Container and codec limitation notification

[tin2tin]

I noticed that Parallel Render will only work with the mpeg-4 container and a h.264 codec when using Ffmpeg video. I guess, that this is not a bug, but probably a limitation. Apparently, ffmpeg does not have a codec limitation when concatenating media files. Is this an extension issue? Anyway, not having the right container and codec will cause errors, so maybe a check is needed, if these settings are correct, and inform the user if they are not correct.