Container versus codec
A codec compresses the picture or sound: H.264, H.265, VP9 and AV1 for video, AAC, MP3 and Opus for audio. A container stores those compressed streams together with timing, metadata, chapters and sometimes subtitles: MP4, MOV, WebM and MKV.
The same H.264 video can sit in an MP4, a MOV or an MKV. Moving it from one container to another is called remuxing. It copies the streams without re-encoding, so it is fast and loses nothing, as long as the new container accepts those codecs.
Video InfoSee exactly which codecs are inside a file before converting it.The four common containers
- MP4 is the default for sharing. It usually holds H.264 or H.265 video with AAC audio, and it plays on phones, browsers, TVs and every social app.
- MOV is Apple's QuickTime format and a close relative of MP4. iPhones record MOV files with H.264 or HEVC video. It is common in editing (including ProRes), less so for sharing on non-Apple devices.
- WebM is the web's open format, holding VP8, VP9 or AV1 video with Vorbis or Opus audio. It is used for web video and screen recordings made in the browser.
- MKV (Matroska) can hold almost any codec plus several audio and subtitle tracks. It is popular for films and series, but phones, TVs and browsers do not all play it.
Compatibility at a glance
| MP4 (H.264) | MOV | WebM | MKV | |
|---|---|---|---|---|
| iPhone and iPad | Yes | Yes | Limited | No (without an app) |
| Android | Yes | Usually | Yes | Often, depends on player |
| Windows | Yes | Usually | Yes | Yes, in most players |
| Chrome, Edge, Firefox | Yes | Partly | Yes | Partly |
| Safari | Yes | Yes | Recent versions | No |
| Instagram, TikTok, WhatsApp | Yes | Yes | Not reliably | No |
Support depends on the codec inside as well as the container. An MKV holding H.264 is easier to play than one holding an unusual codec, and an MP4 holding H.265 will not play everywhere an H.264 MP4 does.
Which one to use
- Sharing with anyone, uploading anywhere: MP4 with H.264 and AAC.
- Editing on a Mac or with Apple tools: MOV is fine, and converts to MP4 losslessly when the codecs allow.
- Embedding on a web page with a small file: WebM (VP9) alongside an MP4 fallback.
- Keeping several languages and subtitle tracks in one file: MKV.
Does converting lose quality?
Remuxing (MOV with H.264 to MP4, for example) loses nothing. Converting to a container that does not accept the original codec, such as MP4 to WebM, requires re-encoding, which costs a little quality and takes longer. Converting MKV to MP4 is usually a remux, but some MKV audio or subtitle formats have to be converted along the way.
Extract SubtitlesSave the subtitle tracks from an MKV before converting it, so none are lost.Questions
Is MP4 better quality than MOV?
Neither container has better quality. Quality depends on the codec and its settings. An H.264 stream looks the same in MP4 or MOV.
Why won't my MKV play on my phone?
Many phone and TV players do not support the MKV container or the codecs inside it. Converting to MP4 usually fixes it, often without re-encoding.
Can I convert WebM to MP4 without losing quality?
Usually not entirely. WebM holds VP8, VP9 or AV1, which most MP4 players expect as H.264, so the video is re-encoded. Choose a high quality setting to keep the loss small.
What does remux mean?
Copying the existing video and audio streams into a different container without re-encoding them. It is fast and lossless when the new container supports the codecs.
Which format is smallest?
Size depends on the codec, not the container. VP9 in WebM and H.265 in MP4 are usually smaller than H.264 at the same quality.