Multithread framerate problem

[provalinf]

Hi,

I've noticed a problem over the last few months, when you select the multithreaded option, the original framerate is no longer respected (which causes a sound delay on long sequences of course).

Original:

Split:

Output:

No problem on singlethread.

File test: https://user-images.githubusercontent.com/15704455/140654531-2aed8cc4-545d-415b-9734-31edd5fc7adc.mp4