[FFmpeg-devel] [PATCH v7] Add SUP/PGS subtitle demuxer
Michael Niedermayer
michaelni at gmx.at
Wed Oct 1 12:58:32 CEST 2014
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.
>
> > First packet:
> >
> > pts=255314
> > pts_time=2.836822
> > dts=255314
> > dts_time=2.836822
> >
> > Second packet:
> >
> > pts=255037
> > pts_time=2.833744
> > dts=255037
> > dts_time=2.833744
>
> those dts's are generated by ffmpeg, probably in mux.c
> compute_pkt_fields2().
>
> > > 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
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
Avoid a single point of failure, be that a person or equipment.
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