Threshold/(Gain + Threshold).
`V4L2_CID_AUDIO_COMPRESSION_GAIN` | integer |
| Sets the gain for audio compression feature. It is a dB value. The range and step are driver-specific.
`V4L2_CID_AUDIO_COMPRESSION_THRESHOLD` | integer |
| Sets the threshold level for audio compression freature. It is a dB value. The range and step are driver-specific.
`V4L2_CID_AUDIO_COMPRESSION_ATTACK_TIME` | integer |
| Sets the attack time for audio compression feature. It is a useconds value. The range and step are driver-specific.
`V4L2_CID_AUDIO_COMPRESSION_RELEASE_TIME` | integer |
| Sets the release time for audio compression feature. It is a useconds value. The range and step are driver-specific.
`V4L2_CID_PILOT_TONE_ENABLED` | boolean |
| Enables or disables the pilot tone generation feature.
`V4L2_CID_PILOT_TONE_DEVIATION` | integer |
| Configures pilot tone frequency deviation level. Unit is in Hz. The range and step are driver-specific.
`V4L2_CID_PILOT_TONE_FREQUENCY` | integer |
| Configures pilot tone frequency value. Unit is in Hz. The range and step are driver-specific.
`V4L2_CID_TUNE_PREEMPHASIS` | enum v4l2_preemphasis |
| Configures the pre-emphasis value for broadcasting. A pre-emphasis filter is applied to the broadcast to accentuate the high audio frequencies. Depending on the region, a time constant of either 50 or 75 useconds is used. The enum v4l2_preemphasis defines possible values for pre-emphasis. Here they are:

`V4L2_PREEMPHASIS_DISABLED` | No pre-emphasis is applied.
`V4L2_PREEMPHASIS_50_uS` | A pre-emphasis of 50 uS is used.
`V4L2_PREEMPHASIS_75_uS` | A pre-emphasis of 75 uS is used.

`V4L2_CID_TUNE_POWER_LEVEL` | integer |
| Sets the output power level for signal transmission. Unit is in dBuV. Range and step are driver-specific.
`V4L2_CID_TUNE_ANTENNA_CAPACITOR` | integer |
| This selects the value of antenna tuning capacitor manually or automatically if set to zero. Unit, range and step are driver-specific.

For more details about RDS specification, refer to [IEC 62106] document, from CENELEC.

### Flash Control Reference

### Experimental

This is an experimental interface and may change in the future.

The V4L2 flash controls are intended to provide generic access to flash controller devices. Flash controller devices are typically used in digital cameras.

The interface can support both LED and xenon flash devices. As of writing this, there is no xenon flash driver using this interface.

#### Supported use cases

##### Unsynchronised LED flash (software strobe)

Unsynchronised LED flash is controlled directly by the host as the sensor. The flash must be enabled by the host before the exposure of the image starts and disabled once it ends. The host is fully responsible for the timing of the flash.

Example of such device: Nokia N900.

##### Synchronised LED flash (hardware strobe)

The synchronised LED flash is pre-programmed by the host (power and timeout) but controlled by the sensor through a strobe signal from the sensor to the flash.

The sensor controls the flash duration and timing. This information typically must be made available to the sensor.

##### LED flash as torch

LED flash may be used as torch in conjunction with another use case involving camera or individually.

Table 1.8. Flash Control IDs

ID | Type |
| Description
`V4L2_CID_FLASH_CLASS` | class |
| The FLASH class descriptor.
`V4L2_CID_FLASH_LED_MODE` | menu |
| Defines the mode of the flash LED, the high-power white LED attached to the flash controller. Setting this control may not be possible in presence of some faults. See V4L2_CID_FLASH_FAULT.

`V4L2_FLASH_LED_MODE_NONE` | Off.
`V4L2_FLASH_LED_MODE_FLASH` | Flash mode.
`V4L2_FLASH_LED_MODE_TORCH` | Torch mode. See V4L2_CID_FLASH_TORCH_INTENSITY.

