[FFmpeg-devel] [PATCH v7] Add SUP/PGS subtitle demuxer
Michael Niedermayer
michaelni at gmx.at
Wed Oct 1 17:11:17 CEST 2014
On Wed, Oct 01, 2014 at 03:07:19PM +0200, wm4 wrote:
> On Wed, 1 Oct 2014 12:58:32 +0200
> Michael Niedermayer <michaelni at gmx.at> wrote:
>
> > On Wed, Oct 01, 2014 at 01:36:58PM +0300, Petri Hintukainen wrote:
> > > On ti, 2014-09-30 at 16:09 +0200, wm4 wrote:
> > > > On Tue, 30 Sep 2014 12:01:33 +0300
> > > > Petri Hintukainen <phintuka at gmail.com> wrote:
> > > >
> > > > > Hello,
> > > > >
> > > > > Missing DTS combined with non-monotonic PTS seems to cause some
> > > > > problems. This is with the file from ticket #2208 (I added dumping
> > > > > timestamps to demuxer and muxer):
> > > > >
> > > > >
> > > > > $ ../ffmpeg -i orig/track_06\ -\ Subtitle.sup -scodec copy 6.sup
> > > > > ffmpeg version N-66546-gea74007 Copyright (c) 2000-2014 the FFmpeg
> > > > > developers
> > > > > built on Sep 30 2014 11:10:08 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
> > > > > configuration:
> > > > > libavutil 54. 7.101 / 54. 7.101
> > > > > libavcodec 56. 1.101 / 56. 1.101
> > > > > libavformat 56. 7.101 / 56. 7.101
> > > > > libavdevice 56. 1.100 / 56. 1.100
> > > > > libavfilter 5. 1.102 / 5. 1.102
> > > > > libswscale 3. 1.100 / 3. 1.100
> > > > > libswresample 1. 1.100 / 1. 1.100
> > > > > IN pts 00255314 dts 00000000
> > > > > Input #0, sup, from 'orig/track_06 - Subtitle.sup':
> > > > > Duration: N/A, start: 2.836822, bitrate: N/A
> > > > > Stream #0:0: Subtitle: hdmv_pgs_subtitle, 1920x1080
> > > > > Output #0, sup, to '6.sup':
> > > > > Metadata:
> > > > > encoder : Lavf56.7.101
> > > > > Stream #0:0: Subtitle: hdmv_pgs_subtitle, 1920x1080
> > > > > Stream mapping:
> > > > > Stream #0:0 -> #0:0 (copy)
> > > > > Press [q] to stop, [?] for help
> > > > > OUT pts 00000000 dts 00000000
> > > > > IN pts 00255037 dts 00000000
> > > > > OUT pts 00000000 dts 00000000
> > > > > IN pts 00249205 dts 00000000
> > > > > [sup @ 0x241f4e0] Application provided invalid, non monotonically
> > > > > increasing dts to muxer in stream 0: -277 >= -6109
> > > > > av_interleaved_write_frame(): Invalid argument
> > > > > size= 0kB time=00:00:00.00 bitrate=N/A
> > > > > video:0kB audio:0kB subtitle:1kB other streams:0kB global headers:0kB
> > > > > muxing overhead: unknown
> > > > > Conversion failed!
> > > >
> > > > The DTS in this file are indeed decreasing sometimes.
> > >
> > > No, there are no DTS timestamps in this file.
>
>
> > > those dts's are generated by ffmpeg, probably in mux.c
> > > compute_pkt_fields2().
that could be
>
> Ouch. Yeah, I think this function used to corrupt perfectly fine h264
> mpegts timestamps in the past or so...
which trac ticket is that ?
or do you mean by "past" that this is not relevant anymore as it has
been fixed already ?
>
> > > > > Also note that timestamps are re-positioned to start from 0. This may be
> > > > > problematic, it requires manually synchronizing subtitles to the video.
> > > >
> > > > "Rebasing" the timestamps is apparently the normal operation of
> > > > ffmpeg.c, there's probably a way to make it stop doing that.
> > >
> > > Yes, -copyts seems to do the trick.
> > > I think all pts timestamps in .sup file should be relative to video
> > > start, i.e. if video starts at pts 12345, corresponding .sup file starts
> > > at pts = pts_of_first_subtitle - 12345.
