Block Duration

The block duration — the duration of ad block in the playlist settings — sets the length of the block, the rhythm unit the whole playlist is built around. Typical values are 60 or 120 seconds.

What it affects

Aspect	Effect of block duration
Frequency semantics	"Plays per block" and starting blocks are counted in blocks of this length.
Distribution quality	The engine balances spacing within and across blocks of this length; a well-chosen block duration is the foundation of even distribution.
Loop length	The loop is a whole number of blocks; the block duration and the campaign periods together determine how many — see Playlist Structure.

Aspect

Effect of block duration

Frequency semantics

"Plays per block" and starting blocks are counted in blocks of this length.

Distribution quality

The engine balances spacing within and across blocks of this length; a well-chosen block duration is the foundation of even distribution.

Loop length

The loop is a whole number of blocks; the block duration and the campaign periods together determine how many — see Playlist Structure.

Choose it deliberately

Pick a block duration that matches your sales model — if you sell "one spot per minute", the natural block is 60 seconds. Then keep campaign periods harmonious with it, per the guidance in Choosing periods.

The block duration can be left unset, but should not be. It gives the engine the rhythm to optimize against and makes fine-grained placement quality possible. Always set a block duration in production.

Blocks under pressure

Two situations make actual blocks deviate from the nominal duration — both are expected, bounded, and reported:

Mixed-length ads. A campaign rotating ads of different lengths makes individual blocks run slightly over or under nominal; the drift is bounded by the length difference and balances out across the loop. See Groups with different footprints.
Overbooking. When demand exceeds capacity, the effective block stretches (policies that keep everyone) or shrinks (policies that drop the excess) — see Overbooking behavior. The engine keeps the block and all periods in step with each other, so the playlist stays rhythmically consistent.