[FFmpeg-devel] Channel layouts for aac encoding/decoding and vorbis decoding

Robert Swain robert.swain
Tue Aug 11 15:43:58 CEST 2009

2009/8/10 Jason Tackaberry <tack at urandom.ca>:
> On Mon, 2009-08-10 at 11:32 -0700, Frank Barchard wrote:
>> The actual layout we settle on is not that important - its just important
>> that we pick one.
>> It could also be different per platform, if really necessary, so long as
>> there are macros to specify the channel order.
>> By far the emphasis is 5.1, but if we could make all the other layouts
>> consistent and easy, that would be nice.
> I'm under the impression a good deal of work had already gone into this
> task last year (the "Channel layouts" thread started August 2008, which
> I mentioned in my initial email).
> The channel order is at least clearly defined by the CH_* values in
> avcodec.h (whose bits from LSB to MSB specify the order, which
> corresponds to the Wave order). ?So at this point it's a matter of
> gradually migrating the remaining codecs to the new standard channel
> layout.

Indeed. It just hasn't been implemented in AAC and Vorbis yet. I'm
looking at AAC and I may do the same for Vorbis while I'm at it.

> Hopefully at least the AAC and Vorbis decoder maintainers can give me
> some idea of how likely the current order is to change over the medium
> term. ?(I've already heard from Alex on the AAC encoder and adapting the
> channel layout is not on his radar.)

I should get the channel order stuff fixed in AAC shortly when we've
decided what the orders from the AAC spec are supposed to mean in
terms of the WAVEFORMATEXTENSIBLE layouts. And then I may do the same
for Vorbis as well. Its layouts are quite simple.


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