On 5/6/17 5:13 AM, wm4 wrote:
> On Fri, 5 May 2017 22:20:18 -0400
> Vittorio Giovara <vittorio.giov...@gmail.com> 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?
As a different AV_CHANNEL_ORDER
_______________________________________________
libav-devel mailing list
libav-devel@libav.org
https://lists.libav.org/mailman/listinfo/libav-devel
