[FFmpeg-devel] [PATCH] Add a new channel layout API

Nicolas George george at nsup.org
Wed Oct 30 20:13:03 EET 2019


Paul B Mahol (12019-10-28):
> The new API is more extensible and allows for custom layouts.
> More accurate information is exported, eg for decoders that do not
> set a channel layout, lavc will not make one up for them.
> 
> Deprecate the old API working with just uint64_t bitmasks.
> 
> Original commit by Anton Khirnov <anton at khirnov.net>.
> Expanded and completed by Vittorio Giovara <vittorio.giovara at gmail.com>.
> Adapted for FFmpeg by Paul B Mahol <onemda at gmail.com>.
> 
> Signed-off-by: Anton Khirnov <anton at khirnov.net>
> Signed-off-by: Vittorio Giovara <vittorio.giovara at gmail.com>
> Signed-off-by: Paul B Mahol <onemda at gmail.com>
> ---
>  libavutil/channel_layout.c | 385 ++++++++++++++++++++++++++++------
>  libavutil/channel_layout.h | 411 ++++++++++++++++++++++++++++++++++---
>  libavutil/version.h        |   3 +
>  3 files changed, 709 insertions(+), 90 deletions(-)

Just a few quick remarks on the API itself for now. I did not read the
implementation carefully.

