Convert MOV to MKV

This is what separates this conversion from the same job starting at an MP4. Nobody sets out to collect QuickTime files: a Canon or Sony body writes MOV onto the card, a Blackmagic writes MOV, an iPhone writes MOV, Final Cut exports MOV. The format arrives with the equipment, and it arrives attached to Apple’s idea of how video should be packaged.

That is tolerable while everything downstream is a Mac and awkward the moment something is not. A Jellyfin server on Linux, a Kodi box under a television, a NAS with a transcoding plug-in and a folder full of scripts all handle Matroska as their native case and QuickTime as an import. Standardising the shelf on one open container is a real decision, and it is the one this page is written for.

The MP4 to MKV page argues the other way, and the argument is sound there: two containers holding the same ordinary H.264 stream should be joined with MKVToolNix in seconds rather than re-encoded. Nothing about that is wrong. It just does not apply to a file that came off a camera.

A remux is faithful, and faithfulness is the problem. Copying a ProRes stream, a 10-bit HEVC stream or a 4:2:2 H.264 stream into an MKV produces a perfectly valid file that the media box still refuses, because the codec was always what it was refusing. This conversion decodes and re-encodes to H.264 at High profile with AAC audio, which is the pair that plays on the hardware decoder of essentially anything. The generation of quality that costs is the price of the file being playable at all.

A phone shoots landscape and writes a flag saying how far to turn the picture. MP4 and MOV both carry that flag and both rely on the player reading it, which is why the same clip is upright in one application and on its side in another. Matroska does have a field for it — ProjectionPoseRoll — and enough players ignore the value that writing it would be a gamble.

So the conversion does the rotation for real: the frames are turned during the encode and the MKV holds an upright picture with no flag attached. It is slower than passing a number across, and it is the more durable result — a file that is upright in its pixels cannot be displayed sideways by software that never learned about rotation matrices. For footage going onto a server that will be read by several different clients, that is worth having.

MKV’s reputation rests on things this page cannot deliver. It will hold as many audio tracks as a release has any use for, soft subtitles you can switch on and off, chapter marks, attachments and several video streams side by side. It has been an open specification since 2002 with no vendor behind it, which is most of why it became the archival default.

What crosses over here is video and audio. Subtitle tracks, chapter marks and the timecode track a camera writes are not read at all, so an MKV made this way is a clean single-video, audio-bearing file rather than a fully furnished library object. If you want the furniture, MKVToolNix can add subtitle and chapter tracks to the MKV afterwards without touching a frame.

ProRes is the common one. It is what Final Cut Pro, an Atomos recorder and most cinema cameras write, and no browser exposes a ProRes decoder — so the conversion stops with a message saying that nothing in the file could be converted and that a codec may be missing. The same happens for anything else a professional workflow tucks into a QuickTime wrapper.

The message is deliberately about the decoder rather than the file, because the file is fine. Export an H.264 or HEVC version from whatever produced the ProRes and convert that, or do the whole job in a desktop encoder. A browser cannot conjure a codec the operating system does not have, and pretending otherwise would just move the failure to a less useful moment.

Because this is a re-encode, the quality band is not decoration. It resolves to a target bitrate scaled by resolution: at 1080p the three bands are roughly 1.8, 3 and 6 megabits a second, and at 4K roughly 6.7, 11.2 and 22.4. For a file that is going to be the copy you keep, the high band is worth its size, because everything you ever do with the footage afterwards will be made from it.

Resolution only goes down, and dropping 4K to 1080p is usually the better saving than lowering the quality band at the same size. It also removes work from the server: a media box that would have scaled every frame on every playback is instead handed a file at the resolution it was going to display anyway.

No browser plays Matroska and none is going to start, so anything you might want to link to, embed in a page or drop into a messaging app should be an MP4 instead. Apple’s own players refuse it too, which is worth knowing if the household has both a Linux server and an iPad.

Matroska is also not designed for progressive streaming the way MP4 is, so serving one over plain HTTP to a player that starts before the download finishes works badly. Inside a home network, with a server that transcodes on demand, none of that matters — and that is precisely the situation where converting a drawer of MOV files to MKV pays for itself.

It runs on your own processor, through the hardware encoder the operating system already exposes, so the time is proportional to the length and the resolution rather than to the size of the file. There is no queue and no upload, which on a hosted converter is normally the slowest part of the whole job by a wide margin.

The free ceiling is 100 MB per file. Camera originals pass that quickly — 4K at 30 frames a second from a phone is roughly 170 MB a minute — so this suits clips, takes and short pieces rather than a whole card. A library-scale conversion belongs in a desktop encoder that can be left running overnight.

The whole conversion happens in this tab, using the decoders and encoders your computer already has. Nothing carrying the video is sent anywhere, and the network tab will show you that while a file is converting.

For this pair the argument is practical before it is principled. The footage is yours, it is large, and the destination is a machine in the same room. Sending several hundred megabytes to somebody else’s server so that it can come back and be copied two metres was never the sensible route, and it is the one thing a browser-based converter genuinely improves on.