Combining video streams in composite video stream with metadata

A combiner system may be provided for combining, in a compressed domain, video streams of different media sources in a composite video stream by including a respective video stream as independently decodable spatial segment(s) in the composite video stream. The combiner system may generate composition metadata describing a composition of the spatial segments in the composite video stream and identification metadata comprising identifiers of the respective video streams. A receiver system may obtain decoded video data of a respective video stream based on the composition metadata and a decoding of the composite video stream, and based on the identification metadata, identify a process for handling the decoded video data. Thereby, the composition of spatial segments may dynamically change, while still allowing the receiver device to correctly handle the spatial segments.