> diff --git a/libavutil/channel_layout.c b/libavutil/channel_layout.c
> index 3bd5ee29b7..9112af32a6 100644
> --- a/libavutil/channel_layout.c
> +++ b/libavutil/channel_layout.c
> @@ -37,75 +37,87 @@ struct channel_name {
>  };
>  
>  static const struct channel_name channel_names[] = {
> -     [0] = { "FL",        "front left"            },
> -     [1] = { "FR",        "front right"           },
> -     [2] = { "FC",        "front center"          },
> -     [3] = { "LFE",       "low frequency"         },
> -     [4] = { "BL",        "back left"             },
> -     [5] = { "BR",        "back right"            },
> -     [6] = { "FLC",       "front left-of-center"  },
> -     [7] = { "FRC",       "front right-of-center" },
> -     [8] = { "BC",        "back center"           },
> -     [9] = { "SL",        "side left"             },
> -    [10] = { "SR",        "side right"            },
> -    [11] = { "TC",        "top center"            },
> -    [12] = { "TFL",       "top front left"        },
> -    [13] = { "TFC",       "top front center"      },
> -    [14] = { "TFR",       "top front right"       },
> -    [15] = { "TBL",       "top back left"         },
> -    [16] = { "TBC",       "top back center"       },
> -    [17] = { "TBR",       "top back right"        },
> -    [29] = { "DL",        "downmix left"          },
> -    [30] = { "DR",        "downmix right"         },
> -    [31] = { "WL",        "wide left"             },
> -    [32] = { "WR",        "wide right"            },
> -    [33] = { "SDL",       "surround direct left"  },
> -    [34] = { "SDR",       "surround direct right" },
> -    [35] = { "LFE2",      "low frequency 2"       },
> +    [AV_CHAN_FRONT_LEFT              ] = { "FL" },
> +    [AV_CHAN_FRONT_RIGHT             ] = { "FR" },
> +    [AV_CHAN_FRONT_CENTER            ] = { "FC" },
> +    [AV_CHAN_LOW_FREQUENCY           ] = { "LFE" },
> +    [AV_CHAN_BACK_LEFT               ] = { "BL" },
> +    [AV_CHAN_BACK_RIGHT              ] = { "BR" },
> +    [AV_CHAN_FRONT_LEFT_OF_CENTER    ] = { "FLC" },
> +    [AV_CHAN_FRONT_RIGHT_OF_CENTER   ] = { "FRC" },
> +    [AV_CHAN_BACK_CENTER             ] = { "BC" },
> +    [AV_CHAN_SIDE_LEFT               ] = { "SL" },
> +    [AV_CHAN_SIDE_RIGHT              ] = { "SR" },
> +    [AV_CHAN_TOP_CENTER              ] = { "TC" },
> +    [AV_CHAN_TOP_FRONT_LEFT          ] = { "TFL" },
> +    [AV_CHAN_TOP_FRONT_CENTER        ] = { "TFC" },
> +    [AV_CHAN_TOP_FRONT_RIGHT         ] = { "TFR" },
> +    [AV_CHAN_TOP_BACK_LEFT           ] = { "TBL" },
> +    [AV_CHAN_TOP_BACK_CENTER         ] = { "TBC" },
> +    [AV_CHAN_TOP_BACK_RIGHT          ] = { "TBR" },
> +    [AV_CHAN_STEREO_LEFT             ] = { "DL" },
> +    [AV_CHAN_STEREO_RIGHT            ] = { "DR" },
> +    [AV_CHAN_WIDE_LEFT               ] = { "WL" },
> +    [AV_CHAN_WIDE_RIGHT              ] = { "WR" },
> +    [AV_CHAN_SURROUND_DIRECT_LEFT    ] = { "SDL" },
> +    [AV_CHAN_SURROUND_DIRECT_RIGHT   ] = { "SDR" },
> +    [AV_CHAN_LOW_FREQUENCY_2         ] = { "LFE2" },
> +    [AV_CHAN_SILENCE                 ] = { "PAD" },
>  };
>  
> -static const char *get_channel_name(int channel_id)
> +const char *av_channel_name(enum AVChannel channel_id)
>  {
>      if (channel_id < 0 || channel_id >= FF_ARRAY_ELEMS(channel_names))
>          return NULL;
>      return channel_names[channel_id].name;
>  }
>  
> +int av_channel_from_string(const char *str)
> +{
> +    for (int i = 0; i < FF_ARRAY_ELEMS(channel_names); i++) {
> +        if (channel_names[i].name && !strcmp(str, channel_names[i].name)) {
> +            return i;
> +        }
> +    }
> +    return AVERROR(EINVAL);
> +}
> +
>  static const struct {
>      const char *name;
> -    int         nb_channels;
> -    uint64_t     layout;
> +    AVChannelLayout layout;
>  } channel_layout_map[] = {
> -    { "mono",        1,  AV_CH_LAYOUT_MONO },
> -    { "stereo",      2,  AV_CH_LAYOUT_STEREO },
> -    { "2.1",         3,  AV_CH_LAYOUT_2POINT1 },
> -    { "3.0",         3,  AV_CH_LAYOUT_SURROUND },
> -    { "3.0(back)",   3,  AV_CH_LAYOUT_2_1 },
> -    { "4.0",         4,  AV_CH_LAYOUT_4POINT0 },
> -    { "quad",        4,  AV_CH_LAYOUT_QUAD },
> -    { "quad(side)",  4,  AV_CH_LAYOUT_2_2 },
> -    { "3.1",         4,  AV_CH_LAYOUT_3POINT1 },
> -    { "5.0",         5,  AV_CH_LAYOUT_5POINT0_BACK },
> -    { "5.0(side)",   5,  AV_CH_LAYOUT_5POINT0 },
> -    { "4.1",         5,  AV_CH_LAYOUT_4POINT1 },
> -    { "5.1",         6,  AV_CH_LAYOUT_5POINT1_BACK },
> -    { "5.1(side)",   6,  AV_CH_LAYOUT_5POINT1 },
> -    { "6.0",         6,  AV_CH_LAYOUT_6POINT0 },
> -    { "6.0(front)",  6,  AV_CH_LAYOUT_6POINT0_FRONT },
> -    { "hexagonal",   6,  AV_CH_LAYOUT_HEXAGONAL },
> -    { "6.1",         7,  AV_CH_LAYOUT_6POINT1 },
> -    { "6.1(back)",   7,  AV_CH_LAYOUT_6POINT1_BACK },
> -    { "6.1(front)",  7,  AV_CH_LAYOUT_6POINT1_FRONT },
> -    { "7.0",         7,  AV_CH_LAYOUT_7POINT0 },
> -    { "7.0(front)",  7,  AV_CH_LAYOUT_7POINT0_FRONT },
> -    { "7.1",         8,  AV_CH_LAYOUT_7POINT1 },
> -    { "7.1(wide)",   8,  AV_CH_LAYOUT_7POINT1_WIDE_BACK },
> -    { "7.1(wide-side)",   8,  AV_CH_LAYOUT_7POINT1_WIDE },
> -    { "octagonal",   8,  AV_CH_LAYOUT_OCTAGONAL },
> -    { "hexadecagonal", 16, AV_CH_LAYOUT_HEXADECAGONAL },
> -    { "downmix",     2,  AV_CH_LAYOUT_STEREO_DOWNMIX, },
> +    { "mono",           AV_CHANNEL_LAYOUT_MONO                },
> +    { "stereo",         AV_CHANNEL_LAYOUT_STEREO              },
> +    { "2.1",            AV_CHANNEL_LAYOUT_2POINT1             },
> +    { "3.0",            AV_CHANNEL_LAYOUT_SURROUND            },
> +    { "3.0(back)",      AV_CHANNEL_LAYOUT_2_1                 },
> +    { "4.0",            AV_CHANNEL_LAYOUT_4POINT0             },
> +    { "quad",           AV_CHANNEL_LAYOUT_QUAD                },
> +    { "quad(side)",     AV_CHANNEL_LAYOUT_2_2                 },
> +    { "3.1",            AV_CHANNEL_LAYOUT_3POINT1             },
> +    { "5.0",            AV_CHANNEL_LAYOUT_5POINT0_BACK        },
> +    { "5.0(side)",      AV_CHANNEL_LAYOUT_5POINT0             },
> +    { "4.1",            AV_CHANNEL_LAYOUT_4POINT1             },
> +    { "5.1",            AV_CHANNEL_LAYOUT_5POINT1_BACK        },
> +    { "5.1(side)",      AV_CHANNEL_LAYOUT_5POINT1             },
> +    { "6.0",            AV_CHANNEL_LAYOUT_6POINT0             },
> +    { "6.0(front)",     AV_CHANNEL_LAYOUT_6POINT0_FRONT       },
> +    { "hexagonal",      AV_CHANNEL_LAYOUT_HEXAGONAL           },
> +    { "6.1",            AV_CHANNEL_LAYOUT_6POINT1             },
> +    { "6.1(back)",      AV_CHANNEL_LAYOUT_6POINT1_BACK        },
> +    { "6.1(front)",     AV_CHANNEL_LAYOUT_6POINT1_FRONT       },
> +    { "7.0",            AV_CHANNEL_LAYOUT_7POINT0             },
