399 Mp4 May 2026

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

According to technical discussions on Reddit and GitHub , 399 is often preferred because: 399 mp4

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 (In this example, 399 is the 1080p AV1

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 Copied to clipboard It is the most modern

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

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