`V4L2_CID_FLASH_STROBE_SOURCE` | menu |
| Defines the source of the flash LED strobe.

`V4L2_FLASH_STROBE_SOURCE_SOFTWARE` | The flash strobe is triggered by using the V4L2_CID_FLASH_STROBE control.
`V4L2_FLASH_STROBE_SOURCE_EXTERNAL` | The flash strobe is triggered by an external source. Typically this is a sensor, which makes it possible to synchronises the flash strobe start to exposure start.

`V4L2_CID_FLASH_STROBE` | button |
| Strobe flash. Valid when V4L2_CID_FLASH_LED_MODE is set to V4L2_FLASH_LED_MODE_FLASH and V4L2_CID_FLASH_STROBE_SOURCE is set to V4L2_FLASH_STROBE_SOURCE_SOFTWARE. Setting this control may not be possible in presence of some faults. See V4L2_CID_FLASH_FAULT.
`V4L2_CID_FLASH_STROBE_STOP` | button |
| Stop flash strobe immediately.
`V4L2_CID_FLASH_STROBE_STATUS` | boolean |
| Strobe status: whether the flash is strobing at the moment or not. This is a read-only control.
`V4L2_CID_FLASH_TIMEOUT` | integer |
| Hardware timeout for flash. The flash strobe is stopped after this period of time has passed from the start of the strobe.
`V4L2_CID_FLASH_INTENSITY` | integer |
| Intensity of the flash strobe when the flash LED is in flash mode (V4L2_FLASH_LED_MODE_FLASH). The unit should be milliamps (mA) if possible.
`V4L2_CID_FLASH_TORCH_INTENSITY` | integer |
| Intensity of the flash LED in torch mode (V4L2_FLASH_LED_MODE_TORCH). The unit should be milliamps (mA) if possible. Setting this control may not be possible in presence of some faults. See V4L2_CID_FLASH_FAULT.
`V4L2_CID_FLASH_INDICATOR_INTENSITY` | integer |
| Intensity of the indicator LED. The indicator LED may be fully independent of the flash LED. The unit should be microamps (uA) if possible.
`V4L2_CID_FLASH_FAULT` | bitmask |

Faults related to the flash. The faults tell about specific problems in the flash chip itself or the LEDs attached to it. Faults may prevent further use of some of the flash controls. In particular, V4L2_CID_FLASH_LED_MODE is set to V4L2_FLASH_LED_MODE_NONE if the fault affects the flash LED. Exactly which faults have such an effect is chip dependent. Reading the faults resets the control and returns the chip to a usable state if possible.

`V4L2_FLASH_FAULT_OVER_VOLTAGE` | Flash controller voltage to the flash LED has exceeded the limit specific to the flash controller.
`V4L2_FLASH_FAULT_TIMEOUT` | The flash strobe was still on when the timeout set by the user --- V4L2_CID_FLASH_TIMEOUT control --- has expired. Not all flash controllers may set this in all such conditions.
`V4L2_FLASH_FAULT_OVER_TEMPERATURE` | The flash controller has overheated.
`V4L2_FLASH_FAULT_SHORT_CIRCUIT` | The short circuit protection of the flash controller has been triggered.
`V4L2_FLASH_FAULT_OVER_CURRENT` | Current in the LED power supply has exceeded the limit specific to the flash controller.
`V4L2_FLASH_FAULT_INDICATOR` | The flash controller has detected a short or open circuit condition on the indicator LED.

`V4L2_CID_FLASH_CHARGE` | boolean |
| Enable or disable charging of the xenon flash capacitor.
`V4L2_CID_FLASH_READY` | boolean |
| Is the flash ready to strobe? Xenon flashes require their capacitors charged before strobing. LED flashes often require a cooldown period after strobe during which another strobe will not be possible. This is a read-only control.

### JPEG Control Reference

The JPEG class includes controls for common features of JPEG encoders and decoders. Currently it includes features for codecs implementing progressive baseline DCT compression process with Huffman entrophy coding.

