MP4 is the safest default
MP4 is usually the safest video format for social platforms, browsers, phones, school portals, and generic upload forms.
When to convert to MP4
Convert MOV, AVI, MKV, WMV, FLV, 3GP, or MPG to MP4 when a video will not upload, preview, or play on the destination platform.
After conversion
Check duration, audio sync, orientation, captions, and aspect ratio before deleting the original video.