LPCM in mpeg(ts)

[Michael Olbrich]

On Wed, Apr 27, 2016 at 09:12:22AM +0300, Sebastian Dröge wrote:
> On Di, 2016-04-26 at 12:42 +0200, Michael Olbrich wrote:
> > Hi,
> > 
> > I have a mpegts stream with LPCM audio that is currently not supported by
> > the tsdemux element. I'm looking for some advice on the best way to
> > implement this. The specification can be found here[1].
> > It's similar to the format implemented in dvdlpcmdec. Just a different
> > header. The stream type is 0x83.
> 
> What are all the differences between this and the already supported
> LPCM?

Just the header: Different size and some fields are different.

> > I hacked dvdlpcmdec to support a different header. That works sometimes,
> > but the event handling in dvdlpcmdec is rather broken and the pipeline
> > fails to start occasionally.
> > 
> > I looked into rewriting dvdlpcmdec to use GstAudioDecoder but that's where
> > I got stuck:
> > The format currently supported by dvdlpcmdec is somewhat special: The
> > buffer timestamp might not refer to the first sample but somewhere in the
> > middle (the offset is specified in the header). I have no idea how to
> > handle this with GstAudioDecoder.
> 
> Take a look at e.g. a52dec, it is solving exactly the same problem
> for audio/x-private1-ac3 caps coming from DVDs.
> 
> > Any Ideas? Maybe split it into a parser and decoder and handle the header
> > and timestamps in the parser?
> > 
> > And what caps should tsdemux produce for the new format?
> > audio/x-private2-lpcm?
> 
> Seems like a good start, yes.

Thanks for the tips. I've created a new bug[1] with the initial version of
my patches.

Regards,
Michael

[1] https://bugzilla.gnome.org/show_bug.cgi?id=765807

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