MP4 vs MOV vs WEBM vs MKV: Which Video Format Should You Use?
A video file has two separate parts: the container (MP4, MOV, WEBM, MKV — basically a box that holds everything) and the codec inside it (H.264, HEVC, VP9, AV1 — the actual compression algorithm). Most "which format is best" confusion comes from mixing these up: the container mostly affects compatibility, while the codec is what actually determines file size and quality.
Quick comparison
| Format | Best for | Trade-off |
|---|---|---|
| MP4 | Sharing, uploading, social platforms, messaging apps | The universal default — plays everywhere, no exotic features |
| MOV | Apple ecosystem editing (Final Cut, iMovie), ProRes workflows | Larger files, weaker support outside Apple devices |
| WEBM | Embedding video directly on a webpage | Smaller at the same quality (VP9/AV1), but less support in older apps and editors |
| MKV | Archiving, multiple audio/subtitle tracks in one file | Very flexible, but poor native support on phones, TVs, and social platforms |
The practical default: MP4 with H.264
If you only remember one thing from this guide: for anything you're sending to another person, uploading somewhere, or posting on social media, MP4 with H.264 video and AAC audio is the safest choice. It plays natively on virtually every phone, browser, smart TV, and social platform without conversion.
When the other formats actually make sense
MOV is what your iPhone or a professional camera records by default — keep it if you're editing further in Apple software, but convert to MP4 before sharing. WEBM is worth using specifically when you're embedding a video directly in a website's HTML, since browsers can stream it efficiently. MKV shows up mainly in archival or technical workflows where you need multiple audio tracks or subtitle streams bundled together — it's rarely the right choice for anything you plan to share casually.
FAQ
Does changing the container (without re-encoding) change file size?
Only slightly — remuxing (changing container without re-encoding) doesn't touch the actual video/audio data, so size stays nearly the same. Real size reduction requires re-encoding the codec inside, which is what compression does.
Is WEBM always smaller than MP4?
At the same visual quality, WEBM (VP9/AV1) can be somewhat smaller than MP4 (H.264), but MP4 with H.264 remains far more universally supported across social platforms, older devices, and messaging apps.
Why do some MKV files not play on my phone or TV?
MKV is a flexible container that can hold almost any codec, including ones your device's hardware decoder doesn't support — converting to MP4 with H.264 guarantees playback almost everywhere.
Shrynk reads MP4, MOV, MKV, AVI and WEBM as input, and always outputs a universally compatible MP4 — no separate "convert" step needed. Need to batch-convert a whole folder? The Shrynk desktop app does that too, for a one-time $9.