not supported format, and yet it is mp4

[joepareti54]

I thought mp4 is mp4 regardless, but on some devices the OBS output file is nt readable. Why?

 

[Suslik V]

Devices usually uses hardware acceleration (special chips), so they are limited to what they have on board. Different compression that may apply to media files targeted at different devices (top-level capable of what low-end even didn't know). The mp4 is supported on many platforms but inside they are all different. Main restrictions set by Color Space/Subsampling and encoding Level/Profile (internal restriction of the resolution, fps, bitrate, buffer size etc.) that is supported by the device.

 

[FerretBomb]

MP4 is a container format.
The video/audio datastreams inside can use a number of different CODECs, some of which may not be supported by every device.