On Fri, 5 May 2017 22:20:18 -0400
Vittorio Giovara <[email protected]> wrote:
> +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.
> + */
> + AV_CHANNEL_ORDER_CUSTOM,
> + /**
> + * Only the channel count is specified, without any further information
> + * about the channels.
> + */
> + AV_CHANNEL_ORDER_UNSPEC,
> +};
> +typedef struct AVChannelLayout {
> + /**
> + * Channel order used in this layout.
> + */
> + enum AVChannelOrder order;
> +
> + /**
> + * Number of channels in this layout. Mandatory field.
> + */
> + int nb_channels;
> +
> + /**
> + * 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 not native, and
> + * represents a nb_channels-sized array. Its semantics may depending
> on
> + * the channel order.
> + *
> + * - For AV_CHANNEL_ORDER_CUSTOM: each element signals the presence
> of
> + * the AVChannel with the corresponding value: eg. when map[i] is
> + * equal to AV_CHAN_FOO, then AV_CHAN_FOO is the i-th channel in
> + * the audio data.
Does it allow a channel to be mapped more than once? Does it allow
padding channels (that would be all-0)?
> + */
> + uint8_t *map;
> + } u;
> +} AVChannelLayout;
So AV_CHANNEL_ORDER_CUSTOM is as powerful as AV_CHANNEL_ORDER_NATIVE,
just that it allows an arbitrary order?
How would layouts that don't fit into the channel label schema be
handled?
How would that ambisonic stuff be represented?
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