Tools like MKVToolNix often wrap MP4s into MKV to edit without re-encoding.

If you have access to the file, I recommend running these tools to see the "deep features" for yourself:

A true MKV file must start with the EBML header 1A 45 DF A3 . If the file fails to play, checking this header confirms if it's a genuine MKV or just a renamed MP4. 3. Practical Deep Inspection Steps

MKV files can store rich metadata that MP4s cannot, such as "Writing Application" (e.g., mkvmerge v70.0.0 ) or "Writing Library" (e.g., libebml ). This reveals which software handled the file after it left the phone.

Right-click the file to see the exact bitrate, encoding profile (e.g., Main@L4 ), and whether the "Encoded date" matches the filename date.