[Ffmpeg-devel] [RFC] mp4 object types comments

Michael Niedermayer michaelni
Sat Mar 24 18:50:12 CET 2007


Hi

On Sat, Mar 24, 2007 at 02:44:41PM +0000, M?ns Rullg?rd wrote:
> Baptiste Coudurier <baptiste.coudurier at smartjog.com> writes:
> 
> > Hi
> >
> > M?ns Rullg?rd wrote:
> >> Baptiste Coudurier <baptiste.coudurier at smartjog.com> writes:
> >> 
> >>> Hi
> >>>
> >>> Here are some modifications to mp4 object types Im not sure, can someone
> >>> confirm that 13818-3 can be decoded with MP2 id ?
> >> 
> >> 13818-3 extends 11172-3 (MPEG1 audio) with lower sampling rates and
> >> more channels.  An 11172-3 decoder will correctly decode basic stereo
> >> from a 13818-3 stream.  There are 3 defined layers corresponding to
> >> those in 11172-3.
> >> 
> >>> Index: libavformat/isom.c
> >>> ===================================================================
> >>> --- libavformat/isom.c	(revision 8491)
> >>> +++ libavformat/isom.c	(working copy)
> >>> @@ -25,7 +25,7 @@
> >>>  #include "riff.h"
> >>>  #include "isom.h"
> >>>  
> >>> -/* http://gpac.sourceforge.net/tutorial/mediatypes.htm */
> >>> +/* http://www.mp4ra.org */
> >>>  const AVCodecTag ff_mov_obj_type[] = {
> >>>      { CODEC_ID_MPEG4     ,  32 },
> >>>      { CODEC_ID_H264      ,  33 },
> >> 
> >> This hunk is OK, assuming the URL is relevant.
> >> 
> >>> @@ -39,10 +39,10 @@
> >>>      { CODEC_ID_AAC       , 102 }, /* MPEG2 AAC Main */
> >>>      { CODEC_ID_AAC       , 103 }, /* MPEG2 AAC Low */
> >>>      { CODEC_ID_AAC       , 104 }, /* MPEG2 AAC SSR */
> >>> -    { CODEC_ID_MP3       , 105 },
> >>> -    { CODEC_ID_MPEG1VIDEO, 106 },
> >>> -    { CODEC_ID_MP2       , 107 },
> >>> -    { CODEC_ID_MJPEG     , 108 },
> >>> +    { CODEC_ID_MP2       , 105 }, /* 13818-3 */
> >>> +    { CODEC_ID_MPEG1VIDEO, 106 }, /* 11172-2 */
> >>> +    { CODEC_ID_MP3       , 107 }, /* 11172-3 */
> >>> +    { CODEC_ID_MJPEG     , 108 }, /* 10918-1 */
> >>>      { CODEC_ID_PCM_S16LE , 224 },
> >>>      { CODEC_ID_VORBIS    , 221 },
> >>>      { CODEC_ID_QCELP     , 225 },
> >> 
> >> This mixes addition of comments with actual changes.  The added
> >> comments are fine.  The changed codec IDs are not.  All MPEG audio
> >> should use CODEC_ID_MP3.  Please make it so, but add the other two
> >> comments separately.
> >
> > Yes. About codec_id, are you sure?
> 
> See the comment in avcodec.h, line 210.
> 
> > Different tags are needed if codec_id is MP2 or MP3, and when stream
> > copying codec_id is not changed/altered.
> 
> Both 11172-3 and 13818-3 define layers 1, 2 and 3.  The tag does not
> specify which layer is used, only which standard, so CODEC_ID_MP3 is
> the only safe choice.  As 13818-3 is an extension to 11172-3, it
> should really be assigned its own codec_id.  Until we have a decoder
> for these extensions, the best choice is to use CODEC_ID_MP3.

our mp3 decoder should support these extensions, do you suggest that we
add a dummy codec_id for it? if so iam not opposed ...

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Freedom in capitalist society always remains about the same as it was in
ancient Greek republics: Freedom for slave owners. -- Vladimir Lenin
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