> +    { "7.0(front)",     AV_CHANNEL_LAYOUT_7POINT0_FRONT       },
> +    { "7.1",            AV_CHANNEL_LAYOUT_7POINT1             },
> +    { "7.1(wide)",      AV_CHANNEL_LAYOUT_7POINT1_WIDE        },
> +    { "7.1(wide-back)", AV_CHANNEL_LAYOUT_7POINT1_WIDE_BACK   },
> +    { "octagonal",      AV_CHANNEL_LAYOUT_OCTAGONAL           },
> +    { "hexadecagonal",  AV_CHANNEL_LAYOUT_HEXADECAGONAL       },
> +    { "downmix",        AV_CHANNEL_LAYOUT_STEREO_DOWNMIX,     },
>  };
>  
> +#if FF_API_OLD_CHANNEL_LAYOUT
> +FF_DISABLE_DEPRECATION_WARNINGS
>  static uint64_t get_channel_layout_single(const char *name, int name_len)
>  {
>      int i;
> @@ -115,7 +127,7 @@ static uint64_t get_channel_layout_single(const char *name, int name_len)
>      for (i = 0; i < FF_ARRAY_ELEMS(channel_layout_map); i++) {
>          if (strlen(channel_layout_map[i].name) == name_len &&
>              !memcmp(channel_layout_map[i].name, name, name_len))
> -            return channel_layout_map[i].layout;
> +            return channel_layout_map[i].layout.u.mask;
>      }
>      for (i = 0; i < FF_ARRAY_ELEMS(channel_names); i++)
>          if (channel_names[i].name &&
> @@ -183,8 +195,8 @@ void av_bprint_channel_layout(struct AVBPrint *bp,
>          nb_channels = av_get_channel_layout_nb_channels(channel_layout);
>  
>      for (i = 0; i < FF_ARRAY_ELEMS(channel_layout_map); i++)
> -        if (nb_channels    == channel_layout_map[i].nb_channels &&
> -            channel_layout == channel_layout_map[i].layout) {
> +        if (nb_channels    == channel_layout_map[i].layout.nb_channels &&
> +            channel_layout == channel_layout_map[i].layout.u.mask) {
>              av_bprintf(bp, "%s", channel_layout_map[i].name);
>              return;
>          }
> @@ -195,7 +207,7 @@ void av_bprint_channel_layout(struct AVBPrint *bp,
>          av_bprintf(bp, " (");
>          for (i = 0, ch = 0; i < 64; i++) {
>              if ((channel_layout & (UINT64_C(1) << i))) {
> -                const char *name = get_channel_name(i);
> +                const char *name = av_channel_name(i);
>                  if (name) {
>                      if (ch > 0)
>                          av_bprintf(bp, "+");
> @@ -225,8 +237,8 @@ int av_get_channel_layout_nb_channels(uint64_t channel_layout)
>  int64_t av_get_default_channel_layout(int nb_channels) {
>      int i;
>      for (i = 0; i < FF_ARRAY_ELEMS(channel_layout_map); i++)
> -        if (nb_channels == channel_layout_map[i].nb_channels)
> -            return channel_layout_map[i].layout;
> +        if (nb_channels == channel_layout_map[i].layout.nb_channels)
> +            return channel_layout_map[i].layout.u.mask;
>      return 0;
>  }
>  
> @@ -247,7 +259,7 @@ const char *av_get_channel_name(uint64_t channel)
>          return NULL;
>      for (i = 0; i < 64; i++)
>          if ((1ULL<<i) & channel)
> -            return get_channel_name(i);
> +            return av_channel_name(i);
>      return NULL;
>  }
>  
> @@ -281,7 +293,252 @@ int av_get_standard_channel_layout(unsigned index, uint64_t *layout,
>  {
>      if (index >= FF_ARRAY_ELEMS(channel_layout_map))
>          return AVERROR_EOF;
> -    if (layout) *layout = channel_layout_map[index].layout;
> +    if (layout) *layout = channel_layout_map[index].layout.u.mask;
>      if (name)   *name   = channel_layout_map[index].name;
>      return 0;
>  }
> +
> +FF_ENABLE_DEPRECATION_WARNINGS
> +#endif
> +
> +void av_channel_layout_from_mask(AVChannelLayout *channel_layout,
> +                                 uint64_t mask)
> +{
> +    channel_layout->order       = AV_CHANNEL_ORDER_NATIVE;
> +    channel_layout->nb_channels = av_popcount64(mask);
> +    channel_layout->u.mask      = mask;
> +}
> +
> +int av_channel_layout_from_string(AVChannelLayout *channel_layout,
> +                                  const char *str)
> +{
> +    int i, channels;
> +    const char *dup = str;
> +    uint64_t mask = 0;
> +
> +    /* channel layout names */
> +    for (i = 0; i < FF_ARRAY_ELEMS(channel_layout_map); i++) {
> +        if (channel_layout_map[i].name && !strcmp(str, channel_layout_map[i].name)) {
> +            *channel_layout = channel_layout_map[i].layout;
> +            return 0;
> +        }
> +    }
> +
> +    /* channel names */
> +    while (*dup) {
> +        char *chname = av_get_token(&dup, "+");
> +        if (!chname)
> +            return AVERROR(ENOMEM);
> +        if (*dup)
> +            dup++; // skip separator
> +        for (i = 0; i < FF_ARRAY_ELEMS(channel_names); i++) {
> +            if (channel_names[i].name && !strcmp(chname, channel_names[i].name)) {
> +                mask |= 1ULL << i;
> +            }
> +        }
> +        av_free(chname);
> +    }
> +    if (mask) {
> +        av_channel_layout_from_mask(channel_layout, mask);
> +        return 0;
> +    }
> +
> +    /* channel layout mask */
> +    if (!strncmp(str, "0x", 2) && sscanf(str, "%"PRIx64, &mask) == 1) {
> +        av_channel_layout_from_mask(channel_layout, mask);
> +        return 0;
> +    }
> +
> +    /* number of channels */
> +    if (sscanf(str, "%d", &channels) == 1) {
> +        av_channel_layout_default(channel_layout, channels);
> +        return 0;
> +    }
> +
> +    /* number of unordered channels */
> +    if (sscanf(str, "%d channels", &channel_layout->nb_channels) == 1) {
> +        channel_layout->order = AV_CHANNEL_ORDER_UNSPEC;
> +        return 0;
> +    }
> +
> +    return AVERROR_INVALIDDATA;
> +}
> +
> +void av_channel_layout_uninit(AVChannelLayout *channel_layout)
> +{
> +    if (channel_layout->order == AV_CHANNEL_ORDER_CUSTOM)
> +        av_freep(&channel_layout->u.map);
> +    memset(channel_layout, 0, sizeof(*channel_layout));
> +}
> +
> +int av_channel_layout_copy(AVChannelLayout *dst, const AVChannelLayout *src)
> +{
> +    av_channel_layout_uninit(dst);
> +    *dst = *src;
> +    if (src->order == AV_CHANNEL_ORDER_CUSTOM) {
> +        dst->u.map = av_malloc(src->nb_channels * sizeof(*dst->u.map));
> +        if (!dst->u.map)
> +            return AVERROR(ENOMEM);
> +        memcpy(dst->u.map, src->u.map, src->nb_channels * sizeof(*src->u.map));
> +    }
> +    return 0;
> +}
> +
> +char *av_channel_layout_describe(const AVChannelLayout *channel_layout)
> +{
> +    int i;
> +
> +    switch (channel_layout->order) {
> +    case AV_CHANNEL_ORDER_NATIVE:
> +        for (i = 0; channel_layout_map[i].name; i++)
> +            if (channel_layout->u.mask == channel_layout_map[i].layout.u.mask)
> +                return av_strdup(channel_layout_map[i].name);
> +        // fall-through
> +    case AV_CHANNEL_ORDER_CUSTOM: {
> +        // max 4 bytes for channel name + a separator
> +        int size = 5 * channel_layout->nb_channels + 1;
> +        char *ret;
> +
> +        ret = av_mallocz(size);
