[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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