## GstAudioDownmixMeta

GstAudioDownmixMeta — Buffer metadata for audio downmix matrix handling

## Functions

GstAudioDownmixMeta * | gst_buffer_add_audio_downmix_meta ()
#define | gst_buffer_get_audio_downmix_meta()
GstAudioDownmixMeta * | gst_buffer_get_audio_downmix_meta_for_channels ()
GstAudioClippingMeta * | gst_buffer_add_audio_clipping_meta ()
#define | gst_buffer_get_audio_clipping_meta()

## Types and Values

struct | GstAudioDownmixMeta
struct | GstAudioClippingMeta

## Includes

    #include <gst/audio/gstaudiometa.h>

## Description

GstAudioDownmixMeta defines an audio downmix matrix to be send along with audio buffers. These functions in this module help to create and attach the meta as well as extracting it.

## Functions

### gst_buffer_add_audio_downmix_meta ()

    GstAudioDownmixMeta *
    gst_buffer_add_audio_downmix_meta (GstBuffer *buffer,
                                       const GstAudioChannelPosition *from_position,
                                       gint from_channels,
                                       const GstAudioChannelPosition *to_position,
                                       gint to_channels,
                                       const gfloat **matrix);

Attaches GstAudioDownmixMeta metadata to `buffer` with the given parameters.

`matrix` is an two-dimensional array of `to_channels` times `from_channels` coefficients, i.e. the i-th output channels is constructed by multiplicating the input channels with the coefficients in `matrix` [i] and taking the sum of the results.

#### Parameters

buffer | a GstBuffer |
from_position | the channel positions of the source. | [array length=from_channels]
from_channels | The number of channels of the source |
to_position | the channel positions of the destination. | [array length=to_channels]
to_channels | The number of channels of the destination |
matrix | The matrix coefficients. |

#### Returns

the GstAudioDownmixMeta on `buffer` .

[transfer none]

### gst_buffer_get_audio_downmix_meta()

    #define gst_buffer_get_audio_downmix_meta(b) ((GstAudioDownmixMeta*)gst_buffer_get_meta((b), GST_AUDIO_DOWNMIX_META_API_TYPE))

### gst_buffer_get_audio_downmix_meta_for_channels ()

    GstAudioDownmixMeta *
    gst_buffer_get_audio_downmix_meta_for_channels
                                   (GstBuffer *buffer,
                                    const GstAudioChannelPosition *to_position,
                                    gint to_channels);

Find the GstAudioDownmixMeta on `buffer` for the given destination channel positions.

#### Parameters

buffer | a GstBuffer |
to_position | the channel positions of the destination. | [array length=to_channels]
to_channels | The number of channels of the destination |

#### Returns

the GstAudioDownmixMeta on `buffer` .

[transfer none]

### gst_buffer_add_audio_clipping_meta ()

    GstAudioClippingMeta *
    gst_buffer_add_audio_clipping_meta (GstBuffer *buffer,
                                        GstFormat format,
                                        guint64 start,
                                        guint64 end);

Attaches GstAudioClippingMeta metadata to `buffer` with the given parameters.

#### Parameters

buffer | a GstBuffer |
format | GstFormat of `start` and `stop` , GST_FORMAT_DEFAULT is samples |
start | Amount of audio to clip from start of buffer |
end | Amount of to clip from end of buffer |

#### Returns

the GstAudioClippingMeta on `buffer` .

[transfer none]

Since: 1.8

### gst_buffer_get_audio_clipping_meta()

    #define gst_buffer_get_audio_clipping_meta(b) ((GstAudioClippingMeta*)gst_buffer_get_meta((b), GST_AUDIO_CLIPPING_META_API_TYPE))

## Types and Values

### struct GstAudioDownmixMeta

    struct GstAudioDownmixMeta {
      GstMeta      meta;

      GstAudioChannelPosition *from_position;
      GstAudioChannelPosition *to_position;
      gint        from_channels, to_channels;
      gfloat       **matrix;
    };

Extra buffer metadata describing audio downmixing matrix. This metadata is attached to audio buffers and contains a matrix to downmix the buffer number of channels to `channels` .

`matrix` is an two-dimensional array of `to_channels` times `from_channels` coefficients, i.e. the i-th output channels is constructed by multiplicating the input channels with the coefficients in `matrix` [i] and taking the sum of the results.

#### Members

GstMeta `meta`; | parent GstMeta |
GstAudioChannelPosition *`from_position`; | the channel positions of the source |
GstAudioChannelPosition *`to_position`; | the channel positions of the destination |
gint `from_channels`; | the number of channels of the source |
gint `to_channels`; | the number of channels of the destination |
gfloat **`matrix`; | the matrix coefficients. |

### struct GstAudioClippingMeta

    struct GstAudioClippingMeta {
      GstMeta   meta;

      GstFormat format;
      guint64   start;
      guint64   end;
    };

Extra buffer metadata describing how much audio has to be clipped from the start or end of a buffer. This is used for compressed formats, where the first frame usually has some additional samples due to encoder and decoder delays, and the last frame usually has some additional samples to be able to fill the complete last frame.

This is used to ensure that decoded data in the end has the same amount of samples, and multiply decoded streams can be gaplessly concatenated.

Note: If clipping of the start is done by adjusting the segment, this meta has to be dropped from buffers as otherwise clipping could happen twice.

#### Members

GstMeta `meta`; | parent GstMeta |
GstFormat `format`; | GstFormat of `start` and `stop` , GST_FORMAT_DEFAULT is samples |
guint64 `start`; | Amount of audio to clip from start of buffer |
guint64 `end`; | Amount of to clip from end of buffer |

Since: 1.8