[Kdenlive-devel] jack mlt transport sync issues

[Ed Rogalsky]

Hi Dan,

the last days I did a lot of jack transport sync tests and found the
following behaviour:

For frame rates unequal 25 fps the mlt playback is deverging pretty fast.
In about 3-5s
I get a difference of a frame and so on. Only for 25 fps the mlt playback
speed and jack
is in sync. And this is curious:

I know the mlt - jack clocks are not synchronized => (minor) sync issues
are expected and if "mlt's
clock" is running faster => for all frame rates mlt would play faster. Fact
is that only fps != 25
are faster and this is what I don't understand. I didn't parse the code but
I think there is something systematic - relative time calculation and
optimistic rounding ...???

Any ideas?


The fact is that the mlt clock is not synced with jack. This would be not
so critical if the deverging speed would be less or null. For now the
running transport sync is too bad for use. And this problem is only
solveble if the two clocks are synced in some way :-((( Or there are some
tricks?????


BTW: The audio frequecy is 48kHz and I work close together with Robin
Gareus. He's implementing the video timeline in ardour3.


PS: Do we have a chance to drop frames or "sync speed" based on an external
clock like jack
in mlt? I know adding this is absolutely not trivial :-((

regards

eddrog
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