[FFmpeg-devel] [PATCH] lavf/matroskadec: fix is_keyframe for early Blocks
nfxjfg at googlemail.com
Fri Feb 3 08:16:45 EET 2017
On Thu, 2 Feb 2017 10:47:52 -0800
Vignesh Venkatasubramanian <vigneshv-at-google.com at ffmpeg.org> wrote:
> On Tue, Jan 31, 2017 at 10:18 PM, wm4 <nfxjfg at googlemail.com> wrote:
> > On Tue, 31 Jan 2017 12:02:01 -0800
> > Chris Cunningham <chcunningham at chromium.org> wrote:
> > > Thanks for taking a look.
> > >
> > > Definitely missing a "break;" - will fix in subsequent patch.
> > >
> > > Agree timestamps should be relative (didn't realize this). Vignesh points
> > > out that "0" in the test file is due to a bug in ffmpeg (and probably other
> > > muxers) where this value is not written as a relative timestamp, but
> > > instead as the timestamp of the previous frame. https://github.com/FFmp
> > > eg/FFmpeg/blob/master/libavformat/matroskaenc.c#L2053
> > > <https://www.google.com/url?q=https%3A%2F%2Fgithub.com%2FFFmpeg%2FFFmpeg%2Fblob%2Fmaster%2Flibavformat%2Fmatroskaenc.c%23L2053&sa=D&sntz=1&usg=AFQjCNGs8m6GsWbhTvCZl0Q_juGAldQblA>
> > Just a few lines below this reads
> > mkv->last_track_timestamp[track_number - 1] = ts - mkv->cluster_pts;
> > which looks like it intends to write a relative value. Though "ts" can
> > be a DTS, while the other value is always a PTS.
> Just to clarify: This line makes the timestamp relative to the
> cluster's timestamp. Not relative to the block its referencing (which
> is what the spec says if i understand it correctly).
Yeah, the current spec just says "Timestamp of another frame used as a
reference (ie: B or P frame). The timestamp is relative to the block
it's attached to."
Is this a bug? Did FFmpeg always mux this incorrectly?
Is there even an implementation that uses the value written to block
reference elements? (And not in a trivial way like FFmpeg.)
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