--- title: transitionID framework: coremedia role: symbol role_heading: Type Property path: coremedia/cmsamplebufferattachmentkeydefinitions/transitionid --- # transitionID Marks a transition from one source of buffers to another. ## Declaration ```swift static let transitionID: CVAttachmentKeyDefinition ``` ## Discussion Discussion During gapless playback of a list of songs, this attachment marks the first buffer from the next song. If this attachment is on a buffer containing no samples, the first following buffer that contains samples is the buffer that contains the first samples from the next song. This transition identifier should be unique within a playlist, so each transition in a playlist is uniquely identifiable. A counter that increments with each transition is a simple example.