Choose which video renditions to precompute

Balance adaptive bitrate quality, transcoding cost, origin load, and CDN hit rate when deciding which variants to materialize.

Adaptive Bitrate And CDN Decider

Adaptive bitrate streaming lets the player switch between video variants based on network, device, and buffer conditions. A CDN decider decides which variants are worth precomputing and caching.

The player downloads a manifest that lists variants:

As conditions change, the player switches.

HLS is one common packaging format: playlists reference ordered media segments, and master playlists reference variant playlists.

Eager vs Lazy Transcoding

generate all variants at upload time, good playback readiness, expensive for long-tail videos nobody watches.

generate baseline variant first, generate higher variants on first demand or popularity threshold, cheaper for long-tail content, first request may pay delay.

channel popularity, current view velocity, geography of viewers, content type, recent shares, trending service signal, expected event/live spike.

transcode more variants, push/warm CDN, keep at origin, evict from CDN, use cheaper storage tier.

Signal Likely Decision --- --- new upload, no viewers baseline variant only; no prewarm high subscriber channel generate common variants eagerly sudden view velocity prewarm top regions and protect origin regional spike push only to affected CDN geography old long-tail video keep manifest; move segments to colder storage repeated variant.missing events generate that rendition and update manifest

The decider should be conservative with expensive actions. A false positive wastes transcoding and CDN storage; a false negative creates a slower first playback.

The manifest is part of the product contract. The player must know how to react when:

only the baseline rendition exists, a higher rendition appears during playback, a segment returns 404 from CDN but exists at origin, a CDN region is unhealthy, the viewer is on a metered or low-power device.

Prefer fallback behavior over hard failure. For example, retry a missing 1080p segment at 720p before surfacing an error.

Track CDN hit ratio by variant, origin shield traffic, manifest error rate, startup delay, rebuffering time, bitrate switches, and first-play delay for lazy variants. These metrics connect economic decisions to playback quality.