Content starts

The Content starts metric counts sessions in which main content actually began playing. Unlike Media starts, it excludes sessions that ended during pre-roll ads, buffering, or stalls. This makes it the right denominator for completion and engagement rates.

How this metric is calculated

The media backend sets mediaReporting.sessionDetails.isPlayed = true the first time a media.play event for main content is received. The metric is triggered on that play event but reported on the close call. To compute the pre-roll drop rate, use (Media starts − Content starts) / Media starts.