Before content steering, multi-CDN routing happened at the URL level (different BASE-URI per CDN) or at DNS. Switching CDNs mid-session required restarting the player. Content steering changes this: the manifest references a steering manifest that lists available CDNs with priorities and weights, the player polls the steering manifest at intervals (typically 30–60 s), and updates which CDN it uses for subsequent segment fetches without restarting playback.
Apple's HLS Content Steering ships in iOS 17+ (2023) and is documented in the HLS Authoring Specification's content steering extension. DASH-IF added Content Steering to its 2023 IOP. Both formats use the same external steering manifest JSON spec (the DASH-IF content steering format), so a single steering server can serve both HLS and DASH players. Major players (hls.js since 1.4, Shaka since 4.6, dash.js since 4.7, AVPlayer natively) all support content steering as of 2025.
The operational use case is dynamic load shifting. When CDN A's edge in a region degrades, the steering server lowers A's priority for clients in that region, and players quickly migrate to CDN B without rebuffering. When CDN A recovers, the steering server raises it back. When a new event starts and CDN A's contracted capacity fills, traffic spills to CDN B. The steering server becomes the brain of multi-CDN delivery — typically built in-house using real-time CDN health data from observability tools.
