Mp4 | 399

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

Format is a video-only stream used by YouTube for high-quality content. Key characteristics include: Resolution: 1080p (Full HD). 399 mp4

According to technical discussions on Reddit and GitHub , 399 is often preferred because: It is the most modern codec YouTube offers

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

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

Supports up to 60fps (High Frame Rate/HFR), offering smoother playback for action-heavy content.

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