sub2video overlay fails with negative starting timestamp and -copyts

[Mika Raento]

Summary of the bug: If the input starts on a negative time and -copyts is given, sub2video causes 'Buffer queue overflow, dropping' messages and broken output.

Although this seems like a minor problem, the problem is easily triggered by broadcast input that has non-monotonic timestamps (will try to find a simple testcase for that and file a separate ticket).

I need -copyts to later sync video and audio if there is missing video or audio.

How to reproduce:

$ ffmpeg -y -i negative_pts_sub.ts -copyts -filter_complex '[0:0][0:3]overlay[outv0]' -map 0:1 -map '[outv0]' broken.ts
ffmpeg version N-67065-g2fa08fd Copyright (c) 2000-2014 the FFmpeg developers
  built on Oct 23 2014 08:58:30 with Apple LLVM version 6.0 (clang-600.0.51) (based on LLVM 3.5svn)

The following works:

$ ffmpeg -y -itsoffset 46.944644 -i negative_pts_sub.ts -copyts -filter_complex '[0:0][0:3]overlay[outv0]' -map 0:1 -map '[outv0]' working.ts

Patches should be submitted to the ffmpeg-devel mailing list and not this bug tracker.

[Carl Eugen Hoyos]

Please provide the input sample and the complete, uncut console output of the failing command to make this a valid ticket.

[Mika Raento]

log file from non-working comamnd

[Mika Raento]

log file from working command

[Mika Raento]

uploaded the input file to upload.ffmpeg.org/incoming

[Carl Eugen Hoyos]

Does the sample you uploaded contain any subtitles? How can I see them?

[Mika Raento]

Replying to cehoyos:

Does the sample you uploaded contain any subtitles? How can I see them?

The cut-down version does not contain any subtitles that would be visible.

$ ffprobe -i negative_pts_sub.ts -select_streams s -show_packets

will show you that there are subtitle packets.

Do you want a larger sample that contains visible subtitles?

[Carl Eugen Hoyos]

Imo, even if the issue is reproducible without visible subtitles, it makes the issue (your issue) easier to understand if there are subtitles visible.

[Mika Raento]

Uploaded negative_pts_sub_long.ts to upload.ffmpeg.org/incoming

There are Finnish subtitles from 03min04s, viewable in VLC or by running the 'working' example command with this file (the subtitles are not scaled right, I didn't put that in the command for this ticket).

[Cigaes]

Thanks for the bug report and the sample. Can you test whether the following patch fixes the problem for you?
​http://ffmpeg.org/pipermail/ffmpeg-devel/2014-November/164811.html

The problem is with the heartbeat for the subtitles; since subtitles streams are sparse, overlay needs a heartbeat frame to know that subtitles have not changed and have a timestamp. The initial value for the heartbeat was left to 0, and video frames with negative timestamps would not generate heartbeat. The solution is to init it to -∞ or equivalent.

[Mika Raento]

Thanks! Will take a look.

[Mika Raento]

Yes, the patch fixes this problem. Thank you!

[Michael Niedermayer]

Fixed by Nicolas in 90cdec5e2698973fdb6643c1d66c7254478929f3