MP4, WebM, MOV or MKV: Which Video Format Should You Use?

A video that won't play is almost never broken. Nine times out of ten it is packed in a format your player doesn't open. Learn two words, container and codec, and you can fix it yourself in a minute.

A container is the box, a codec is what's inside

Think of a video file as a lunch box.

• The container is the box. MP4, WebM, MOV and MKV are containers. The box holds a video track, one or more audio tracks and sometimes subtitles.
• The codec is how the food inside was packed. H.264, H.265, VP9 and AV1 are video codecs. AAC, Opus and MP3 are audio codecs.

A player needs to open both: the box and the packing. That is why two files that both end in .mp4 can behave differently. One holds H.264, which everything plays, and the other holds AV1, which older devices can't decode.

The four video formats you will meet

MP4

The safe choice. If you don't know what to pick, pick MP4. When a site offers the same quality as both MP4 and WebM, PasteAndSave gives you the MP4 copy for exactly that reason.

WebM

The format Google uses for much of YouTube. It often carries the highest qualities, such as 1440p and 4K, in a smaller file. It plays fine in browsers and on Android. The iPhone Photos app and some older TVs are less happy with it.

MOV

Apple's own format, and what an iPhone records. It plays on every Apple device and opens in every editing app. Outside Apple, use MP4 instead, since the same video in MP4 is far more widely supported.

MKV

A very flexible box that can hold almost anything, which is why films with several languages and subtitles often come as MKV. Most phones' built in players won't open it. VLC will.

Video codecs in plain words

• H.264: the oldest of the four and the most widely supported. Every phone, browser and TV made in the last ten years plays it.
• H.265, also called HEVC: about half the size of H.264 for the same look. iPhones record in it. Some Windows computers need an extra add on to play it.
• VP9: Google's codec, used across YouTube.
• AV1: the newest and most efficient, used more and more by YouTube and Netflix. Older phones and laptops may struggle to play it smoothly.

Audio formats: MP3, M4A and Opus

• MP3 plays on every device ever made. Pick it when you need the sound to work everywhere, including car stereos.
• M4A holds AAC audio, which sounds better than MP3 at the same size. Apple devices love it.
• Opus is the most efficient of all and is what YouTube streams. It hides inside WebM files, and you rarely meet it on its own.

On PasteAndSave, the M4A option keeps the original audio without converting it where the source allows, so nothing is lost. MP3 is converted at the bitrate you choose. The video to MP3 guide explains which bitrate to pick.

Which format should you download?

1. For a phone or for sharing: MP4.
2. For the sharpest YouTube copy on a computer: the highest quality on offer, even if it is WebM.
3. For editing: the highest quality on offer, in any format. Your editor will open it.
4. For music or a podcast: MP3 if it must play everywhere, M4A if you want the best sound for the size.

A file won't play? Try these, in order

• Install VLC. It is free on every phone and computer and plays nearly every format above.
• Check the ending of the file name. If it is not a video or audio format, such as .exe or .zip, delete it. That is not a video.
• Convert it with HandBrake. This free program turns any of these formats into a plain MP4 with H.264 that plays everywhere.
• Download again as MP4. If the source offers an MP4 version, that is the quickest fix of all.

Next lesson

You know how to pick a quality and a format. Lesson 4, Is It Legal to Download Videos?, covers what you are allowed to do with the file once you have it.