399 Mp4 -

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

It is the most modern codec YouTube offers for 1080p, allowing for higher frame rates that older caps (like 30fps) don't support. 399 mp4

It provides better visual quality at a lower bitrate than the older H.264 (AVC) codec. AV1 ( av01 ), which is a modern,

(In this example, 399 is the 1080p AV1 video and 140 is the standard M4A audio stream.) Why Choose 399? AV1 ( av01 )

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

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