The bandwidth problem
A viewer's network speed changes constantly. A fixed quality stream either buffers on a slow link or wastes bandwidth on a fast one. Adaptive bitrate streaming solves this by offering the same video at several quality levels.
How it adapts
The source is encoded into multiple renditions, each at a different resolution and bitrate. The video is cut into short segments of a few seconds. The player measures throughput and buffer health, then picks the highest rendition it can sustain for the next segment.
The control loop
- Measure download speed of recent segments.
- Estimate what bitrate is safe.
- Switch up or down at the next segment boundary.
Why it fits a CDN
Each rendition's segments are plain cacheable files. The CDN serves them from the edge, so popular content scales out and switching between qualities is just requesting a different file. The player drives the decision, keeping the server stateless.
Key idea
Adaptive bitrate offers multiple cacheable renditions in short segments, letting the player switch quality per segment to match changing bandwidth.