Mp4: 399

AV1 ( av01 ), which is a modern, royalty-free codec designed for better compression and quality compared to older formats.

(In this example, 399 is the 1080p AV1 video and 140 is the standard M4A audio stream.) Why Choose 399? 399 mp4

Supports up to 60fps (High Frame Rate/HFR), offering smoother playback for action-heavy content. AV1 ( av01 ), which is a modern,

It is the most modern codec YouTube offers for 1080p, allowing for higher frame rates that older caps (like 30fps) don't support. It is the most modern codec YouTube offers

Usually wrapped in an MP4 container, though it is technically "video-only" and must be merged with an audio stream (like itag 140) to create a playable video file. How to use it in yt-dlp

If you want to manually select this format to ensure you get the AV1 1080p version, you would use a command similar to this in your terminal: yt-dlp -f 399+140 [VIDEO_URL] Use code with caution. Copied to clipboard