[FFmpeg-devel] [PATCH]Fix AC3-in-avi for the remaining cases

[Michael Niedermayer]

On Sat, Jan 01, 2011 at 03:52:07PM -0500, Justin Ruggles wrote:
> On 01/01/2011 03:03 PM, Carl Eugen Hoyos wrote:
> 
> > Hi!
> > 
> > Current svn produces avi files that don't playback on any player when muxing 
> > AC3 with 32kHz/320kB, 32kHz/384kB and 44.1kHz/384kB.
> > I believe Justin suggested to set blkalign to maximum frame size (first 
> > patch).
> > An alternative is to just fix the failing cases (second patch).
> > 
> > Opinions?
> > 
> > Please comment, Carl Eugen
> > 
> > 
> 
> > Index: libavformat/riff.c
> > ===================================================================
> > --- libavformat/riff.c	(revision 26183)
> > +++ libavformat/riff.c	(working copy)
> > @@ -370,12 +370,10 @@
> >          av_log(enc, AV_LOG_WARNING, "requested bits_per_coded_sample (%d) and actually stored (%d) differ\n", enc->bits_per_coded_sample, bps);
> >      }
> >  
> > -    if (enc->codec_id == CODEC_ID_MP2 || enc->codec_id == CODEC_ID_MP3 || enc->codec_id == CODEC_ID_AC3) {
> > +    if (enc->codec_id == CODEC_ID_MP2 || enc->codec_id == CODEC_ID_MP3) {
> >          blkalign = enc->frame_size; //this is wrong, but it seems many demuxers do not work if this is set correctly
> >          //blkalign = 144 * enc->bit_rate/enc->sample_rate;
> > -        //For high bitrate AC-3, set blkalign to maximum bytes per frame value
> > -        //to allow playback on WMP and MPlayer
> > -        if (enc->bit_rate > 384000)
> > +    } else if (enc->codec_id == CODEC_ID_AC3) {
> >              blkalign = 3840;
> >      } else if (enc->codec_id == CODEC_ID_ADPCM_G726) { //
> >          blkalign = 1;
> 
> 
> I like this version better.
> 
> Regarding the other patch, if it would be better for some reason to use
> a more accurate value for AC-3 we could do:

being exact when there is exactly just 1 packet size is nice, beyond that its
a hack either way


> 
> switch (enc->sample_rate) {
>      8000: blkalign =  960;
>     11025: blkalign =  697;
>     12000: blkalign =  640;
>     16000: blkalign = 1920;
>     22050: blkalign = 1394;
>     24000: blkalign = 1280;
>     32000: blkalign = 3840;
>     44100: blkalign = 2788;
>     48000: blkalign = 2560;
> }

Is this how our encoder behaves or is this required by spec?



[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

There will always be a question for which you do not know the correct awnser.
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