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

[Michael Niedermayer]

On Thu, Nov 22, 2018 at 07:18:04PM +0200, Jan Ekström wrote:
> On Thu, Nov 22, 2018 at 4:17 AM Michael Niedermayer
> <michael at niedermayer.cc> wrote:
> >
> > On Wed, Nov 21, 2018 at 03:58:47PM +0000, Derek Buitenhuis wrote:
> > > Any FLV file, not necessarily valid, but in extremely common use for live
> > > or archived live purposes, may output discontinuous timestamps. As it currently
> > > is, only files produced by NGINX's RTMP module will be marked as supporting
> > > discontinuous timestamps, which is obviously untrue, and the fix was only
> > > ever put in place for a single bug report / file. The FLV demuxer, however
> > > will happily ingest any FLV, and output discontinuous timestamps, regardless
> > > of whether this "live" demuxer is used, making the current set of flags untrue.
> > >
> > > Add the flag to the main demuxer, as this is how it *actually* works. Lying to
> > > downstream API users about a demuxer's behavior is not OK.
> > >
> > > Also set AVFMT_NOBINSEARCH, as this should be true given discontinuous timetsamps.
> > >
> > > Signed-off-by: Derek Buitenhuis <derek.buitenhuis at gmail.com>
> > > ---
> > >  libavformat/flvdec.c | 14 ++++----------
> > >  1 file changed, 4 insertions(+), 10 deletions(-)
> >
> > 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
> 
> How do you separate FLV files that came from RTMP originally (be it
> live or VOD) from files that were "just files"?
> 
> Additionally, wasn't FLV with a time base of 1000 and a 32bit (signed
> in "file" format and unsigned in RTMP (?!?!)) time stamp. See
> 4d3dd167dfdfa2f36724f5613f05f46e3477c0d1 .
> 
> I think I'm trying to sit down and note that FLV is a colossal mess
> for everyone at this point.
> 

> >
> > 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.
> 
> Yes, timestamps jumping is valid and I don't see this being similar to
> discontinuities. The fact that ffmpeg.c doesn't like intra-stream
> timestamp jumps in case this flag is set is orthogonal to this
> specific thing IMHO.

a simple example:
0,1,2,3,4,403,404,405
these are a files timestamps, is this a discontinuity or a gap of silence?

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I know you won't believe me, but the highest form of Human Excellence is
to question oneself and others. -- Socrates
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