itag is the most efficient way to talk about a YouTube format. Instead of "1080p H.264 video-only stream in MP4", you say "itag 137" and anyone who has seen the YouTube format table knows exactly what you mean.
There are around 100 itags in active use, give or take. Most have been stable for years. A few useful ones:
- 18: 360p progressive (H.264 + AAC in MP4) — universal compatibility, always available. - 22: 720p progressive (H.264 + AAC in MP4) — was the default download for years. - 137: 1080p video-only (H.264 in MP4). Needs muxing with separate audio. - 136: 720p video-only (H.264). - 140: 128 kbps AAC audio in m4a. - 141: 256 kbps AAC audio (rare, premium content). - 160: 144p video-only. - 248 / 303: 1080p VP9 (smaller than H.264 equivalent). - 271: 1440p VP9. - 313 / 315: 4K (2160p) VP9 / VP9-HFR. - 401: 4K AV1 (smaller than VP9 equivalent). - 571: 8K (4320p) AV1.
Downloaders that say "this is what you're downloading" technically can be more precise than the human-readable version. The flip side: when a tool says "itag 137 unavailable" it means "1080p H.264 isn't served for this video" — usually because the uploader didn't include that format.
Common questions
Why does YouTube use itags instead of "1080p"?
Is itag the same as a YouTube format code in yt-dlp?
Related terms
Codec
A codec is the algorithm that encodes (compresses) and decodes raw audio or video into a smaller stream.
Container (file format)
A container is the file format that wraps one or more audio and video streams into a single file.
Bitrate
Bitrate is the amount of data a video or audio stream carries per second, measured in bits per second (bps) or kilobits (kbps) and megabits (Mbps).
Manifest (streaming)
A manifest is a small text file that lists every segment of a streaming video, plus available qualities, codecs, and timing.
VidPickr is a free, browser-based YouTube downloader. Every term in this glossary either describes how YouTube delivers video or why your downloads behave the way they do. Try the downloader →