Video sync via GstClock

[Marc Leeman]

> What i try to do: Two videos (master and slave) should play to the
> millisecond. But the play always at their own clock...

You need to provide more details, I've done a setup like that several
times and it just works; both form network and from file.

e.g. just the other day; we had 4 TS files playing in sync and another
test where decoders lock on to a network source and play off in sync.