On 12/26/18, Nicolas George <geo...@nsup.org> wrote:
> Paul B Mahol (2018-12-24):
>> 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 <an...@khirnov.net>.
>> Expanded and completed by Vittorio Giovara <vittorio.giov...@gmail.com>.
>
>> Adopted for FFmpeg by Paul B Mahol <one...@gmail.com>.
>
> Adapted?
>
> Reviewing only the visible API for now.
>
>> diff --git a/libavutil/channel_layout.h b/libavutil/channel_layout.h
>> index 50bb8f03c5..e6c8c58b9c 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.
>> + */
>> + 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).
>> + *
>> + * 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;
>
> This should be 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 }}
>
> Does this mean that named fields is no longer an issue with any of the
> supported compilers?
>
>> +#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 }}
>> +
>
> <snip deprecating stuff>
>
>> +
>> +/**
>> + * This is the inverse function of @ref av_channel_from_string().
>> + *
>
>> + * @return a string describing a given channel, "?" if not found.
>
> AFAIR, none of our other get_name()-style API return "?" if not found,
> they all return NULL and let the application set a substitution string.
> Let us make this API consistent.
>
>> + */
>> +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);
>
> If it is really the exact inverse of av_channel_name(), then it should
> be av_channel_from_name(). If it accepts other syntaxes too, then they
> should be documented.
>
>> +
>> +/**
>> + * 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")
>
> av_get_channel_layout() used to use '+' instead of '|', and I think it
> is better. For once, '+' is not a special character for shells.
Look folk, I'm not paid to do this nor I'm paid to read your "reviews"
so I will ignore this one.
>
>> + *
>> + * @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 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().
>> + *
>> + * @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);
>
> There should also be av_channel_layout_describe_to_bprint() to let the
> user control the buffer allocation with more ease.
>
>> +
>> +/**
>> + * 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);
>> +
>> +/**
>> + * 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);
>> +
>> +/**
>> + * 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);
>> +
>> +/**
>> + * 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 if they are not equal. A
>> negative
>> + * AVERROR code if one or both are invalid.
>> + */
>> +int av_channel_layout_compare(const AVChannelLayout *chl, const
>> AVChannelLayout *chl1);
>> +
>> /**
>> * @}
>> * @}
>
> No more remarks for the first round of review.
>
> Regards,
>
> --
> Nicolas George
>
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