[FFmpeg-devel] [PATCH] aacdec: add support for dual mono in Japanese DTV

[Michael Niedermayer]

On Fri, Aug 24, 2012 at 09:45:37PM +0900, Akihiro TSUKADA wrote:
> (2012年08月24日 11:26), Michael Niedermayer wrote:
> >>> so there is no way to distinguish dual mono from stereo and the user
> >>> has to set this for each program she wants to watch manually ?
> >>
> >> There is, at the level of MPEG TS system.
> >>> so there is no way to distinguish dual mono from stereo and the user
> >>> has to set this for each program she wants to watch manually ?
> >>
> >> There is, at the level of MPEG TS system.
> >> Each audio PES is tagged by PMT and
> >> EIT describes the mapping from tag to encoding parameters
> >> including channel configuration.
> >> So those parameters are defined per program/show and
> >> can change over time. (PMT is usually fixed and does not change).
> >> TV receivers track EIT of the current station (TS, programID) and
> >> output either channel (defaulting to the left) or
> >> switch among them on user's request.
> >
> > Is this information available to the TS demuxer ? If so it could
> > maybe be passed to the decoder via side data on AVPackets, this would
> > avoid the need to manually set it
> 
> TS demuxer cannot know at packet accurate level when a program/show
> starts or ends, nor at which AAC frame dual mono starts or ends.
> Thus, decoder is expected to detect dual mono and not do decode
> both channels without the (inaccurate) designation from demuxer.

ok, but could the ts demuxer transmit enough information to
the aac decoder so the aac decoder could then find out where exactly
dual mono ends and starts?
I am thinking of a "is Japanese DTV" flag in side data or extra data
(extra data must not change throughout the stream though)
with which the decoder can then detect dual mono together with
dual SCE chan config=0


> 
> It may be possible that demuxer can automatically select
> which dual mono channel to decode, for example, based on the user's
> language preference, but still it is required that users can change
> the selected channel when they want it.
> Every Japanese TV has a "switch audio" button,
> and people occasionally choose to change  audio to English version.

yes, i agree there should be a way to override

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Into a blind darkness they enter who follow after the Ignorance,
they as if into a greater darkness enter who devote themselves
to the Knowledge alone. -- Isha Upanishad
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 198 bytes
Desc: Digital signature
URL: <http://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20120824/8b75aaaf/attachment.asc>