[FFmpeg-devel] [PATCH] DVB LATM parser

[Michael Niedermayer]

On Thu, Feb 12, 2009 at 07:02:56PM +1300, Paul Kendall wrote:
> On Thursday 12 February 2009 00:53:21 Jai Menon wrote:
> > On Sun, Feb 1, 2009 at 4:37 AM, Paul Kendall <paul at kcbbs.gen.nz> wrote:
> > > Micheal,
> > > Sorry for the long delay in this! Been really busy with other things.
> > > Now there is a bit of noise on the MythTV lists about this so I thought
> > > it time that I get back to it.
> > >
> > > On Thursday 18 September 2008 06:24:48 Michael Niedermayer wrote:
> > >> Hi
> > >>
> > >> On Wed, Sep 17, 2008 at 04:57:46PM +1200, Paul Kendall wrote:
> > >> > On Wednesday 17 September 2008 12:51:18 Michael Niedermayer wrote:
> > >> > > On Fri, Jul 04, 2008 at 09:28:37AM +1200, Paul Kendall wrote:
> > >> > > > On Thursday 03 July 2008 22:16:56 Paul Kendall wrote:
> > >> > > > > Hi attached is a patch that provides a AAC LATM parser
> > >> > > > > CODEC_ID_AAC_LATM I have been working on. The libfaad decoder is
> > >> > > > > also patched to provide another codec the decoding for this
> > >> > > > > codec id. There are minor patches to mpeg.c & mpegts.c to send
> > >> > > > > stream id 0x11 to this codec id.
> > >> > > > >
> > >> > > > > With this patch I can get audio working perfectly for NZ DVB-T
> > >> > > > > using the stock unpatched libfaad2 library.
> > >> > > > >
> > >> > > > > I would welcome comments and suggestions so this can be included
> > >> > > > > in the ffmpeg codebase.
> > >> > > > >
> > >> > > > > Cheers,
> > >> > > > > Paul Kendall
> > >> > > >
> > >> > > > Doh!
> > >> > > > I missed a vital part of the patch! Putting the codec in the
> > >> > > > allcodecs.c file! Heres a modified patch.
> > >> > >
> > >> > > I think a parser is not the correct place to remove the LATM stuff.
> > >> > > A parser should only split things into frames and extract
> > >> > > information, not remove information.
> > >> > > This for example is important if one wants to preserve the LATM and
> > >> > > mux it into another container.
> > >> > > LATM could be removed in a bitstream filter ....
> > >> >
> > >> > Ok, I can look into this. Is there any docs on this.
> > >>
> > >> well ... the source code :)
> > >> but you can ask questions here if you have any, also keep in mind if the
> > >> bitstream filter API has any problems it could be changed ...
> > >>
> > >> Also note that a LATM parser or some changes to the AAC parser might
> > >> still be required even with a bitstream filter, otherwise the AAC parser
> > >> will likely be confused by the LATM stuff ...
> > >
> > > The parser needs to be modified to handle the LATM wrapping and packetize
> > > the stream. Should the parser also set the extradata so the decoder can
> > > use that to set the channels, sample rate & sample size? or should this
> > > be left to the bitstream filter?
> > >
> > > The bitstream filter should just check the LATM wrapping and remove if
> > > present.
> > >
> > > The decoder then gets raw AAC data and all the parameters have been set
> > > by the parser and so it should all work fine.
> > >
> > > Is that the plan?
> >
> > Hi Paul, Is there any update on this? the approach sounds about right
> I was waiting to hear back from one of the devs as whether this is the right 
> approach. I am keen to get this sorted ASAP as it is necessary for DVB-T here 
> in NZ.

the approach does sound ok, and extradata should be extracted via split()
and that may or may not need split() to be extended a little as its rather
primitive and simplistic now.

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

Republics decline into democracies and democracies degenerate into
despotisms. -- Aristotle
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