> +        if (!ret)
> +            return NULL;
> +
> +        for (i = 0; i < channel_layout->nb_channels; i++) {
> +            enum AVChannel ch = av_channel_layout_get_channel(channel_layout, i);
> +            const char *ch_name = av_channel_name(ch);
> +
> +            if (i)
> +                av_strlcat(ret, "+", size);
> +            av_strlcat(ret, ch_name, size);
> +        }
> +        return ret;
> +        }
> +    case AV_CHANNEL_ORDER_UNSPEC: {
> +        char buf[64];
> +        snprintf(buf, sizeof(buf), "%d channels", channel_layout->nb_channels);
> +        return av_strdup(buf);
> +        }
> +    default:
> +        return NULL;
> +    }
> +}
> +
> +int av_channel_layout_get_channel(const AVChannelLayout *channel_layout, int idx)
> +{
> +    int i;
> +
> +    if (idx < 0 || idx >= channel_layout->nb_channels)
> +        return AVERROR(EINVAL);
> +
> +    switch (channel_layout->order) {
> +    case AV_CHANNEL_ORDER_CUSTOM:
> +        return channel_layout->u.map[idx];
> +    case AV_CHANNEL_ORDER_NATIVE:
> +        for (i = 0; i < 64; i++) {
> +            if ((1ULL << i) & channel_layout->u.mask && !idx--)
> +                return i;
> +        }
> +    default:
> +        return AVERROR(EINVAL);
> +    }
> +}
> +
> +int av_channel_layout_channel_index(const AVChannelLayout *channel_layout,
> +                                    enum AVChannel channel)
> +{
> +    int i;
> +
> +    switch (channel_layout->order) {
> +    case AV_CHANNEL_ORDER_CUSTOM:
> +        for (i = 0; i < channel_layout->nb_channels; i++)
> +            if (channel_layout->u.map[i] == channel)
> +                return i;
> +        return AVERROR(EINVAL);
> +    case AV_CHANNEL_ORDER_NATIVE: {
> +        uint64_t mask = channel_layout->u.mask;
> +        if (!(mask & (1ULL << channel)))
> +            return AVERROR(EINVAL);
> +        mask &= (1ULL << channel) - 1;
> +        return av_popcount64(mask);
> +        }
> +    default:
> +        return AVERROR(EINVAL);
> +    }
> +}
> +
> +int av_channel_layout_check(const AVChannelLayout *channel_layout)
> +{
> +    if (!channel_layout || channel_layout->nb_channels <= 0)
> +        return 0;
> +
> +    switch (channel_layout->order) {
> +    case AV_CHANNEL_ORDER_NATIVE:
> +        return av_popcount64(channel_layout->u.mask) == channel_layout->nb_channels;
> +    case AV_CHANNEL_ORDER_CUSTOM:
> +        return !!channel_layout->u.map;
> +    case AV_CHANNEL_ORDER_UNSPEC:
> +        return 1;
> +    default:
> +        return 0;
> +    }
> +}
> +
> +int av_channel_layout_compare(const AVChannelLayout *chl, const AVChannelLayout *chl1)
> +{
> +    /* different channel counts -> not equal */
> +    if (chl->nb_channels != chl1->nb_channels && chl->order == chl1->order)
> +        return (chl->nb_channels - chl1->nb_channels > 0) - (chl1->nb_channels - chl->nb_channels > 0);
> +
> +    /* if only one is unspecified -> not equal */
> +    if ((chl->order  == AV_CHANNEL_ORDER_UNSPEC) !=
> +        (chl1->order == AV_CHANNEL_ORDER_UNSPEC))
> +        return -2;
> +    /* both are unspecified -> equal */
> +    else if (chl->order == AV_CHANNEL_ORDER_UNSPEC)
> +        return 0;
> +
> +    /* can compare masks directly */
> +    if (chl->order != AV_CHANNEL_ORDER_CUSTOM &&
> +        chl->order == chl1->order)
> +        return chl->u.mask == chl1->u.mask ? 0 : -2;
> +
> +    /* compare channel by channel */
> +    for (int i = 0; i < chl->nb_channels; i++)
> +        if (av_channel_layout_get_channel(chl,  i) !=
> +            av_channel_layout_get_channel(chl1, i))
> +            return -2;
> +    return 0;
> +}
> +
> +void av_channel_layout_default(AVChannelLayout *ch_layout, int nb_channels)
> +{
> +    switch (nb_channels) {
> +    case 1: *ch_layout = (AVChannelLayout)AV_CHANNEL_LAYOUT_MONO;     break;
> +    case 2: *ch_layout = (AVChannelLayout)AV_CHANNEL_LAYOUT_STEREO;   break;
> +    case 3: *ch_layout = (AVChannelLayout)AV_CHANNEL_LAYOUT_SURROUND; break;
> +    case 4: *ch_layout = (AVChannelLayout)AV_CHANNEL_LAYOUT_QUAD;     break;
> +    case 5: *ch_layout = (AVChannelLayout)AV_CHANNEL_LAYOUT_5POINT0;  break;
> +    case 6: *ch_layout = (AVChannelLayout)AV_CHANNEL_LAYOUT_5POINT1;  break;
> +    case 7: *ch_layout = (AVChannelLayout)AV_CHANNEL_LAYOUT_6POINT1;  break;
> +    case 8: *ch_layout = (AVChannelLayout)AV_CHANNEL_LAYOUT_7POINT1;  break;
> +    default:
> +        ch_layout->order       = AV_CHANNEL_ORDER_UNSPEC;
> +        ch_layout->nb_channels = nb_channels;
> +    }
> +}
> +
> +uint64_t av_channel_layout_subset(const AVChannelLayout *channel_layout,
> +                                  uint64_t mask)
> +{
> +    uint64_t ret = 0;
> +    int i;
> +
> +    if (channel_layout->order == AV_CHANNEL_ORDER_NATIVE)
> +        return channel_layout->u.mask & mask;
> +
> +    for (i = 0; i < 64; i++)
> +        if (mask & (1ULL << i) && av_channel_layout_channel_index(channel_layout, i) >= 0)
> +            ret |= (1ULL << i);
> +
> +    return ret;
> +}
> diff --git a/libavutil/channel_layout.h b/libavutil/channel_layout.h
> index 50bb8f03c5..a4d76dc4f0 100644
> --- a/libavutil/channel_layout.h
> +++ b/libavutil/channel_layout.h
> @@ -24,6 +24,9 @@
>  
>  #include <stdint.h>
>  
> +#include "version.h"
> +#include "attributes.h"
> +
>  /**
>   * @file
>   * audio channel layout utility functions
> @@ -34,6 +37,60 @@
>   * @{
>   */
>  
> +enum AVChannel {
> +    AV_CHAN_FRONT_LEFT,
> +    AV_CHAN_FRONT_RIGHT,
> +    AV_CHAN_FRONT_CENTER,
> +    AV_CHAN_LOW_FREQUENCY,
> +    AV_CHAN_BACK_LEFT,
> +    AV_CHAN_BACK_RIGHT,
> +    AV_CHAN_FRONT_LEFT_OF_CENTER,
> +    AV_CHAN_FRONT_RIGHT_OF_CENTER,
> +    AV_CHAN_BACK_CENTER,
> +    AV_CHAN_SIDE_LEFT,
> +    AV_CHAN_SIDE_RIGHT,
> +    AV_CHAN_TOP_CENTER,
> +    AV_CHAN_TOP_FRONT_LEFT,
> +    AV_CHAN_TOP_FRONT_CENTER,
> +    AV_CHAN_TOP_FRONT_RIGHT,
> +    AV_CHAN_TOP_BACK_LEFT,
> +    AV_CHAN_TOP_BACK_CENTER,
> +    AV_CHAN_TOP_BACK_RIGHT,
> +    /** Stereo downmix. */
> +    AV_CHAN_STEREO_LEFT = 29,
> +    /** See above. */
> +    AV_CHAN_STEREO_RIGHT,
> +    AV_CHAN_WIDE_LEFT,
> +    AV_CHAN_WIDE_RIGHT,
> +    AV_CHAN_SURROUND_DIRECT_LEFT,
> +    AV_CHAN_SURROUND_DIRECT_RIGHT,
> +    AV_CHAN_LOW_FREQUENCY_2,
> +
> +    /** Channel is empty can be safely skipped. */
> +    AV_CHAN_SILENCE = 64,
> +};
> +
> +enum AVChannelOrder {
> +    /**
> +     * The native channel order, i.e. the channels are in the same order in
> +     * which they are defined in the AVChannel enum. This supports up to 63
> +     * different channels.
> +     */
> +    AV_CHANNEL_ORDER_NATIVE,
> +    /**
> +     * The channel order does not correspond to any other predefined order and
> +     * is stored as an explicit map. For example, this could be used to support

