MP4 vs MOV vs MKV vs AVI vs WebM: What Is the Difference?
People often treat MP4, MOV, MKV, AVI and WebM as if they were different quality levels. They are not. They are containers: a kind of box that holds a video stream, one or more audio streams, and sometimes subtitles and metadata. What matters for quality and file size is mostly the codec inside the box.
Container vs codec in one minute
- A codec (for example H.264, VP8, AAC, MP3) is the method used to compress the picture or the sound.
- A container (for example MP4, MKV) is the file format that packages those compressed streams together.
The same H.264 video can be placed in an MP4, a MOV or an MKV file. Changing only the container is quick and lossless when done by "copying" the streams; changing the codec means re-encoding, which takes longer and can reduce quality slightly. Free Video Converter always re-encodes, so keep that in mind.
The five formats
| Format | What it is | Strengths | Weaknesses |
|---|---|---|---|
| MP4 | An international-standard container, usually holding H.264 video and AAC audio. | Plays on nearly everything: phones, browsers, TVs, editors. | Less flexible than MKV for many tracks and subtitle types. |
| MOV | Apple's QuickTime container. MP4 is closely related to it. | Native to Apple devices and apps; common in video editing workflows. | Some non-Apple players and devices handle it less smoothly. |
| MKV | The open Matroska container. | Holds many audio, subtitle and chapter tracks; popular for archives and downloaded video. | Not supported by default in as many TVs, phones and editors as MP4. |
| AVI | An old container from Microsoft, introduced in the early 1990s. | Very old players and software can open it. | Dated design; large files for the quality; poor fit for modern codecs and streaming. |
| WebM | A web-focused format derived from Matroska, designed for the open VP8, VP9 and AV1 video codecs. | Built for the web and open, royalty-free codecs. | Device and software support is narrower than MP4. |
What this site produces for each
| Output | Video | Audio |
|---|---|---|
| MP4 | H.264 | AAC, 128 kbps |
| MOV | H.264 | AAC, 128 kbps |
| MKV | H.264 | AAC, 128 kbps |
| WebM | VP8 | Vorbis |
| AVI | MPEG-4 Part 2 | MP3, 128 kbps |
Because MP4, MOV and MKV outputs here all use the same H.264 and AAC settings, they will look and sound essentially the same; only the wrapper differs. Choose between them based on where the file has to play, not on expected quality.
Which should you choose?
- You want it to just work: MP4. See how to convert a video to MP4.
- You are working with Apple software: MOV is fine, though most Apple apps also open MP4.
- You are keeping a file with several audio or subtitle tracks: MKV is the better container in general. Note that this site keeps one video and one audio stream, so for multi-track files a desktop tool is a better fit.
- You are embedding video on your own web page: MP4 is the safest; WebM is a reasonable extra. Read when to use WebM.
- You have an old player or device that only understands AVI: use AVI, otherwise avoid it.
A common misunderstanding
Renaming a file from .mkv to .mp4 does not convert it. The extension is only a label; the contents are unchanged, and many players will refuse to open the file or show errors. To change the format properly you need a real conversion.
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