MP4 vs WebM vs MOV vs MKV — which video container should you pick?
Compare four video containers by the codecs they typically wrap (H.264 / H.265 / VP9 / AV1), browser support, and use case (delivery / editing / archive). Maps each to social, NLE, and web embedding.
Containers and codecs are different things — four axes
The first thing to get straight: MP4, WebM, MOV, and MKV are container formats, not codecs. A container is a wrapper that bundles a video stream, an audio stream, subtitles, and metadata into a single file. The video codec (H.264 / HEVC / VP9 / AV1) and audio codec (AAC / Opus / Vorbis) inside the container are a separate decision. That is why a .mp4 is not automatically H.264, and why the same AV1 stream can live inside an MP4 file or a WebM file.
Four axes drive the choice. Which codecs typically go inside decides playback compatibility in practice. Compatibility with social platforms, browsers, iOS, and Windows decides who can press play without trouble. Use case flips the optimum: delivery, editing, and archival pull in opposite directions. NLE support (Final Cut, Premiere, DaVinci Resolve, Avid) decides how much friction your editing workflow will have.
Side-by-side comparison
| Property | MP4 | WebM | MOV | MKV |
|---|---|---|---|---|
| Common video codecs | H.264 / HEVC / AV1 | VP9 / AV1 | H.264 / ProRes / HEVC | Almost anything (H.264 / HEVC / VP9 / AV1) |
| Common audio codecs | AAC / MP3 | Opus / Vorbis | AAC / PCM / ALAC | AAC / Opus / FLAC / AC3 |
| Licensing | Depends on codec (H.264 / HEVC via MPEG LA) | Royalty-free (VP9 / AV1 / Opus) | Depends on codec | Container itself is free |
| Social uploads | X / Instagram / TikTok / YouTube all accept | YouTube internal / web only | Re-encoded on upload | Rarely accepted (convert first) |
| Browser playback | Everywhere | Chrome / Firefox / modern Edge | Safari and a few others | Mostly unsupported (extensions only) |
| Multiple subtitle tracks | Limited (TX3G) | Limited | Limited | Strong (PGS / SRT / ASS, multilingual) |
| NLE support | Read by every major NLE | Limited (web-leaning) | Native in Final Cut / Premiere | Mixed |
| Year standardised | 2001 (ISO/IEC 14496-14) | 2010 (Google) | 1998 (Apple QuickTime) | 2002 (Matroska project) |
The “common codecs” rows describe what is paired together in practice, not what the specification permits. The MP4 spec was updated in 2018 to officially carry Opus, and MKV can carry H.264 just fine — but real-world playback compatibility is driven by the typical pairings, not the specs.
Use case → recommended container
Social posts (X, Instagram, TikTok, YouTube): MP4 with H.264 + AAC. The platform will re-encode anyway, but upload-time compatibility is most predictable here. You can upload HEVC or AV1 inside MP4, but the playback problem is pushed onto older devices that receive the original.
Self-hosted video on your own site: WebM (VP9 or AV1) as the first <source>, MP4 (H.264) as the fallback inside a <video> element. WebM often lands 30-50 % smaller at the same perceived quality, which directly improves bandwidth bills and page load time.
Editing in Final Cut Pro or Premiere Pro: MOV (ProRes or H.264). Apple’s QuickTime container has the deepest native support in professional NLEs. ProRes is the standard intermediate codec — it survives multiple edit passes without visible degradation.
Home server, NAS, multilingual movie archives: MKV. Multiple audio tracks and multiple subtitle formats (SRT / ASS / PGS) bundle into a single file, and the container is codec-agnostic. The right choice if your playback environment is VLC, mpv, or Plex; the wrong choice if iOS or Apple TV native apps need to play it.
Converting containers locally in the browser
Tasks like “I have a MOV with H.264 inside, I want an MP4” or “I want to repost this WebM to social as MP4” are handled by video-convert. It uses ffmpeg.wasm to transcode between MP4, WebM, MOV, MKV, and AVI, with output codec selection (H.264, VP9, and so on). There is no code path that ships your footage or work-in-progress to a server.
Worth knowing: remuxing and transcoding are not the same operation. Going MOV (H.264 + AAC) → MP4 (H.264 + AAC) is just repacking the same streams into a different container — zero quality loss. Going WebM (VP9) → MP4 (H.264) is a full re-encode, and chaining lossy codecs erodes quality each time. If all you want is a smaller file, video-compress lets you re-pick the bitrate inside the same container, which is safer than repeated transcoding. The source is auditable on GitHub, and the DevTools Network tab makes it straightforward to confirm the video never leaves the browser.