> +     * layouts with 64 or more channels, or with channels that could be skipped.

"or with channels that could be skipped"? What does that mean. If a
channel is skipped, it is not present, that can be expressed in the
mask. Is this a mistake for "duplicated"?

> +     */
> +    AV_CHANNEL_ORDER_CUSTOM,
> +    /**
> +     * Only the channel count is specified, without any further information
> +     * about the channel order.
> +     */
> +    AV_CHANNEL_ORDER_UNSPEC,
> +};
> +
> +
>  /**
>   * @defgroup channel_masks Audio channel masks
>   *
> @@ -46,36 +103,41 @@
>   *
>   * @{
>   */
> -#define AV_CH_FRONT_LEFT             0x00000001
> -#define AV_CH_FRONT_RIGHT            0x00000002
> -#define AV_CH_FRONT_CENTER           0x00000004
> -#define AV_CH_LOW_FREQUENCY          0x00000008
> -#define AV_CH_BACK_LEFT              0x00000010
> -#define AV_CH_BACK_RIGHT             0x00000020
> -#define AV_CH_FRONT_LEFT_OF_CENTER   0x00000040
> -#define AV_CH_FRONT_RIGHT_OF_CENTER  0x00000080
> -#define AV_CH_BACK_CENTER            0x00000100
> -#define AV_CH_SIDE_LEFT              0x00000200
> -#define AV_CH_SIDE_RIGHT             0x00000400
> -#define AV_CH_TOP_CENTER             0x00000800
> -#define AV_CH_TOP_FRONT_LEFT         0x00001000
> -#define AV_CH_TOP_FRONT_CENTER       0x00002000
> -#define AV_CH_TOP_FRONT_RIGHT        0x00004000
> -#define AV_CH_TOP_BACK_LEFT          0x00008000
> -#define AV_CH_TOP_BACK_CENTER        0x00010000
> -#define AV_CH_TOP_BACK_RIGHT         0x00020000
> -#define AV_CH_STEREO_LEFT            0x20000000  ///< Stereo downmix.
> -#define AV_CH_STEREO_RIGHT           0x40000000  ///< See AV_CH_STEREO_LEFT.
> -#define AV_CH_WIDE_LEFT              0x0000000080000000ULL
> -#define AV_CH_WIDE_RIGHT             0x0000000100000000ULL
> -#define AV_CH_SURROUND_DIRECT_LEFT   0x0000000200000000ULL
> -#define AV_CH_SURROUND_DIRECT_RIGHT  0x0000000400000000ULL
> -#define AV_CH_LOW_FREQUENCY_2        0x0000000800000000ULL
> +#define AV_CH_FRONT_LEFT             (1ULL << AV_CHAN_FRONT_LEFT           )
> +#define AV_CH_FRONT_RIGHT            (1ULL << AV_CHAN_FRONT_RIGHT          )
> +#define AV_CH_FRONT_CENTER           (1ULL << AV_CHAN_FRONT_CENTER         )
> +#define AV_CH_LOW_FREQUENCY          (1ULL << AV_CHAN_LOW_FREQUENCY        )
> +#define AV_CH_BACK_LEFT              (1ULL << AV_CHAN_BACK_LEFT            )
> +#define AV_CH_BACK_RIGHT             (1ULL << AV_CHAN_BACK_RIGHT           )
> +#define AV_CH_FRONT_LEFT_OF_CENTER   (1ULL << AV_CHAN_FRONT_LEFT_OF_CENTER )
> +#define AV_CH_FRONT_RIGHT_OF_CENTER  (1ULL << AV_CHAN_FRONT_RIGHT_OF_CENTER)
> +#define AV_CH_BACK_CENTER            (1ULL << AV_CHAN_BACK_CENTER          )
> +#define AV_CH_SIDE_LEFT              (1ULL << AV_CHAN_SIDE_LEFT            )
> +#define AV_CH_SIDE_RIGHT             (1ULL << AV_CHAN_SIDE_RIGHT           )
> +#define AV_CH_TOP_CENTER             (1ULL << AV_CHAN_TOP_CENTER           )
> +#define AV_CH_TOP_FRONT_LEFT         (1ULL << AV_CHAN_TOP_FRONT_LEFT       )
> +#define AV_CH_TOP_FRONT_CENTER       (1ULL << AV_CHAN_TOP_FRONT_CENTER     )
> +#define AV_CH_TOP_FRONT_RIGHT        (1ULL << AV_CHAN_TOP_FRONT_RIGHT      )
> +#define AV_CH_TOP_BACK_LEFT          (1ULL << AV_CHAN_TOP_BACK_LEFT        )
> +#define AV_CH_TOP_BACK_CENTER        (1ULL << AV_CHAN_TOP_BACK_CENTER      )
> +#define AV_CH_TOP_BACK_RIGHT         (1ULL << AV_CHAN_TOP_BACK_RIGHT       )
> +#define AV_CH_STEREO_LEFT            (1ULL << AV_CHAN_STEREO_LEFT          )
> +#define AV_CH_STEREO_RIGHT           (1ULL << AV_CHAN_STEREO_RIGHT         )
> +#define AV_CH_WIDE_LEFT              (1ULL << AV_CHAN_WIDE_LEFT            )
> +#define AV_CH_WIDE_RIGHT             (1ULL << AV_CHAN_WIDE_RIGHT           )
> +#define AV_CH_SURROUND_DIRECT_LEFT   (1ULL << AV_CHAN_SURROUND_DIRECT_LEFT )
> +#define AV_CH_SURROUND_DIRECT_RIGHT  (1ULL << AV_CHAN_SURROUND_DIRECT_RIGHT)
> +#define AV_CH_LOW_FREQUENCY_2        (1ULL << AV_CHAN_LOW_FREQUENCY_2      )
>  
> +#if FF_API_OLD_CHANNEL_LAYOUT
>  /** Channel mask value used for AVCodecContext.request_channel_layout
>      to indicate that the user requests the channel order of the decoder output
> -    to be the native codec channel order. */
> +    to be the native codec channel order.
> +    @deprecated channel order is now indicated in a special field in
> +                AVChannelLayout
> +    */
>  #define AV_CH_LAYOUT_NATIVE          0x8000000000000000ULL
> +#endif
>  
>  /**
>   * @}
> @@ -122,6 +184,135 @@ enum AVMatrixEncoding {
>      AV_MATRIX_ENCODING_NB
>  };
>  
> +/**
> + * An AVChannelLayout holds information about the channel layout of audio data.
> + *
> + * A channel layout here is defined as a set of channels ordered in a specific
> + * way (unless the channel order is AV_CHANNEL_ORDER_UNSPEC, in which case an
> + * AVChannelLayout carries only the channel count).
> + *

