H.264, VP9, and AV1 Video Codecs: Which to Choose and Why It Matters

A codec decides how the video gets compressed. H.264 is the most compatible: it plays everywhere, though it compresses less efficiently. VP9 and AV1 are more modern and efficient (same quality, less size), but not every device can play them. Quick rule: if you want the video to work anywhere, look for H.264 (usually inside MP4); if you prioritize smaller size and you'll watch it on modern devices, go with VP9 or AV1.

What Is a Video Codec?

Don't confuse codec and format. The format or container (MP4, WebM, MKV) is the box that wraps the video; the codec is the technique used to compress and decompress that video inside the box. The same MP4 file can carry H.264 or AV1 inside. The codec affects two things: how much space the file takes up and which devices can play it without issues. For the difference between containers, see MP4 vs WebM.

H.264, VP9, and AV1 Compared

Compatibility Versus Efficiency

The underlying tension is always the same: the newer and more efficient a codec is, the fewer devices can play it. H.264 is over fifteen years old and even the oldest phone or TV understands it, but it compresses less efficiently, so its files take up more space. AV1, at the other extreme, offers the best quality per megabyte, but only recent devices play it smoothly. VP9 sits in between: fairly efficient and already well supported.

Which Codec Does YouTube Use?

YouTube encodes each video in several codecs at once and serves whichever best fits your device and connection. In practice you'll see H.264 at many resolutions (for its compatibility), VP9 across much of the catalog, and AV1 mainly in 4K and recent uploads. That's why, when downloading, the same video can be offered in different codecs depending on the resolution.

Why It Matters When Downloading

• Compatibility: if the video is going to an older phone, a TV, or an editor, H.264 (in MP4) is the safest bet.
• Size: to save space at the same quality, VP9 or AV1 perform better, especially at higher resolutions.
• 4K: a lot of 4K content uses VP9 or AV1, which the MP4 container doesn't always support copying the track as-is; that's why 4K sometimes arrives in WebM or MKV.
• Editing: editors prefer H.264; if you're going to edit, avoid AV1 unless your software supports it well.

So, Which Do I Choose?

If you don't want to overthink it, download in MP4 with H.264: it works everywhere. If size matters to you and you'll watch the video on a modern device, VP9 or AV1 give you the same quality at a smaller size. And if you download in 4K from YouTube, it's normal to run into VP9 or AV1, because those are the codecs used to distribute high resolution. To decide on the resolution itself, see what resolution to download.