make tuneskit same as handbrake conversion

[Happyhiker]

Bit obscure, hoping someone can help
I have ripped all my blurays to MP4 via makemkv, then handbrake. All work flawlessly on Plex.
I want to do the same with iTunes Purchases. So I've downloaded them, converted to MP4 using tuneskit drm stripper.

I get an MP4 but it wont play properly on plex.(plays ok on pc)

I can convert tuneskit mp4 via handbrake and it does work, but thats a double encode and takes ages.
Is there a way I can remux the tuneskit mp4 to be the exact same as a Handbrake mp without reencoding and lossing quality ( and quickly).

The bluray rips are of a high Mbs than tuneskit, so I dont really know why tuneskit doesnt work on plex, its not a bigger file. And I'm not transcoding plex.

Anyone any ideas ?

[jagabo]

Try a simple remux with ffmpeg.

ffmpeg -i "source.mp4" -vcodec copy -acodec copy "output.mp4"