Convert MOV to MKV

Only the wrapper changes

A video file separates into two things: the encoded picture and sound, and the container describing how they sit together. Remuxing changes the second and leaves the first exactly as it was.

A MOV from an iPhone or a Mac screen recording almost always holds H.264 video and AAC audio. MKV carries both without complaint. So the streams can be lifted out of Apple's structure and written into Matroska's with nothing decoded, nothing encoded, and nothing lost.

How it works

-c copy tells ffmpeg to copy every stream rather than process it. No frame is examined and no encoder runs. The MKV that comes out holds the identical video and audio data.

Because there is no encoding, the time taken is bounded by reading and writing rather than by how much video there is. A long recording remuxes about as quickly as a short one.

Why leave the Apple container

MOV is not a bad format — it is the ancestor of MP4 and technically capable. The reasons to move are practical.

Media servers handle MKV better. Plex, Jellyfin and Kodi read it natively, index its tracks properly and expose subtitles and alternative audio as things a viewer can switch between. MOV works, less consistently, and with more variation between clients.

Subtitles are the sharper case. MKV holds them as selectable text, several at once. If you are captioning something, doing it in MKV means the viewer can turn captions on and off. Doing it in a container that handles them poorly usually ends with the text burned into the picture, which is permanent and cannot be translated later.

What you give up

Reach. MOV opens on every Apple device and in most desktop software. MKV plays in VLC, MPV, the media servers and many televisions, and not in browsers, not on most phones, and not on older hardware.

Since remuxing costs nothing and takes seconds, keeping both is the obvious arrangement: the MOV for anything Apple or anything you are sending to a person, the MKV for a library or a server.

When a remux fails and a conversion would not

Very occasionally a MOV holds something MKV has no defined way to store — usually a stream from professional editing software, such as a timecode track or an uncommon audio layout. Copying cannot invent a place to put it, so the remux stops rather than silently dropping it.

That is the correct behavior and it is worth recognizing when you see it. The fallback is to convert to MP4 instead, which re-encodes and will accept the file, at the usual small cost in quality. A failure here is information about the source, not a fault in the conversion.