[FFmpeg-devel] [PATCH] avformat/hls: tag as AVFMT_TS_DISCONT

[wm4]

On Wed, 16 May 2018 11:45:58 -0700
Aman Gupta <ffmpeg at tmm1.net> wrote:

> On Wed, May 16, 2018 at 11:14 AM, wm4 <nfxjfg at googlemail.com> wrote:
> 
> > On Wed, 16 May 2018 10:17:58 -0700
> > Aman Gupta <ffmpeg at tmm1.net> wrote:
> >  
> > > From: Aman Gupta <aman at tmm1.net>
> > >
> > > HLS streams can contain discontinuities. Mark the format as such.
> > >
> > > This triggers various discontinuity fixes in lavf/utils.c and fftools
> > >
> > > Signed-off-by: Aman Gupta <aman at tmm1.net>
> > > ---
> > >  libavformat/hls.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/libavformat/hls.c b/libavformat/hls.c
> > > index 4ee4be769d..3199b0ac8d 100644
> > > --- a/libavformat/hls.c
> > > +++ b/libavformat/hls.c
> > > @@ -2277,7 +2277,7 @@ AVInputFormat ff_hls_demuxer = {
> > >      .long_name      = NULL_IF_CONFIG_SMALL("Apple HTTP Live Streaming"),
> > >      .priv_class     = &hls_class,
> > >      .priv_data_size = sizeof(HLSContext),
> > > -    .flags          = AVFMT_NOGENSEARCH,
> > > +    .flags          = AVFMT_NOGENSEARCH | AVFMT_TS_DISCONT,
> > >      .read_probe     = hls_probe,
> > >      .read_header    = hls_read_header,
> > >      .read_packet    = hls_read_packet,  
> >
> > I think I'm against this. HLS streams do not typically contain
> > timestamp resets (even if they could). Otherwise you might as well add
> >  
> 
> mpegts timestamps wrap every 26 hours, so any live continuous HLS broadcast
> is guaranteed to have a timestamp reset.
> Users have reported seeing these resets on various streams (
> http://ffmpeg.org/pipermail/ffmpeg-devel/2018-March/226706.html), plus
> the HLS spec itself defines a EXT-X-DISCONTINUITY tag to signal
> discontinuities. So I don't think it's fair to say that discontinuities
> don't typically occur and can be ignored.

Wouldn't it be better to introduce a discontinuity notification then?
Then adding the discont flag would be redundant and could be avoided.
It looks like the HLS tag would map cleanly to this.

> 
> > this flag to the Matroska demuxer. Besides, it would break some of my
> > code, which uses this flag as a heuristic to detect mpeg-ts style
> > non-container formats.
> >  
> 
> I'm working on a patchset with a new -remove_ts_discont option which will
> remove discontinuities and normalize timestamps. This
> option would only kick in for formats marked as AVFMT_TS_DISCONT, so I
> would like to see any formats where timestamp
> discontinuities are possible to be marked as such.

My suggestion would probably not block this.

> Maybe we can add another AVFMT flag that can be used as your heuristic?

Well, my heuristic is probably messed up and nonsense anyway. I'd just
find it nice if this isn't enabled to avoid currently released
versions, but I guess my argument is weak.