---
title: "Choose which video renditions to precompute"
description: "Balance adaptive bitrate quality, transcoding cost, origin load, and CDN hit rate when deciding which variants to materialize."
canonical_url: "https://fanout.sh/system/archive/adaptive-bitrate-and-cdn-decider"
md_url: "https://fanout.sh/system/archive/adaptive-bitrate-and-cdn-decider.md"
access: "public"
---

# Choose which video renditions to precompute

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

## Public overview

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.

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