> + * Unlike most structures in Libav, sizeof(AVChannelLayout) is a part of the
> + * public ABI and may be used by the caller. E.g. it may be allocated on stack.
> + * In particular, this structure can be initialized as follows:
> + * - default initialization with {0} or by setting all used fields correctly
> + * - with predefined layout as initializer (AV_CHANNEL_LAYOUT_STEREO, etc.)
> + * - with a constructor function such as av_channel_layout_default()
> + * On that note, this also applies:
> + * - copy via assigning is forbidden, av_channel_layout_copy() must be used
> + *   instead (and its return value should be checked)
> + * - if order is AV_CHANNEL_ORDER_CUSTOM, then it must be uninitialized with
> + *   av_channel_layout_uninit().
> + *
> + * No new fields may be added to it without a major version bump, except for
> + * new elements of the union fitting in sizeof(uint64_t).

This is a significant difference from the other APIs, and we need to be
really sure we can live with it.

I am rather for this version, but I am afraid we will find cases that
need extending the structure. After all, the trial by fire for an API is
to be used, this one has not yet had it.

I suggest we explicitly declare this API unstable for a few months,
during which we consider acceptable to add fields.

> + *
> + * An AVChannelLayout can be constructed using the convenience function
> + * av_channel_layout_from_mask() / av_channel_layout_from_string(), or it can be
> + * built manually by the caller.
> + */
> +typedef struct AVChannelLayout {
> +    /**
> +     * Channel order used in this layout.
> +     * This is a mandatory field, will default to AV_CHANNEL_ORDER_NATIVE.
> +     */
> +    enum AVChannelOrder order;
> +
> +    /**
> +     * Number of channels in this layout. Mandatory field.
> +     */

> +    int nb_channels;

unsigned.

> +
> +    /**
> +     * Details about which channels are present in this layout.
> +     * For AV_CHANNEL_ORDER_UNSPEC, this field is undefined and must not be
> +     * used.
> +     */
> +    union {
> +        /**
> +         * This member must be used for AV_CHANNEL_ORDER_NATIVE.
> +         * It is a bitmask, where the position of each set bit means that the
> +         * AVChannel with the corresponding value is present.
> +         *
> +         * I.e. when (mask & (1 << AV_CHAN_FOO)) is non-zero, then AV_CHAN_FOO
> +         * is present in the layout. Otherwise it is not present.
> +         *
> +         * @note when a channel layout using a bitmask is constructed or
> +         * modified manually (i.e.  not using any of the av_channel_layout_*
> +         * functions), the code doing it must ensure that the number of set bits
> +         * is equal to nb_channels.
> +         */
> +        uint64_t mask;
> +        /**
> +         * This member must be used when the channel order is
> +         * AV_CHANNEL_ORDER_CUSTOM. It is a nb_channels-sized array, with each
> +         * element signalling the presend of the AVChannel with the
> +         * corresponding value.
> +         *
> +         * I.e. when map[i] is equal to AV_CHAN_FOO, then AV_CH_FOO is the i-th
> +         * channel in the audio data.
> +         */
> +        enum AVChannel *map;
> +    } u;
> +} AVChannelLayout;
> +

> +#define AV_CHANNEL_LAYOUT_MONO \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 1,  .u = { .mask = AV_CH_LAYOUT_MONO }}

These macros can only be used to init structures. This is unusual for
macros in ALL_CAPS, and therefore it needs to be documented.

