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 is the safe choice. Almost every device, browser and television reads it, which is why phones record in it and why it is the format to keep if a file needs to work everywhere without thought.

MKV carries more

MKV can hold things MP4 cannot: several audio tracks, unlimited subtitle tracks in any format, chapter marks and disc-style menus. That is why film collections and disc rips use it — one file holds every language and every subtitle.

Which to keep

If you archive films, keep MKV: nothing is thrown away. 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

People convert MKV to MP4 constantly, and most of the time it achieves nothing but a long wait and a slightly worse picture. If the video inside is already something the destination can read, the conversion changes only the box. If it is not, the conversion has to re-encode the picture, which always loses a little quality. Playing the file as it is avoids both outcomes.

Which one to keep when you have both

Keep the MKV. It carries every audio track, every subtitle language and the chapter marks, and you can always play or cast it without converting. The MP4 version is the compromise copy — useful if a file has to work on unknown hardware, and worth deleting otherwise, since it is usually the same film with things removed.

What about the other containers?

MOV is essentially MP4 with an Apple heritage and behaves the same way. AVI is far older and cannot carry modern video properly. 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