[FFmpeg-devel] [PATCH 2/3] flvdec: Mark the demuxer as allowing discontinuous timestamps

[Derek Buitenhuis]

On 22/11/2018 02:16, Michael Niedermayer wrote:
> the specification says this:
> "Timestamp UI24 Time in milliseconds at which the data in this tag
>                 applies. This is relative to the first tag in the FLV file,
>                 which always has a timestamp of 0.
> "
> So flv does not seem to allow discontinuities. Any tool writing files with
> discontinuities would be faulty

I know they're not valid, however in the real world, tons and tons of these files
exists, since this is how live FLV is done quite often.

> declaring files which have no discontinuities as having some would
> result in worse performing seeking in some cases. Both slower and or less
> accurate. Also flv IIRC allows gaps in tracks like no packets where there is
> silence. This may interfere with discontinuities as it looks
> like a discontinuity.

I agree, but then how do you propose we handle FLVs that do have discontinuites?
Currently the demuxer just outputs the discontinuiting (negative or positive),
and it breaks, since codebases expect that demuxers which do this will be properly
marked with the DISCONT flag.

> Can these files with discontinuities be detected somehow from the headers?
> If so then the probe function could be changed so they get the discontinuity
> flag while valid files do not have the disadvantages from having it set

As far as I am aware, no, they cannot be detected by header. FLV is crappy like that.

Every downstream codebase that cares could force the 'live_flv' demuxer for all FLVs,
but this seems ugly and needlessly special cased.

I am open to better solutions...

- Derek