[FFmpeg-devel] [PATCH] mov.c: allow reading fragment start dts/pts from fragmented mp4

Sat Oct 11 22:02:54 CEST 2014

On Sat, Oct 11, 2014 at 08:38:14PM +0300, Mika Raento wrote:
> On 11 October 2014 20:20, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Sat, Oct 11, 2014 at 06:43:48PM +0300, Mika Raento wrote:
> >> This introduces a new option to the mov demuxer: -use_mfra_for
> >> (pts|dts). When it's given and moofs and a MFRA are present, the MFRA's
> >> TFRAs are read for fragment start times.
> >>
> >> Unfortunately some programs that produce fragmented mp4s use the TFRA
> >> time field for dts and some for pts. There is no realistic way to detect
> >> which is the case, hence the responsibility is punted onto the user.
> >> This also means that no behavioural change is enabled by default - you
> >> must pass either dts or pts for anything to happen.
> >>
> >> Without this change, timestamps for some discontinuous fragmented mp4 are
> >> wrong, and cause audio/video desync and are not usable for generating
> >> HLS.
> >> ---
> > [...]
> >> @@ -3943,6 +4111,15 @@ static const AVOption options[] = {
> >>          0, 1, AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_DECODING_PARAM},
> >>      {"ignore_editlist", "", offsetof(MOVContext, ignore_editlist), FF_OPT_TYPE_INT, {.i64 = 0},
> >>          0, 1, AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_DECODING_PARAM},
> >> +    {"use_mfra_for",
> >> +        "use mfra for fragment timestamps",
> >> +        offsetof(MOVContext, use_mfra_for), FF_OPT_TYPE_INT, {.i64 = 0},
> >> +        0, FF_MOV_FLAG_MFRA_PTS, AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_DECODING_PARAM,
> >> +        "use_mfra_for"},
> >
> > maybe a FF_MOV_FLAG_MFRA_AUTO which is set by default could be used to
> > guess based on some encoder/muxer identification what to do.
> >
> > do the files which need this option have something that idenifies
> > them? like in metadata, compatible brands or other?
> > and can you share a file/testcase which needs this patch ?
> 
> I can share a file privately (copyrighted). I do not have a reduced
> test case. Let me know if you think that's helpful.

dunno, might be usefull


> 
> The files come from a commercial packager that is getting
> discontinuous input from a commercial transcoder. My understanding is
> that, the timestamp issue comes from the packager, rather than the
> transcoder. The underlying software in the packager is Code-shop's
> Unified Streaming, but it's been fed from proprietary software.
> 
> This is what ffprobe says, it's not very specific:
> 
> (multiprofile-streamers)mikie at universe:~/devel/multiprofile-streamers$
> ffprobe -i ../multiprofile-fixer/hls-disco/50603088.ismv
> ffprobe version N-66765-g67d95df Copyright (c) 2007-2014 the FFmpeg developers
>   built on Oct 11 2014 18:42:41 with Apple LLVM version 6.0
> (clang-600.0.51) (based on LLVM 3.5svn)
>   configuration: --prefix=/usr/local/Cellar/ffmpeg/HEAD
> --enable-shared --enable-pthreads --enable-gpl --enable-version3
> --enable-nonfree --enable-hardcoded-tables --enable-avresample
> --enable-vda --cc=clang --host-cflags= --host-ldflags=
> --enable-libx264 --enable-libfaac --enable-libmp3lame --enable-libxvid
> --enable-debug --disable-stripping --enable-libass
>   libavutil      54. 10.100 / 54. 10.100
>   libavcodec     56.  4.101 / 56.  4.101
>   libavformat    56.  9.100 / 56.  9.100
>   libavdevice    56.  1.100 / 56.  1.100
>   libavfilter     5.  1.103 /  5.  1.103
>   libavresample   2.  1.  0 /  2.  1.  0
>   libswscale      3.  1.100 /  3.  1.100
>   libswresample   1.  1.100 /  1.  1.100
>   libpostproc    53.  1.100 / 53.  1.100
> Input #0, mov,mp4,m4a,3gp,3g2,mj2, from
> '../multiprofile-fixer/hls-disco/50603088.ismv':
>   Metadata:
>     major_brand     : isom
>     minor_version   : 1
>     compatible_brands: isomiso2
>   Duration: 02:17:00.14, start: 0.000000, bitrate: 4411 kb/s
>     Stream #0:0(mul): Audio: aac (mp4a / 0x6134706D), 48000 Hz,
> stereo, fltp, 124 kb/s (default)
>     Metadata:
>       handler_name    : Sound Handler
>     Stream #0:1(mul): Audio: aac (mp4a / 0x6134706D), 48000 Hz,
> stereo, fltp, 29 kb/s (default)
>     Metadata:
>       handler_name    : Sound Handler
>     Stream #0:2(und): Video: h264 (Main) (avc1 / 0x31637661),
> yuv420p(tv, bt470bg), 480x270 [SAR 1:1 DAR 16:9], 597 kb/s, 25 fps, 25
> tbr, 10000k tbn, 50 tbc (default)
>     Metadata:
>       handler_name    : Video Handler
>       encoder         : AVC Coding
>     Stream #0:3(und): Video: h264 (Main) (avc1 / 0x31637661),
> yuv420p(tv, bt470bg), 640x360 [SAR 1:1 DAR 16:9], 1195 kb/s, 25 fps,
> 25 tbr, 10000k tbn, 50 tbc (default)
>     Metadata:
>       handler_name    : Video Handler
>       encoder         : AVC Coding
>     Stream #0:4(und): Video: h264 (High) (avc1 / 0x31637661),
> yuv420p(tv, bt470bg), 768x432 [SAR 1:1 DAR 16:9], 2487 kb/s, 25 fps,
> 25 tbr, 10000k tbn, 50 tbc (default)
>     Metadata:
>       handler_name    : Video Handler
>       encoder         : AVC Coding
> 
> 
> >
> > Also ISO/IEC 14496-12:2008(E) seems to say this:
> >     This box provides only a hint as to where random access points are; the movie fragments themselves are
> >     definitive. It is recommended that readers take care in both locating and using this box as modifications to the
> >     file after it was created may render either the pointers, or the declaration of random access points, incorrect.
> >
> > so if i understand it correctly, using these boxes requires some care
> > like maybe checking for some brand or muxer/encoder which makes further
> > gurantees about their validity.
> 
> From the differences between the packagers and the different
> interpretations of the spec, I'm not very eager to attempt
> autodetection.
> 
> Consider ffmpeg: we'll at some point change the fragmentation code to
> use pts. Whether that'll be visible in the file metadata is unclear.

LIBAVFORMAT_IDENT will change as the version will change


[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Dictatorship naturally arises out of democracy, and the most aggravated
form of tyranny and slavery out of the most extreme liberty. -- Plato
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