MP4 vs MOV vs MKV vs WebM: Video Container Formats Explained

MP4 (MPEG-4 Part 14) is based on the ISO base media file format, which itself grew out of Apple's QuickTime format. It is the default for phones, social networks, video platforms and web browsers. It typically carries H.264 or H.265 video with AAC audio, and it can also hold AV1 and VP9.

MP4 handles multiple audio tracks and chapters, but its subtitle support is limited: the standard text format (often called mov_text) is supported by fewer players than the SRT or ASS subtitles common in MKV files. When compatibility is the goal, MP4 is almost always the right answer.

MOV is Apple's QuickTime container and the format iPhones and Macs write by default. Structurally it is very close to MP4, which is why converting between the two is usually quick and lossless when the codecs are compatible. MOV is common in professional workflows because it can carry editing-friendly codecs such as Apple ProRes.

On Apple devices MOV is first class. On Windows and Android most modern players open it, but some web uploaders and older software expect MP4. If a MOV file is being rejected, converting it with MOV to MP4 is the usual fix.

MKV (Matroska) is an open, royalty-free container that can hold almost any codec: H.264, HEVC, VP9, AV1, AAC, Opus, FLAC, AC-3, DTS and more. It supports any number of audio and subtitle tracks, rich subtitle formats such as ASS and image-based PGS, chapters and attachments like fonts. That makes it popular for archiving and for films with several languages.

Its weakness is device support. Apple's built-in players, many web browsers and some TVs do not play MKV at all, or play the video but not the audio or subtitles. Our guide on why MKV files won't play covers the fixes in detail.

WebM is a restricted version of Matroska designed for browsers. It only allows royalty-free codecs: VP8, VP9 or AV1 for video and Vorbis or Opus for audio. That restriction is the point, because it means any browser that supports WebM can play any valid WebM file without licensing questions.

WebM is a good choice for video embedded on web pages and for screen recordings made in the browser. It is a poor choice for sending to someone who will open it in a desktop video editor or an older phone, where MP4 is safer. The WebM to MP4 page converts in one step.

These are general tendencies rather than guarantees; the codecs inside matter as much as the container.

• Best compatibility: MP4, then MOV. MKV and WebM depend on the player.
• Most codec freedom: MKV. WebM is deliberately the most restricted.
• Subtitles: MKV supports the widest range of formats; MP4 and MOV support simpler text subtitles.
• Editing: MOV and MP4 import cleanly into most editors; MKV support varies.
• Web embedding: MP4 with H.264 plays everywhere; WebM with VP9 is a good royalty-free option.

Because the container is only the box, it is sometimes possible to move the streams into a different box without touching the compressed video. This is called remuxing or stream copy. It is fast and loses nothing, but it only works if the destination container supports the codecs: H.264 and AAC move from MKV to MP4 without problems, but VP9 cannot go into MOV and a DTS audio track is a poor fit for MP4.

When the codecs are not compatible, or when you want a different codec, resolution or bitrate, the video must be re-encoded. Re-encoding takes longer and, with lossy codecs, loses a little quality each time, which is why it is best to convert from the original file rather than a copy of a copy.

The Video Converter page opens on the AI assistant, which makes MP4, MOV, MKV and WebM and takes a resolution, frame rate or bitrate in your request, but not a codec. Its classic converter, one click away on the page, writes MP4, MOV, MKV, WebM, AVI, FLV and TS, and when you pick an output format it only offers codecs that container can hold, so you cannot accidentally produce an invalid combination. For MP4, MOV, MKV and WebM output it re-encodes the video as part of the conversion, which is also what lets you change the codec, resolution or bitrate at the same time; leave those at their defaults, which follow the source, to stay close to the original quality. For AVI, FLV and TS output, an H.264 picture is carried across without re-encoding when you keep the default settings, unless it comes from an AVI going into another format: an AVI keeps only decode-order frame times, so its video is re-encoded. Everything runs in your browser, so the file is not uploaded anywhere. For the most common jobs there are pages with the output already selected, including MKV to MP4, MOV to MP4 and MP4 to WebM.