demux_mkv: probe start time

MKV files can very well start with timestamps other than 0. While mpv
has support for such files in general, and demux_lavf enables this
feature, demux_mkv didn't export a start time.

Implement this by simply reading the first cluster timestamp. This in
turn is done by reading 1 block. While we don't need the block for this
prupose at all, it's the easiest way to get the cluster timestamp read
correctly without code duplication. In theory this could be wrong, and
a packet could start at a much later time, but in practice this won't
happen.

This commit also adds an option to disable this feature. It's not
documented because nobody should use it. (But I happen to have a need
for this.)

0 files changed, 0 insertions, 0 deletions