When analyzing YouTube video streams using data tools like "Stats for Nerds" or downloading media via command-line utilities like yt-dlp , you will encounter highly specific technical strings in the format metadata. Two of the most common and optimal identifiers appearing in modern high-definition streams are the video codec string av01.0.08M.08.399 and the audio codec string opus (251) .
If you paste codecs av01008m08 399 opus 251 new directly into VLC, MPC-HC, or FFmpeg, you will get errors. Here’s why:
AV1 codec strings follow a strict pattern defined by the AV1 Codec ISO Media File Format Binding (AV1-ISOBMFF v1.2.0). Correct format: av01.N.xxM.yy
: This is an internal format identifier known as an ITAG value . YouTube uses ITAG 399 specifically to request and track a 1080p resolution AV1 video stream encoded at a highly compressed, efficient bitrate. 2. The Audio Track: opus (251) This segment details the accompanying audio stream:
: Refers to Profile 0 (Main), which supports 8-bit or 10-bit color.
Based on standard YouTube format lists, itag 399 corresponds to a specific stream profile: a . The full command output from the youtube-dl tool confirms this, showing it as a video only stream, meaning it doesn't contain audio.
Without more specific information on these codes and configurations, it's challenging to provide a detailed analysis. However, understanding the role of codecs like Opus and the importance of configuration settings is crucial for optimizing media for various applications.
Are you looking to streams using these specific formats?
: This is a YouTube-specific itag (internal format ID) that typically corresponds to 1080p resolution AV1 video. The Audio Standard: Opus (251) Difference between 251 Opus and 141 mp4a? : r/YoutubeMusic