Codecs
Codecs are compression schemes that store audio and video more efficiently, either giving longer play time or higher quality per megabyte. There are both lossy and lossless compression techniques.The BD-ROM specification mandates certain codec compatibilities for both hardware decoders (players) and the movie-software (content). For video, all players are required to support MPEG-2, H.264/AVC, and SMPTE VC-1. MPEG-2 is the codec used on regular DVDs, which allows backwards compatibility. H.264/AVC was developed by MPEG and VCEG as a modern successor of MPEG-2. VC-1 is another MPEG-4 derivative codec mostly developed by Microsoft. BD-ROM titles with video must store video using one of the three mandatory codecs. Multiple codecs on a single title are allowed.The choice of codecs affects the producer’s licensing/royalty costs, as well as the title’s maximum runtime, due to differences in compression efficiency. Discs encoded in MPEG-2 video typically limit content producers to around two hours of high-definition content on a single-layer (25 GB) BD-ROM. The more advanced video codecs (VC-1 and H.264) typically achieve a video runtime twice that of MPEG-2, with comparable quality.For audio, BD-ROM players are required to support Dolby Digital AC-3, DTS, and linear PCM. Players may optionally support Dolby Digital Plus, and lossless formats Dolby TrueHD and DTS HD. BD-ROM titles must use one of the mandatory schemes for the primary soundtrack. A secondary audiotrack, if present, may use any of the mandatory or optional codecs.For users recording digital television programming, the recordable Blu-ray Disc standard’s datarate of 54 Mbit/s is more than adequate to record high-definition broadcasts from any source (IPTV, cable/satellite, or terrestrial). For Blu-ray Disc movies the maximum transfer rate is 48 Mbit/s (1.5x) (both audio and video payloads together), of which a maximum of 40 Mbit/s can be dedicated to video data. This compares favorably to the maximum of 30.24 Mbit/s in HD DVD movies for audio and video data.