Table 1.9. JPEG Control IDs

ID | Type |
| Description
`V4L2_CID_JPEG_CLASS` | class |
| The JPEG class descriptor. Calling `VIDIOC_QUERYCTRL` for this control will return a description of this control class.
`V4L2_CID_JPEG_CHROMA_SUBSAMPLING` | menu |
| The chroma subsampling factors describe how each component of an input image is sampled, in respect to maximum sample rate in each spatial dimension. See [ITU-T.81], clause A.1.1. for more details. The `V4L2_CID_JPEG_CHROMA_SUBSAMPLING` control determines how Cb and Cr components are downsampled after coverting an input image from RGB to Y'CbCr color space.

`V4L2_JPEG_CHROMA_SUBSAMPLING_444` | No chroma subsampling, each pixel has Y, Cr and Cb values.
`V4L2_JPEG_CHROMA_SUBSAMPLING_422` | Horizontally subsample Cr, Cb components by a factor of 2.
`V4L2_JPEG_CHROMA_SUBSAMPLING_420` | Subsample Cr, Cb components horizontally and vertically by 2.
`V4L2_JPEG_CHROMA_SUBSAMPLING_411` | Horizontally subsample Cr, Cb components by a factor of 4.
`V4L2_JPEG_CHROMA_SUBSAMPLING_410` | Subsample Cr, Cb components horizontally by 4 and vertically by 2.
`V4L2_JPEG_CHROMA_SUBSAMPLING_GRAY` | Use only luminance component.

`V4L2_CID_JPEG_RESTART_INTERVAL` | integer |

The restart interval determines an interval of inserting RSTm markers (m = 0..7). The purpose of these markers is to additionally reinitialize the encoder process, in order to process blocks of an image independently. For the lossy compression processes the restart interval unit is MCU (Minimum Coded Unit) and its value is contained in DRI (Define Restart Interval) marker. If `V4L2_CID_JPEG_RESTART_INTERVAL` control is set to 0, DRI and RSTm markers will not be inserted.

`V4L2_CID_JPEG_COMPRESSION_QUALITY` | integer |

`V4L2_CID_JPEG_COMPRESSION_QUALITY` control determines trade-off between image quality and size. It provides simpler method for applications to control image quality, without a need for direct reconfiguration of luminance and chrominance quantization tables. In cases where a driver uses quantization tables configured directly by an application, using interfaces defined elsewhere, `V4L2_CID_JPEG_COMPRESSION_QUALITY` control should be set by driver to 0.

The value range of this control is driver-specific. Only positive, non-zero values are meaningful. The recommended range is 1 - 100, where larger values correspond to better image quality.

`V4L2_CID_JPEG_ACTIVE_MARKER` | bitmask |
| Specify which JPEG markers are included in compressed stream. This control is valid only for encoders.

`V4L2_JPEG_ACTIVE_MARKER_APP0` | Application data segment APP0.
`V4L2_JPEG_ACTIVE_MARKER_APP1` | Application data segment APP1.
`V4L2_JPEG_ACTIVE_MARKER_COM` | Comment segment.
`V4L2_JPEG_ACTIVE_MARKER_DQT` | Quantization tables segment.
`V4L2_JPEG_ACTIVE_MARKER_DHT` | Huffman tables segment.

For more details about JPEG specification, refer to [ITU-T.81], [JFIF], [W3C JPEG JFIF].

### Image Source Control Reference

### Experimental

This is an experimental interface and may change in the future.

The Image Source control class is intended for low-level control of image source devices such as image sensors. The devices feature an analogue to digital converter and a bus transmitter to transmit the image data out of the device.