> +#define AV_CHANNEL_LAYOUT_STEREO \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 2,  .u = { .mask = AV_CH_LAYOUT_STEREO }}
> +#define AV_CHANNEL_LAYOUT_2POINT1 \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 3,  .u = { .mask = AV_CH_LAYOUT_2POINT1 }}
> +#define AV_CHANNEL_LAYOUT_2_1 \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 3,  .u = { .mask = AV_CH_LAYOUT_2_1 }}
> +#define AV_CHANNEL_LAYOUT_SURROUND \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 3,  .u = { .mask = AV_CH_LAYOUT_SURROUND }}
> +#define AV_CHANNEL_LAYOUT_3POINT1 \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 4,  .u = { .mask = AV_CH_LAYOUT_3POINT1 }}
> +#define AV_CHANNEL_LAYOUT_4POINT0 \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 4,  .u = { .mask = AV_CH_LAYOUT_4POINT0 }}
> +#define AV_CHANNEL_LAYOUT_4POINT1 \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 5,  .u = { .mask = AV_CH_LAYOUT_4POINT1 }}
> +#define AV_CHANNEL_LAYOUT_2_2 \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 4,  .u = { .mask = AV_CH_LAYOUT_2_2 }}
> +#define AV_CHANNEL_LAYOUT_QUAD \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 4,  .u = { .mask = AV_CH_LAYOUT_QUAD }}
> +#define AV_CHANNEL_LAYOUT_5POINT0 \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 5,  .u = { .mask = AV_CH_LAYOUT_5POINT0 }}
> +#define AV_CHANNEL_LAYOUT_5POINT1 \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 6,  .u = { .mask = AV_CH_LAYOUT_5POINT1 }}
> +#define AV_CHANNEL_LAYOUT_5POINT0_BACK \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 5,  .u = { .mask = AV_CH_LAYOUT_5POINT0_BACK }}
> +#define AV_CHANNEL_LAYOUT_5POINT1_BACK \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 6,  .u = { .mask = AV_CH_LAYOUT_5POINT1_BACK }}
> +#define AV_CHANNEL_LAYOUT_6POINT0 \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 6,  .u = { .mask = AV_CH_LAYOUT_6POINT0 }}
> +#define AV_CHANNEL_LAYOUT_6POINT0_FRONT \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 6,  .u = { .mask = AV_CH_LAYOUT_6POINT0_FRONT }}
> +#define AV_CHANNEL_LAYOUT_HEXAGONAL \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 6,  .u = { .mask = AV_CH_LAYOUT_HEXAGONAL }}
> +#define AV_CHANNEL_LAYOUT_6POINT1 \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 7,  .u = { .mask = AV_CH_LAYOUT_6POINT1 }}
> +#define AV_CHANNEL_LAYOUT_6POINT1_BACK \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 7,  .u = { .mask = AV_CH_LAYOUT_6POINT1_BACK }}
> +#define AV_CHANNEL_LAYOUT_6POINT1_FRONT \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 7,  .u = { .mask = AV_CH_LAYOUT_6POINT1_FRONT }}
> +#define AV_CHANNEL_LAYOUT_7POINT0 \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 7,  .u = { .mask = AV_CH_LAYOUT_7POINT0 }}
> +#define AV_CHANNEL_LAYOUT_7POINT0_FRONT \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 7,  .u = { .mask = AV_CH_LAYOUT_7POINT0_FRONT }}
> +#define AV_CHANNEL_LAYOUT_7POINT1 \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 8,  .u = { .mask = AV_CH_LAYOUT_7POINT1 }}
> +#define AV_CHANNEL_LAYOUT_7POINT1_WIDE \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 8,  .u = { .mask = AV_CH_LAYOUT_7POINT1_WIDE }}
> +#define AV_CHANNEL_LAYOUT_7POINT1_WIDE_BACK \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 8,  .u = { .mask = AV_CH_LAYOUT_7POINT1_WIDE_BACK }}
> +#define AV_CHANNEL_LAYOUT_OCTAGONAL \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 8,  .u = { .mask = AV_CH_LAYOUT_OCTAGONAL }}
> +#define AV_CHANNEL_LAYOUT_HEXADECAGONAL \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 16, .u = { .mask = AV_CH_LAYOUT_HEXAGONAL }}
> +#define AV_CHANNEL_LAYOUT_STEREO_DOWNMIX \
> +    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 2,  .u = { .mask = AV_CH_LAYOUT_STEREO_DOWNMIX }}
> +
> +#if FF_API_OLD_CHANNEL_LAYOUT
>  /**
>   * Return a channel layout id that matches name, or 0 if no match is found.
>   *
> @@ -138,7 +329,10 @@ enum AVMatrixEncoding {
>   *   AV_CH_* macros).
>   *
>   * Example: "stereo+FC" = "2c+FC" = "2c+1c" = "0x7"
> + *
> + * @deprecated use av_channel_layout_from_string()
>   */
> +attribute_deprecated
>  uint64_t av_get_channel_layout(const char *name);
>  
>  /**
> @@ -161,7 +355,9 @@ int av_get_extended_channel_layout(const char *name, uint64_t* channel_layout, i
>   *
>   * @param buf put here the string containing the channel layout
>   * @param buf_size size in bytes of the buffer
> + * @deprecated use av_channel_layout_describe()
>   */
> +attribute_deprecated
>  void av_get_channel_layout_string(char *buf, int buf_size, int nb_channels, uint64_t channel_layout);
>  
>  struct AVBPrint;
> @@ -172,12 +368,17 @@ void av_bprint_channel_layout(struct AVBPrint *bp, int nb_channels, uint64_t cha
>  
>  /**
>   * Return the number of channels in the channel layout.
> + * @deprecated use AVChannelLayout.nb_channels
>   */
> +attribute_deprecated
>  int av_get_channel_layout_nb_channels(uint64_t channel_layout);
>  
>  /**
>   * Return default channel layout for a given number of channels.
> + *
> + * @deprecated use av_channel_layout_default()
>   */
> +attribute_deprecated
>  int64_t av_get_default_channel_layout(int nb_channels);
>  
>  /**
> @@ -188,20 +389,28 @@ int64_t av_get_default_channel_layout(int nb_channels);
>   *
>   * @return index of channel in channel_layout on success, a negative AVERROR
>   *         on error.
> + *
> + * @deprecated use av_channel_layout_channel_index()
>   */
> +attribute_deprecated
>  int av_get_channel_layout_channel_index(uint64_t channel_layout,
>                                          uint64_t channel);
>  
>  /**
>   * Get the channel with the given index in channel_layout.
> + * @deprecated use av_channel_layout_get_channel()
>   */
> +attribute_deprecated
>  uint64_t av_channel_layout_extract_channel(uint64_t channel_layout, int index);
>  
>  /**
>   * Get the name of a given channel.
>   *
>   * @return channel name on success, NULL on error.
> + *
> + * @deprecated use av_channel_name()
>   */
> +attribute_deprecated
>  const char *av_get_channel_name(uint64_t channel);
>  
>  /**
> @@ -210,6 +419,7 @@ const char *av_get_channel_name(uint64_t channel);
>   * @param channel  a channel layout with a single channel
>   * @return  channel description on success, NULL on error
>   */
> +attribute_deprecated
>  const char *av_get_channel_description(uint64_t channel);
>  
>  /**
> @@ -221,9 +431,158 @@ const char *av_get_channel_description(uint64_t channel);
>   * @return  0  if the layout exists,
>   *          <0 if index is beyond the limits
>   */
> +attribute_deprecated
>  int av_get_standard_channel_layout(unsigned index, uint64_t *layout,
>                                     const char **name);
>  
> +#endif
> +
> +/**
> + * This is the inverse function of @ref av_channel_from_string().
> + *
> + * @return a string describing a given channel, or NULL if not found.
> + */
> +const char *av_channel_name(enum AVChannel channel);
> +
> +/**
> + * This is the inverse function of @ref av_channel_name().
> + *
> + * @return a channel described by the given string, or a negative AVERROR value.
> + */
> +int av_channel_from_string(const char *name);
> +
> +/**
> + * Initialize a native channel layout from a bitmask indicating which channels
> + * are present.
> + *
> + * @note channel_layout should be properly allocated as described above.
> + *
> + * @param channel_layout the layout structure to be initialized
> + * @param mask bitmask describing the channel layout
> + */
> +void av_channel_layout_from_mask(AVChannelLayout *channel_layout, uint64_t mask);
> +
> +/**
> + * Initialize a channel layout from a given string description.
> + * The input string can be represented by:
> + *  - the formal channel layout name (returned by av_channel_layout_describe())
> + *  - single or multiple channel names (returned by av_channel_name()
> + *    or concatenated with "+")
> + *  - a hexadecimal value of a channel layout (eg. "0x4")
> + *  - the number of channels with default layout (eg. "5")
> + *  - the number of unordered channels (eg. "4 channels")
> + *
> + * @note channel_layout should be properly allocated as described above.
> + *
> + * @param channel_layout input channel layout
> + * @param str string describing the channel layout
> + * @return 0 channel layout was detected, AVERROR_INVALIDATATA otherwise
> + */
> +int av_channel_layout_from_string(AVChannelLayout *channel_layout,
> +                                  const char *str);
> +
> +/**
> + * Get the default channel layout for a given number of channels.
> + *
> + * @note channel_layout should be properly allocated as described above.
> + *
> + * @param channel_layout the layout structure to be initialized
> + * @param nb_channels number of channels
> + */

