Ladder Design and Rung Selection

A delivery ladder is a set of resolution and quality steps offered to a player so it can pick one that fits the current network. Designing that set is a question of measurement: each rung must earn its place, and no two rungs should sit so close that a player switches between them for no visible gain.

Start from the audience

List the devices and the network classes the audience actually uses. A rung exists only if some real class needs it. A ladder tuned on a fast office network can waste five rungs on a mobile audience that lives in two. The first measurement, then, is not of a codec but of the audience spread.

Space the rungs

Two neighbours should differ enough that a switch is visible in size or in quality, but not so much that a viewer feels a jump. In practice a resolution step of one tier, or a quality step of two to three points on the rate factor, keeps the set tidy. Compute the join points from the distortion curves rather than from habit.

Per-title versus one ladder

A fixed ladder is cheap to operate and easy to cache. A per-title ladder measures each asset and stores its own rungs, which saves bits on easy content but multiplies the storage and the quality-control work. The desk recommends a fixed ladder with a small number of content classes, and a per-title pass only where a title is watched enough to pay for the extra work.

Keep a floor and a ceiling

Every ladder needs a low floor for a weak link and a high ceiling for a large screen. The floor should stay in the widest-supported codec so nobody is stranded. The ceiling can use the newest codec, because only the strongest devices reach it. Anchors for both ends are on the 1080p and 4K sheets.