> > >
> > > > > Remuxing from the original .m2ts file works just well:
> > > > >
> > > > >
> > > > > $ ffmpeg -i orig/00038.m2ts -map 0:6 -scodec copy 6.sup
> > > > > ffmpeg version N-66546-gea74007 Copyright (c) 2000-2014 the FFmpeg developers
> > > > > built on Sep 30 2014 11:10:08 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
> > > > > configuration:
> > > > > libavutil 54. 7.101 / 54. 7.101
> > > > > libavcodec 56. 1.101 / 56. 1.101
> > > > > libavformat 56. 7.101 / 56. 7.101
> > > > > libavdevice 56. 1.100 / 56. 1.100
> > > > > libavfilter 5. 1.102 / 5. 1.102
> > > > > libswscale 3. 1.100 / 3. 1.100
> > > > > libswresample 1. 1.100 / 1. 1.100
> > > > > [NULL @ 0x1bf9ba0] start time for stream 6 is not set in estimate_timings_from_pts
> > > > > [NULL @ 0x1c146e0] start time for stream 7 is not set in estimate_timings_from_pts
> > > > > [NULL @ 0x1c151c0] start time for stream 8 is not set in estimate_timings_from_pts
> > > > > [mpegts @ 0x1bf1ca0] Could not find codec parameters for stream 6 (Subtitle: hdmv_pgs_subtitle ([144][0][0][0] / 0x0090)): unspecified size
> > > > > Consider increasing the value for the 'analyzeduration' and 'probesize' options
> > > > > [mpegts @ 0x1bf1ca0] Could not find codec parameters for stream 7 (Subtitle: hdmv_pgs_subtitle ([144][0][0][0] / 0x0090)): unspecified size
> > > > > Consider increasing the value for the 'analyzeduration' and 'probesize' options
> > > > > [mpegts @ 0x1bf1ca0] Could not find codec parameters for stream 8 (Subtitle: hdmv_pgs_subtitle ([144][0][0][0] / 0x0090)): unspecified size
> > > > > Consider increasing the value for the 'analyzeduration' and 'probesize' options
> > > > > Input #0, mpegts, from 'orig/00038.m2ts':
> > > > > Duration: 00:00:43.90, start: 11.650667, bitrate: 35145 kb/s
> > > > > Program 1
> > > > > Stream #0:0[0x1011]: Video: h264 (High) (HDMV / 0x564D4448), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 23.98 fps, 23.98 tbr, 90k tbn, 47.95 tbc
> > > > > Stream #0:1[0x1100]: Audio: truehd (AC-3 / 0x332D4341), 48000 Hz, 7.1, s32 (24 bit)
> > > > > Stream #0:2[0x1100]: Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, 5.1(side), fltp, 640 kb/s
> > > > > Stream #0:3[0x1101]: Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, stereo, fltp, 320 kb/s
> > > > > Stream #0:4[0x1102]: Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, stereo, fltp, 320 kb/s
> > > > > Stream #0:5[0x1200]: Subtitle: hdmv_pgs_subtitle ([144][0][0][0] / 0x0090), 1920x1080
> > > > > Stream #0:6[0x1201]: Subtitle: hdmv_pgs_subtitle ([144][0][0][0] / 0x0090)
> > > > > Stream #0:7[0x1202]: Subtitle: hdmv_pgs_subtitle ([144][0][0][0] / 0x0090)
> > > > > Stream #0:8[0x1203]: Subtitle: hdmv_pgs_subtitle ([144][0][0][0] / 0x0090)
> > > > > Output #0, sup, to '6.sup':
> > > > > Metadata:
> > > > > encoder : Lavf56.7.101
> > > > > Stream #0:0: Subtitle: hdmv_pgs_subtitle ([144][0][0][0] / 0x0090)
> > > > > Stream mapping:
> > > > > Stream #0:6 -> #0:0 (copy)
> > > > > Press [q] to stop, [?] for help
> > > > > OUT pts 00255255 dts 00249146
> > > > > OUT pts 00254978 dts 00249146
> > > > > OUT pts 00249146 dts 00249146
> > > > > OUT pts 00249699 dts 00249146
> > > > > OUT pts 00249699 dts 00249699
> > > > > ...
> > > > >
> > > > >
> > > > > Also, remuxing this file again (.sup->.sup) with ffmpeg works. Well,
> > > > > except that timestamps are again repositioned.
> > > > >
> > > > >
> > > > > Is this something that can be handled in muxer ?
> > > >
> > > > Not sure what's going on here at all. Normally, DTS as stored in a file
> > > > should never decrease, except on timestamp resets, which doesn't happen
> > > > here.
> > >
> > > ffmpeg uses PTS as DTS when there is no DTS. This does not work well
> > > with non-monotonic PTS (that's why DTS should be kept in those
> > > files ...). I think there are also some players that do not display PGS
> > > subtitles without DTS.
> > >
> > > Using AVFMT_NOTIMESTAMPS in .sup muxer kind of works, but incorrect DTS
> > > is still written to output file, and there are lot of error messages. I
> > > could probably hack the muxer to drop those invalid DTS timestamps, but
> > > it doesn't feel the right solution (and does not work with other output
> > > formats).
> > >
> > > One possible solution in demuxer (or parser) could be reading all
> > > segments until segment 0x80 is found, and using the smallest PTS value
> > > found as DTS for every segment in display set. I'm not sure if this
> > > would be 100% compilant, but I can try to check it.
> > > In any case, there's no way one could guess/calculate DTS from PTS of
> > > first segment. Some upper limit / "safety distance" for PTS-DTS
> > > difference could possibly be found from full-screen display update, but
> > > I don't know if that could cause overflowing graphics buffers with high
> > > frame rate animations.
> > >
> > > Probably the best solution would be to not output DTS when it is not
> > > present in input (and maybe refusing to mux such files to containers
> > > that require DTS), but I have no idea how to implement it :)
> >
> > i didnt follow this thread closely but
> > why is this dts calculation so hard ?
> > consider a matching encoder, how would it generate DTS ?
> > it has to, to function, a encoder just has pts and durations for its
> > raw input and needs dts on its output encoded bitstream packets
>
> If we can't reconstruct a correct DTS if it's missing, we definitely
> should prevent the generic libavformat code from filling in completely
> broken DTS. Is there a flag for this?
dts are not optional in mpeg*
if you have no dts you wont have a mpeg-TS
They are a integral part of the muxing process
used both in the buffering model as well as in stream interleaving.
that said its quite easy to add a flag to disable the code that
sets the DTS if someone really wants such flag
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
Awnsering whenever a program halts or runs forever is
On a turing machine, in general impossible (turings halting problem).
On any real computer, always possible as a real computer has a finite number
of states N, and will either halt in less than N cycles or never halt.
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