Table 1.10. Image Source Control IDs

ID | Type |
| Description
`V4L2_CID_IMAGE_SOURCE_CLASS` | class |
| The IMAGE_SOURCE class descriptor.
`V4L2_CID_VBLANK` | integer |
| Vertical blanking. The idle period after every frame during which no image data is produced. The unit of vertical blanking is a line. Every line has length of the image width plus horizontal blanking at the pixel rate defined by `V4L2_CID_PIXEL_RATE` control in the same sub-device.
`V4L2_CID_HBLANK` | integer |
| Horizontal blanking. The idle period after every line of image data during which no image data is produced. The unit of horizontal blanking is pixels.
`V4L2_CID_ANALOGUE_GAIN` | integer |
| Analogue gain is gain affecting all colour components in the pixel matrix. The gain operation is performed in the analogue domain before A/D conversion.

### Image Process Control Reference

### Experimental

This is an experimental interface and may change in the future.

The Image Source control class is intended for low-level control of image processing functions. Unlike `V4L2_CID_IMAGE_SOURCE_CLASS`, the controls in this class affect processing the image, and do not control capturing of it.

Table 1.11. Image Source Control IDs

ID | Type |
| Description
`V4L2_CID_IMAGE_PROC_CLASS` | class |
| The IMAGE_PROC class descriptor.
`V4L2_CID_LINK_FREQ` | integer menu |

Data bus frequency. Together with the media bus pixel code, bus type (clock cycles per sample), the data bus frequency defines the pixel rate (`V4L2_CID_PIXEL_RATE`) in the pixel array (or possibly elsewhere, if the device is not an image sensor). The frame rate can be calculated from the pixel clock, image width and height and horizontal and vertical blanking. While the pixel rate control may be defined elsewhere than in the subdev containing the pixel array, the frame rate cannot be obtained from that information. This is because only on the pixel array it can be assumed that the vertical and horizontal blanking information is exact: no other blanking is allowed in the pixel array. The selection of frame rate is performed by selecting the desired horizontal and vertical blanking. The unit of this control is Hz.

`V4L2_CID_PIXEL_RATE` | 64-bit integer |
| Pixel rate in the source pads of the subdev. This control is read-only and its unit is pixels / second.
`V4L2_CID_TEST_PATTERN` | menu |
| Some capture/display/sensor devices have the capability to generate test pattern images. These hardware specific test patterns can be used to test if a device is working properly.

### Digital Video Control Reference

### Experimental

This is an experimental interface and may change in the future.

The Digital Video control class is intended to control receivers and transmitters for VGA, DVI (Digital Visual Interface), HDMI ([HDMI]) and DisplayPort ([DP]). These controls are generally expected to be private to the receiver or transmitter subdevice that implements them, so they are only exposed on the `/dev/v4l-subdev*` device node.

Note that these devices can have multiple input or output pads which are hooked up to e.g. HDMI connectors. Even though the subdevice will receive or transmit video from/to only one of those pads, the other pads can still be active when it comes to EDID (Extended Display Identification Data, [EDID]) and HDCP (High-bandwidth Digital Content Protection System, [HDCP]) processing, allowing the device to do the fairly slow EDID/HDCP handling in advance. This allows for quick switching between connectors.

These pads appear in several of the controls in this section as bitmasks, one bit for each pad. Bit 0 corresponds to pad 0, bit 1 to pad 1, etc. The maximum value of the control is the set of valid pads.

Table 1.12. Digital Video Control IDs

ID | Type |
| Description
`V4L2_CID_DV_CLASS` | class |
| The Digital Video class descriptor.
`V4L2_CID_DV_TX_HOTPLUG` | bitmask |

Many connectors have a hotplug pin which is high if EDID information is available from the source. This control shows the state of the hotplug pin as seen by the transmitter. Each bit corresponds to an output pad on the transmitter. If an output pad does not have an associated hotplug pin, then the bit for that pad will be 0. This read-only control is applicable to DVI-D, HDMI and DisplayPort connectors.

`V4L2_CID_DV_TX_RXSENSE` | bitmask |

Rx Sense is the detection of pull-ups on the TMDS clock lines. This normally means that the sink has left/entered standby (i.e. the transmitter can sense that the receiver is ready to receive video). Each bit corresponds to an output pad on the transmitter. If an output pad does not have an associated Rx Sense, then the bit for that pad will be 0. This read-only control is applicable to DVI-D and HDMI devices.

