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Try to use any video converter and convert your files to constant frame rate.
Handbrake, movavi video converter, ffmpeg, xvid4psp or any other.
For ffmpeg your command line will be similar:
ffmpeg -i "input-file-name.mov" -r 25 "output-file-name.mov"
-r 25 - it's a framerate.
Mediainfo should show constant frame rate after render.
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