MP4 vs MKV — which should you keep?

They both hold the same films and often the same codecs, so the difference is not quality. It is what each one is allowed to carry.

MP4 travels well

MP4 compatibility depends on the codecs inside it and the target device.

MKV carries more

MKV can hold several audio and subtitle tracks, chapter marks and additional metadata. Support for individual track formats depends on the player. That flexibility is why film collections and disc rips often use it.

Which to keep

For an archive, compare the actual tracks in each copy before choosing what to keep. If a file has to play on unknown hardware, MP4 is the safer bet. With AIX Player the question is largely moot, because both open the same way and both cast to the television.

Converting between them is usually pointless

Changing containers can be useful for a target device; a remux can copy the video without re-encoding it. If the video inside is already something the destination can read, the conversion changes only the box. If the target needs another video codec, a lossy re-encode can reduce quality. Playing the file as it is avoids both outcomes.

Which one to keep when you have both

Compare the actual audio, subtitle and chapter tracks in each file, and keep the copy you need. Neither the extension nor file size proves completeness or casting compatibility.

What about the other containers?

MOV, MP4 and AVI are distinct containers; playback depends on their contents. TS and M2TS come off discs and broadcasts, and hold exactly what was transmitted. WebM is the browser format. All of them open in AIX Player, so the container matters far less than what is inside it.

Worth knowing