[FFmpeg-trac] #929(avcodec:new): AAC 5.1 channel decoding issue
FFmpeg
trac at avcodec.org
Wed Jan 25 13:04:06 CET 2012
#929: AAC 5.1 channel decoding issue
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Reporter: kaijun61 | Owner:
Type: defect | Status: new
Priority: normal | Component: avcodec
Version: git-master | Resolution:
Keywords: AAC | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
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Comment (by kaijun61):
Replying to [comment:11 cehoyos]:
> Replying to [comment:10 kaijun61]:
> > I assume ffmpeg application decodes aac, then downmixes it. If I just
use aac codec as a plugin. it can't do downmixing. As you said, I need
down-mixing routines to implement it externally.
>
> Don't you think that down-mixing will be generally needed, i.e. users
might want a particular down-mixing that is not supported by any codec,
how should this work without your application supporting FFmpeg's down-
mixing routines?
I think most of hand devices support stereo output only. If users play a
5-channel movie, they would feel poor quality sound.
> > Any particular reason not to implement it internally unlike other
codecs?
> Yes, many:
> * This work has to be duplicated for every codec that supports
multichannel encoding (and I suspect that for some lossless codecs, this
will be difficult) and development time unfortunately is a limiting
factor.
> * The general down-mixing code can easily be optimized for different
CPUs, optimizing it codec-wise is significantly more difficult.
> * Assuming the down-mixing does not come for free, it means a
performance penalty for users who do not want down-mixing.
>
> I suspect that all three points may not be relevant for AAC, but I do
not know, otoh, I cannot believe that AAC - and TrueHD, AC-3 and DTS - are
the only codecs for which GStreamer-users expect down-mixing. (Does
GStreamer really not support down-mixing?)
I need to investigate if GStreamer has downmixing plugin.
--
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/929#comment:12>
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