IME it does accept MP4, just not every variation and profile.
It seems to only be a problem on Linux. The paid version supports MP4(H.264), but not AAC.
Well to be fair, Premiere Pro doesn't support MP4 on Linux either. :-)
I'm a very casual user, but I've only used it with mp4 files straight from my phone camera and Youtube downloads.
Doesn't accept my gopro videos for sure so it was useless to me when I tried it.
just use ffmpeg to remux the file?
every time you recompress a file you lose quality
Hence the use of the word "remux", it's lossless (no re-encoding).
It doesn't support H.264 or AAC. Just changing the container.
-vcodec copy -acodec copy
mp4 files usually contain H.264 encoded video which requires the paid version for audio it usually contains AAC encdoded audio which is not supported at all. You can't get away with just copying.