SubRip subtitles to TX3G problems when the millisecond in the presentation timestamp are not a multiple of 10

[pdamont]

Summary of the bug:
I have the exact 2 same subtitles in sub rib (.srt) format.

• One (not-rounded.srt) has timestamp in the form:

00:00:00,991 --> 00:00:03,227

• The other one (rounded.srt) is the same but with rounded timestamp (no millisecond, only multiples of 10 ms):

00:00:00,990 --> 00:00:03,230

When I encode a MP4 movie including one or the other subtitles, in QuickTime or iPad or iPhone, only the resulting movie with rounded subtitles shows every subtitles. When it's not rounded, only the first subtitle is displayed.

Here is the command line:
ffmpeg -i source.mp4 -i rounded.srt -c:v copy -c:a copy -c:s mov_text -metadata:s language=eng rounded.mp4

I extracted the TX3G subtitles using MP4Box:
MP4Box -ttxt 3 rounded.mp4
MP4Box -ttxt 3 not-rounded.mp4

and I can see surprising results: when it's not rounded, the timestamps are unordered, and blank subtitles are in fact preventing the subtitles to be displayed, for instance:

• not-rounded_3_text.ttxt:

<TextSample sampleTime="00:00:03.231" xml:space="preserve"></TextSample>
<TextSample sampleTime="00:00:03.228" xml:space="preserve">that she absolutely loved,</TextSample>

• rounded_3_text.ttxt:

<TextSample sampleTime="00:00:03.230" xml:space="preserve"></TextSample>
<TextSample sampleTime="00:00:03.230" xml:space="preserve">that she absolutely loved,</TextSample>

So right now to soft encode subtitles I first encode my srt to ass with one ffmpeg command (subrip -> ass conversion), and then use the ass subtitles instead (ass -> mov_text mapping). I do that because I have noticed the srt->ass conversion rounds timestamp. But it's a shame, because I should be able to use directly (subrip -> mov_text) even with srt file which have precise timestamps up to the millisecond.

Attached are the ttxt output from mp4box and the srt files.

Since the ttxt output is wrong (unordered and blank text displayed right after actual subtitles), I believe there is a bug here.

[Carl Eugen Hoyos]

Is the problem reproducible with current FFmpeg git head?
Please provide the failing command line together with the complete, uncut console output.

[pdamont]

Problem seems solved (subtitles appear) with version 2.6.0, however I get a lot of warnings like this one:

[mp4 @ 0x7fe1e2034200] Application provided duration: -3 / timestamp: 2161710 is out of range for mov/mp4 format
[mp4 @ 0x7fe1e2034200] pts has no value

Command line was:

ffmpeg  -i input.mkv  -i sub.srt -c:v copy -c:a copy -c:s mov_text output.mp4

I have to add -fix_sub_duration to remove them:

ffmpeg  -i input.mkv  -fix_sub_duration -i sub.srt -c:v copy -c:a copy -c:s mov_text output.mp4