This "double extension" suggests the original MP4 file was re-wrapped into a Matroska (MKV) container. This often happens during:
If you have access to the file, I recommend running these tools to see the "deep features" for yourself: VID_20221215_105814_430.mp4.mkv
Likely a millisecond or sequence identifier used by the camera software to prevent naming collisions. This "double extension" suggests the original MP4 file
Tools like MKVToolNix often wrap MP4s into MKV to edit without re-encoding. VID_20221215_105814_430.mp4.mkv
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