Adaptive streaming solves the streaming-on-unreliable-networks problem. The same video is encoded at multiple quality variants (144p, 240p, 360p, 480p, 720p, 1080p, etc.), each chunked into ~5-second segments. The player's ABR algorithm watches the buffer and current download speed, then picks the appropriate quality for the next segment.
On a strong connection, the player escalates to higher quality. When bandwidth drops, it falls back. The user sees occasional quality shifts but rarely sees buffering, because the algorithm prefers degrading quality over draining the buffer.
For downloaders, adaptive streaming means the video isn't stored as a single file. There are many segment files per quality. Downloading "the video" means picking one quality and fetching all its segments — what kkdai and yt-dlp do internally, then muxing them with the matching audio segments.
Common questions
Is adaptive streaming the same as DASH?
Related terms
DASH (MPEG-DASH)
DASH (Dynamic Adaptive Streaming over HTTP) is an open streaming protocol.
HLS (HTTP Live Streaming)
HLS (HTTP Live Streaming) is a streaming protocol developed by Apple.
Manifest (streaming)
A manifest is a small text file that lists every segment of a streaming video, plus available qualities, codecs, and timing.
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).
Fragmented MP4
Fragmented MP4 (fMP4) is an MP4 variant where the file is split into many short chunks ("fragments"), each containing its own header.
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 →