MP4 vs WebM: Which Video Format Should You Choose?

When you download from YouTube you are often offered the same video twice, once as MP4 and once as WebM, sometimes at different resolutions. Most people pick whichever is higher and then wonder why the file will not open on their TV, or why it has no sound.

The choice is not arbitrary and it is not about quality in the way people assume. Here is what actually separates them.

Containers and codecs, briefly

MP4 and WebM are containers. A container is a box: it holds a video stream, an audio stream, and metadata like subtitles and chapters. It does not itself determine quality.

What is inside the box is the codec, and that is what does the compressing. A file named clip.mp4 tells you about the box, not the contents. Two MP4 files can hold completely different codecs, which is why one plays on an old TV and the other shows a black screen with working audio.

• MP4 almost always contains H.264 video and AAC audio. This combination has been the web standard for well over a decade.
• WebM contains VP9 or AV1 video and Opus audio. All three are open, royalty free formats developed largely by Google.
• Newer MP4 files sometimes contain H.265, also called HEVC, which is more efficient but patent encumbered and less universally supported.

The efficiency argument, with numbers

VP9 compresses roughly 30 to 50 percent better than H.264 at the same visual quality. AV1 does better still, roughly 30 percent beyond VP9, at the cost of much heavier decoding.

In practice that means a ten minute 1080p video might be 150 MB as H.264 in MP4 and around 90 MB as VP9 in WebM, and they will look about the same. If storage or bandwidth is your constraint, WebM wins clearly.

This is exactly why YouTube serves WebM by default in browsers that support it. At YouTube's scale, a third off the bandwidth bill is an enormous number.

The compatibility argument, which usually wins

H.264 has dedicated decoding hardware in essentially every phone, laptop, tablet, games console and television made in roughly the last fifteen years. VP9 support is good on modern devices and patchy on older ones. AV1 hardware decoding only became common around 2021.

Concretely, here is where WebM causes trouble:

• Smart TVs, particularly anything more than a few years old, frequently refuse it outright.
• iPhones and iPads play WebM in Safari but will not import it into Photos, so it stays stuck in Files.
• Premiere Pro does not import WebM without a plugin. Final Cut does not either.
• Most social platforms reject WebM on upload, so you would have to convert before posting.
• Older Android devices fall back to software decoding, which drains battery and stutters on high resolutions.

Software decoding is the hidden cost. A device without hardware VP9 support will still play the file, using the CPU, which on a phone means heat and a visibly shorter battery life on a long video.

The silent file problem

This catches more people than any compatibility issue. Above 1080p, YouTube does not store video and audio together. It keeps them as separate streams and the player combines them on the fly while you watch.

Download a 1440p or 2160p option without a muxing step and you get the video stream on its own, which is silent by definition. Nothing is broken and no audio was lost. It is simply in a different file.

Two fixes. Take the 1080p option, which is usually stored combined and comes with sound. Or merge the streams yourself: ffmpeg -i video.webm -i audio.m4a -c copy output.mkv takes a couple of seconds and does not re-encode anything. Our piece on why downloaded videos have no sound covers this and the three other causes of silence.

So which should you download

Pick MP4 when

• You are watching on a TV, a console, or any device you did not buy recently.
• You are importing into a video editor.
• You are re-uploading to any social platform.
• You are on iPhone and want the file in your camera roll rather than stuck in Files.
• You are sending it to someone else and cannot control what they will open it with.

Pick WebM when

• You are archiving a lot of video and storage matters more than convenience.
• You only ever watch on a modern computer or phone, in a browser.
• You want the highest resolution YouTube offers, since 1440p and above are often WebM only.
• You are comfortable converting later if a compatibility problem comes up.

For most people, most of the time, MP4 is the right answer. WebM is the better format on paper and the worse one in a living room.

What each platform actually serves

YouTube is the only one of the five where this choice comes up regularly. It offers both containers across a wide range of resolutions, and its higher tiers are frequently WebM only. The YouTube downloader lists what exists for a given video rather than guessing on your behalf.

X, Instagram, TikTok and Facebook all serve MP4 with H.264 and AAC almost exclusively. There is no decision to make on those platforms because there is only one format on offer. Our guide to video formats for social media covers the containers, codecs and bitrates each platform uses on the way in.

How to tell what is actually inside a file

If you have a file and no idea what it holds, ffprobe answers in one line: ffprobe yourfile.mp4 prints the container, the video codec, the audio codec, the resolution and the bitrate. VLC shows the same information under Tools then Codec Information, which is easier if you would rather not use a terminal.

This is worth doing once on any file that misbehaves, because it turns a vague compatibility problem into a specific one. A television refusing to play a file tells you nothing useful. Knowing the file is VP9 inside WebM tells you exactly which download to take instead.

A note on file extensions and lying

Renaming a .webm file to .mp4 does not convert anything. The container is a structure inside the file, not a label on the end of its name. A player that opens the renamed file will read the actual contents, find WebM structure where it expected MP4, and fail, usually with a confusing error. Conversion requires an actual tool such as ffmpeg or HandBrake.