According to technical discussions on Reddit and GitHub , 399 is often preferred because:
Supports up to 60fps (High Frame Rate/HFR), offering smoother playback for action-heavy content.
AV1 ( av01 ), which is a modern, royalty-free codec designed for better compression and quality compared to older formats. 399 mp4
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
It provides better visual quality at a lower bitrate than the older H.264 (AVC) codec. According to technical discussions on Reddit and GitHub
Format is a video-only stream used by YouTube for high-quality content. Key characteristics include: Resolution: 1080p (Full HD).
(In this example, 399 is the 1080p AV1 video and 140 is the standard M4A audio stream.) Why Choose 399? Copied to clipboard It provides better visual quality
It is the most modern codec YouTube offers for 1080p, allowing for higher frame rates that older caps (like 30fps) don't support.