mkv to mp4 - Best conversion method?


New Member

If I record video in mkv format what is the best method or software for converting it to mp4?



Active Member
OBS does that itself. File -> Remux Recordings

It doesn't change the formatting at all. It's still h.264 video with aac audio, or whatever you've set it for, just in a different bucket with a different file extension. It's more to satisfy a stupid format checker than anything else, but if that's what it takes to make it work somewhere, then that's what it takes. And because it's not actually changing anything - just a bit-for-bit copy - it goes pretty fast, limited by the hard drive transfer rate, not the CPU.

The reason to record in MKV has nothing to do with the actual format, but the header structure that surrounds it. MP4 video is kinda like WAV audio in that the header can't be finished until the data is finished, so if the recording is interrupted without allowing it to tidy up, the header is bad and you can't access the data very well. MKV's headers work differently, and don't need to be "fixed up" after the recording finishes. Interrupt that, and the data is still easily accessible.
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Active Member
The easiest and best method for mkv videos you're creating with OBS is to activate OBS Settings->Advanced->Recording->Automatically remux to mp4. This way OBS will automatically remux an mkv to mp4 as soon as you stop the recording. It's doing automatically what you can do manually with File->remux recordings.

About the process in general: There is "recoding" and there is "remuxing". "Recoding" is slow and you lose quality during the conversion, because the software that does recoding unpacks the encoded video, then encodes it again with the new format. The re-encoding is what it will make lose quality. It's as if you're opening an envelope with a letter, then read and copy the letter by hand to a new letter, then put the copied letter into a new envelope. It's a new letter with a new envelope, you lose the paper, original handwriting and signature, and in addition you get typos from transcribing.

"Remuxing" is fast and doesn't lose a single bit of quality. It takes the encoded video data verbatim and just writes a new envelope for the video data. The mkv format is one envelope type, and the mp4 format is a different envelope type. It takes the encoded video out of the mkv envelope and directly put it into the mp4 envelope. It's like taking the letter out of its envelope and put the same letter into a new envelope. It's the same letter with a new envelope. You get a new envelope, but the original paper, handwriting and signature is preserved.