MP4, WebM or MKV: Which Format Should You Pick?

If you are unsure, choose MP4 and stop reading. For everyone else, here is what the choice actually changes.

Container versus codec

MP4, WebM and MKV are containers — boxes that hold a video track, an audio track and sometimes subtitles. The codec inside (H.264, VP9, AV1) is what determines how the picture is compressed. Two MP4 files can contain completely different codecs and behave very differently.

MP4

The default answer. It plays on every phone, every smart TV, every browser and every video editor without conversion. It usually carries H.264, which is old enough that hardware decoding is universal — meaning smooth playback and less battery drain.

Choose MP4 unless you have a specific reason not to.

WebM

Built for the web and usually carrying VP9 or AV1. At the same visual quality it is often noticeably smaller than MP4, which is why platforms serve it to browsers.

The catch is outside the browser: older TVs, some phones and several editors will not open it. It is a good choice if the file is only ever going to be watched on a computer, and a poor one if you plan to send it to someone else.

MKV

The most flexible of the three. It can hold multiple audio tracks, multiple subtitle tracks and almost any codec. That makes it the format of choice for films with alternate languages.

It is the least portable, though. Most phones will not play it without a third-party app, and uploading an MKV to a social platform almost always triggers a re-encode.

Quick guide

• Sending it to someone, or watching on a TV or phone? MP4.
• Storing a lot of video on a computer and tight on space? WebM.
• Keeping subtitles or several audio tracks? MKV.
• Importing into an editor? MP4, every time.

Converting later

Changing container afterwards is possible but re-encodes the video and loses a little quality each time. It is always better to download the right format once than to convert twice.