A signaling method and device for use in stream switching in which GDR random access points are used. In order to indicate the GDR switching points in the bitstreams, a Sync Sample Information Box, which is contained in a Sync Sample Box, is used to provide information of such GDR switching points. The information also includes which slice group is the isolated region and which slice group is the leftover region, if slice groups are applied in encoding. The signaling method can be used in video data transmission using Real-time Transport Protocol (RTP), and a Session Description Protocol (SDP) can be used to convey information indicative of the characteristics of the bitstreams.