==Summary==
I've been implementing ffmpeg/libav into an application, and have run
into timing-related issues when playing back Matroska/MKV videos created
by my application in VLC. I tried asking about this on the libav-user
mailing list and received no response so I thought I'd try here. While
it's true that there may be issues with VLC's implementation too, I've
noticed specifically that videos generated by FFmpeg do not cause these
issues, while my application and the examples in "doc/examples" (which
my code is modeled from) do, which makes me think this code is missing
something crucial.
==Symptoms==
During playback, VLC's playback time will appear to stay frozen at 0:00
while the video and audio plays normally. It will then jump only in
increments of a few seconds (0:03, then 0:07, then 0:11, etc.) This
behavior occurs with videos produced both by my application and by the
FFmpeg examples programs "transcoding.c" and "remuxing.c".
The fact that this occurs with "remuxing.c" is particularly interesting
since that would seem to imply it's an issue with the format/container
writing specifically. If "remuxing.c" is given a correct MKV file (i.e.
one that does not exhibit this issue) produced by FFmpeg as its input,
and outputs to a second MKV file, that second MKV will demonstrate this
issue even though the first one didn't, indicating that something is
breaking during the remuxing process despite no decoding/encoding occurring.
The worst demonstration of this issue that I've run into is if my
application writes any audio packets before writing the first video
packet (with "av_interleaved_write_frame"), the first few seconds of
video (until that first 0:03) will be considered completely blank by
VLC. The fact that it will pick up after 0:03, the same time the timer
will make its first update on other MKV files, leads me to believe it's
the exact same root cause, just a different presentation of it.
This issue only occurs on MKV files. MP4/MOV appear to have no issues
whatsoever.
==Conclusion==
Considering FFmpeg produces correct MKV files, I don't believe this to
be a bug in libav (though it could be considered a bug in the examples).
I'm assuming the examples and my program are missing something or doing
something incorrectly.
My code can be seen here, however the examples will almost certainly be
easier to read and test:
https://github.com/olive-editor/olive/blob/master/app/codec/ffmpeg/ffmpegencoder.cpp
Thanks in advance for any help, I'm a little confused about this whole
issue.
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