AV1 is a new video coding format. It achieves better compression than H264, similar compression to H265 and unlike H265, has an uncomplicated licensing scheme and is royalty free. There is a sister format for images called AVIF. You will be seeing more of these files on the web as time goes on.

If you got here because a video wouldn't play, it's probably because macOS and iOS do not support AV1. This is Apple's fault, not mine. There is no legitimate reason that Apple cannot or should not support AV1; they simply chose not to. If you are a macOS or iOS user (as I am), I encourage you to bring this to Apple's attention.

If you're on Windows and it doesn't play, try this.

You are probably wondering, why not use H264 since everyone can play it? That's because H264 is restrictively licensed and collects royalties, and AV1 does not. I apologize for the inconvenience, but it is a way of driving AV1 adoption, which ultimately serves the greater good. Thank you for your sacrifice.