An example ladder
These are illustrative figures for H.264 at up to 30 frames per second. The right numbers depend on codec, frame rate and the content itself.
- 2160p (4K) at about 16 Mbps
- 1440p at about 9 Mbps
- 1080p at about 5 Mbps
- 720p at about 3 Mbps
- 540p at about 1.8 Mbps
- 360p at about 0.8 Mbps
- 240p at about 0.4 Mbps
Designing a ladder
- Top rung: the best quality your audience's screens and connections can use
- Bottom rung: low enough to keep playing on a poor mobile connection
- Spacing: each rung roughly 1.5 to 2 times the bitrate of the one below, so switches are neither jarring nor pointless
- Count: four to seven rungs for most services
- Alignment: identical keyframe positions on every rung, so switching is seamless
Fixed, per-title and per-scene ladders
A fixed ladder applies the same rungs to every title. It is simple and wasteful: animation gets far more bitrate than it needs and fast sport gets too little.
Per-title encoding analyzes each video and builds a ladder to suit it, which commonly cuts delivery volume substantially for easy content at no loss of quality. Per-scene or content-aware encoding goes further and varies the settings within a title.
Why the ladder matters commercially
The ladder sets both the quality viewers see and the size of your delivery bill, since the bill follows the average bitrate delivered. It also sets storage and encoding cost: every extra rung is another copy of every title.
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