[FFmpeg-devel] [PATCH] Add a parser for DNET (byte-swapped AC3).

[Reimar Döffinger]

On Wed, Mar 02, 2011 at 09:23:17PM +0100, Kostya wrote:
> On Wed, Mar 02, 2011 at 08:12:15PM +0000, M?ns Rullg?rd wrote:
> > Reimar D?ffinger <Reimar.Doeffinger at gmx.de> writes:
> > 
> > > Currently we simply byte-swap DNET directly in the Real demuxer,
> > > however this is not generally possible/correct since which two bytes we
> > > need to swap depends on whether the header starts on an even or an odd
> > > byte.
> > > Not useful on its own within FFmpeg, but could e.g. be used together
> > > with a byte-swap bitstream filter or a modified AC3-decoder to implement
> > > more robust DNET support.
> > 
> > Where does the name DNET come from?
> > 
> > > @@ -390,6 +390,7 @@ enum CodecID {
> > >      CODEC_ID_BINKAUDIO_DCT,
> > >      CODEC_ID_AAC_LATM,
> > >      CODEC_ID_QDMC,
> > > +    CODEC_ID_DNET,
> > 
> > I don't think a new codec ID is called for.  Couldn't it be handled the
> > same way as byte-swapped DTS?
> 
> I think it can and should - and there's AC3-in-WAV too to be supported.

AC3 has only about 17 bits to identify a header on (compared to 32 or more for DTS/DCA).
Searching for a byte-swapped variant is far too likely to result in false positives
to be acceptable.