`V4L2_CID_DV_TX_EDID_PRESENT` | bitmask |
| When the transmitter sees the hotplug signal from the receiver it will attempt to read the EDID. If set, then the transmitter has read at least the first block (= 128 bytes). Each bit corresponds to an output pad on the transmitter. If an output pad does not support EDIDs, then the bit for that pad will be 0. This read-only control is applicable to VGA, DVI-A/D, HDMI and DisplayPort connectors.
`V4L2_CID_DV_TX_MODE` | enum v4l2_dv_tx_mode |
| HDMI transmitters can transmit in DVI-D mode (just video) or in HDMI mode (video + audio + auxiliary data). This control selects which mode to use: V4L2_DV_TX_MODE_DVI_D or V4L2_DV_TX_MODE_HDMI. This control is applicable to HDMI connectors.
`V4L2_CID_DV_TX_RGB_RANGE` | enum v4l2_dv_rgb_range |

Select the quantization range for RGB output. V4L2_DV_RANGE_AUTO follows the RGB quantization range specified in the standard for the video interface (ie. [CEA-861-E] for HDMI). V4L2_DV_RANGE_LIMITED and V4L2_DV_RANGE_FULL override the standard to be compatible with sinks that have not implemented the standard correctly (unfortunately quite common for HDMI and DVI-D). Full range allows all possible values to be used whereas limited range sets the range to (16 << (N-8)) - (235 << (N-8)) where N is the number of bits per component. This control is applicable to VGA, DVI-A/D, HDMI and DisplayPort connectors.

`V4L2_CID_DV_RX_POWER_PRESENT` | bitmask |

Detects whether the receiver receives power from the source (e.g. HDMI carries 5V on one of the pins). This is often used to power an eeprom which contains EDID information, such that the source can read the EDID even if the sink is in standby/power off. Each bit corresponds to an input pad on the transmitter. If an input pad cannot detect whether power is present, then the bit for that pad will be 0. This read-only control is applicable to DVI-D, HDMI and DisplayPort connectors.

`V4L2_CID_DV_RX_RGB_RANGE` | enum v4l2_dv_rgb_range |

Select the quantization range for RGB input. V4L2_DV_RANGE_AUTO follows the RGB quantization range specified in the standard for the video interface (ie. [CEA-861-E] for HDMI). V4L2_DV_RANGE_LIMITED and V4L2_DV_RANGE_FULL override the standard to be compatible with sources that have not implemented the standard correctly (unfortunately quite common for HDMI and DVI-D). Full range allows all possible values to be used whereas limited range sets the range to (16 << (N-8)) - (235 << (N-8)) where N is the number of bits per component. This control is applicable to VGA, DVI-A/D, HDMI and DisplayPort connectors.

### FM Receiver Control Reference

The FM Receiver (FM_RX) class includes controls for common features of FM Reception capable devices.

Table 1.13. FM_RX Control IDs

ID | Type |
| Description
`V4L2_CID_FM_RX_CLASS` | class |
| The FM_RX class descriptor. Calling `VIDIOC_QUERYCTRL` for this control will return a description of this control class.
`V4L2_CID_RDS_RECEPTION` | boolean |
| Enables/disables RDS reception by the radio tuner
`V4L2_CID_TUNE_DEEMPHASIS` | enum v4l2_deemphasis |
| Configures the de-emphasis value for reception. A de-emphasis filter is applied to the broadcast to accentuate the high audio frequencies. Depending on the region, a time constant of either 50 or 75 useconds is used. The enum v4l2_deemphasis defines possible values for de-emphasis. Here they are:

`V4L2_DEEMPHASIS_DISABLED` | No de-emphasis is applied.
`V4L2_DEEMPHASIS_50_uS` | A de-emphasis of 50 uS is used.
`V4L2_DEEMPHASIS_75_uS` | A de-emphasis of 75 uS is used.

Prev | Up | Next
User Controls | Home | Data Formats