[FFmpeg-devel] [PATCH 2/3] lavf/srtdec: Permit streaming input

[Paul B Mahol]

On Sat, Mar 30, 2024 at 9:31 AM Tomas Härdin <git at haerdin.se> wrote:

> lör 2024-03-30 klockan 00:35 +0100 skrev Michael Niedermayer:
> > breaks fate here:
> >
> > --- ./tests/ref/fate/sub-srt-madness-timeshift  2024-03-29
> > 20:43:34.617419731 +0100
> > +++ tests/data/fate/sub-srt-madness-timeshift   2024-03-30
>
> Sorry but this file is utter crap and shouldn't be part of FATE. Look
> at this:
>
> > 53
> > 00:00:01,111 --> 00:00:02,222
> > okay, let's make things easy
> >
> > 21 lol jk
> > 00:00:03,333 --> 00:00:04,444
> > hello
> > 5
> >
> >
> > don't forget me.
> > 3
> >
> >
> > 00:00:05,555 --> 00:00:06,666
> >
> >
> > no.
> > let's add some fun
> > 44 yes we can
> > 00:00:07,777 --> 00:00:06,666
> > let's do it in reverse bc wtf not
> >
>
> This file is crafted to test srtdec as it is, rather than following
> what passes for an SRT spec (that doom9 forum post[1] and the videolan
> wiki[2]). We should remove it, or keep it as a sample that should fail
> parsing.
>
> More interesting is fate-sub-srt-badsyntax. Despite the name it doesn't
> really have bad syntax, but its cues are in a random order. I guess it
> exists to test the cue sorting logic. But should subtitle demuxers
> really sort subtitles in this way? We don't do that for other formats
> that can have non-decreasing timestamps. For comparison, the WebVTT
> spec explicitly disallows decreasing timestamps. I also wonder how this
> file was created. My guess is "via a text editor" since it seems to
> consist of bits from different SRT files. There's little reason to
> support such deliberately broken files, at least having a bunch of
> sorting logic just for it. There's no reason we couldn't output packets
> in stored order.
>
> The rest of the subtitle test cases pass.
>

I agree, current subtitles not being handled in streamed way is bad
practice.
If some subtitle have wrong order of items, than new generic subtitle
filter could be implemented
which would fix that by either using queue or seeking around in subtitle
stream.


>
> /Tomas
>
> [1] https://forum.doom9.org/showthread.php?p=470941#post470941
> [2] https://wiki.videolan.org/SubRip/
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