Dolby TrueHD - Dolby TrueHD is a "lossless" compression codec. Although it is compressed to take up less disc space than a PCM track, once decoded it is bit-for-bit identical to the studio master (at either 16-bit or 24-bit resolution, at the discretion of the studio). It may help to think of it like a ZIP file that holds a PCM track. Once you unZIP the file, you get a 100% identical copy of the original PCM, without compromising any sound quality. TrueHD is an optional format on Blu-ray. TrueHD is not built in a core+extension configuration, Blu-ray discs that contain a TrueHD track are also required to contain a standard Dolby Digital AC-3 track for compatibility with players that don't support TrueHD.