MP4, MOV, MKV, WebM — what's actually different
Almost all confusion about video formats comes from conflating two things: the container and the codec.
The container is a box; the codec is the compression
- Containers (MP4, MOV, MKV, AVI, WebM) hold a video track, audio tracks, subtitles and chapters in one file.
- Codecs (H.264, H.265, VP9, AV1, AAC, Opus) determine how those tracks are compressed.
"It's an MP4" therefore tells you nothing about whether it will play. An MP4 holding H.264 opens everywhere; an MP4 holding AV1 will not open on a five-year-old TV.
Which to use
| Container | Best for | Notes |
|---|---|---|
| MP4 | The default | The most widely supported: web, mobile, TV |
| MOV | Apple, editing | Carries editing codecs like ProRes |
| MKV | Archival, many tracks | Best for multiple subtitle and audio tracks |
| WebM | The web | Royalty-free; VP9/AV1 with Opus |
| AVI | Legacy files | Little reason to create new ones |
Changing the box without re-encoding
If an MKV holds H.264 video and AAC audio, converting it to MP4 needs no re-compression at all. You lift the tracks out and set them down in a new container. This is called remuxing.
Two things follow: quality is bit-for-bit identical, and an hour-long file finishes in seconds rather than the several minutes a re-encode would take — while also shaving a little quality.
OmniDesk detects when a conversion is only a container change and remuxes.
Extracting audio
Pulling an MP3 out of an MP4 is common. But a video with no audio track obviously yields nothing — screen recordings and silent clips fall into this trap.
Failing silently leaves people guessing. OmniDesk inspects the streams first and says plainly that the video has no audio track.
Converting to GIF
Turning video into GIF often makes the file bigger. GIF is limited to 256 colours and compresses poorly between frames.
- Don't GIF anything over ten seconds; trim first.
- Dropping to 10–15 frames per second usually halves the size.
- 480px wide is enough for most uses.
- If you only need a moving image, WebP or a short muted MP4 is far better.