> +void av_channel_layout_default(AVChannelLayout *ch_layout, int nb_channels);

unsigned nb_channels

> +
> +/**
> + * Free any allocated data in the channel layout and reset the channel
> + * count to 0.
> + *
> + * @note this only used for structure initialization and for freeing the
> + *       allocated memory for AV_CHANNEL_ORDER_CUSTOM order.
> + *
> + * @param channel_layout the layout structure to be uninitialized
> + */
> +void av_channel_layout_uninit(AVChannelLayout *channel_layout);
> +
> +/**
> + * Make a copy of a channel layout. This differs from just assigning src to dst
> + * in that it allocates and copies the map for AV_CHANNEL_ORDER_CUSTOM.
> + *
> + * @note the destination channel_layout will be always uninitialized before copy.
> + *
> + * @param dst destination channel layout
> + * @param src source channel layout
> + * @return 0 on success, a negative AVERROR on error.
> + */
> +int av_channel_layout_copy(AVChannelLayout *dst, const AVChannelLayout *src);
> +

> +/**
> + * Get a human-readable string describing the channel layout properties.
> + *
> + * @note The returned string is allocated with av_malloc(),
> + *       and must be freed by the caller with av_free().

The relation between av_channel_layout_copy() and
av_channel_layout_from_string() needs to be documented.

> + *
> + * @param channel_layout channel layout to be described
> + * @return a string describing the structure or NULL on failure in the same
> + *         format that is accepted by @ref av_channel_layout_from_string().
> + */
> +char *av_channel_layout_describe(const AVChannelLayout *channel_layout);
> +
> +/**
> + * Get the channel with the given index in a channel layout.
> + *
> + * @param channel_layout input channel layout
> + * @return channel with the index idx in channel_layout on success or a negative
> + *                 AVERROR on failure (if idx is not valid or the channel order
> + *                 is unspecified)
> + */

> +int av_channel_layout_get_channel(const AVChannelLayout *channel_layout, int idx);

unsigned idx

But do we really need this as part of the API?

> +
> +/**
> + * Get the index of a given channel in a channel layout. In case multiple
> + * channels are found, only the first match will be returned.
> + *
> + * @param channel_layout input channel layout
> + * @return index of channel in channel_layout on success or a negative number if
> + *         channel is not present in channel_layout.
> + */

> +int av_channel_layout_channel_index(const AVChannelLayout *channel_layout,
> +                                    enum AVChannel channel);

Same: do we reall yneed this?

> +
> +/**
> + * Find out what channels from a given set are present in a channel layout,
> + * without regard for their positions.
> + *
> + * @param channel_layout input channel layout
> + * @param mask a combination of AV_CH_* representing a set of channels
> + * @return a bitfield representing all the channels from mask that are present
> + *         in channel_layout
> + */
> +uint64_t av_channel_layout_subset(const AVChannelLayout *channel_layout,
> +                                  uint64_t mask);

Same.

> +
> +/**
> + * Check whether a channel layout is valid, i.e. can possibly describe audio
> + * data.
> + *
> + * @param channel_layout input channel layout
> + * @return 1 if channel_layout is valid, 0 otherwise.
> + */
> +int av_channel_layout_check(const AVChannelLayout *channel_layout);
> +
> +/**
> + * Check whether two channel layouts are semantically the same, i.e. the same
> + * channels are present on the same positions in both.
> + *
> + * If one of the channel layouts is AV_CHANNEL_ORDER_UNSPEC, while the other is
> + * not, they are considered to be unequal. If both are AV_CHANNEL_ORDER_UNSPEC,
> + * they are considered equal iff the channel counts are the same in both.
> + *
> + * @param chl input channel layout
> + * @param chl1 input channel layout
> + * @return 0 if chl and chl1 are equal, 1 or -1 if they are not equal but are
> + *         same order. -2 code if they do not match some other way.
> + */
> +int av_channel_layout_compare(const AVChannelLayout *chl, const AVChannelLayout *chl1);
> +
>  /**
>   * @}
>   * @}
> diff --git a/libavutil/version.h b/libavutil/version.h
> index 27d663baf1..5e025c463f 100644
> --- a/libavutil/version.h
> +++ b/libavutil/version.h
> @@ -129,6 +129,9 @@
>  #ifndef FF_API_PSEUDOPAL
>  #define FF_API_PSEUDOPAL                (LIBAVUTIL_VERSION_MAJOR < 57)
>  #endif
> +#ifndef FF_API_OLD_CHANNEL_LAYOUT
> +#define FF_API_OLD_CHANNEL_LAYOUT       (LIBAVUTIL_VERSION_MAJOR < 58)
> +#endif
>  
>  
>  /**

Regards,

-- 
  Nicolas George
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