Request: specify ffmpeg encoder and parameters

[ahmadrr]

I would like the ffmpeg output to be losslessly encoded using libx265 -preset ultrafast -crf 0 -pix_fmt yuv420p for further editing using different application. The current implementation when specifying .mp4 output seems to make ffmpeg use the default libx264 -preset medium -crf 23. Or add just an option to pass lossless encoding to ffmpeg would be good too.

[gar-onn]

Try editing the line in RenderIntervalThread.py