Meridian Lossless Packing, also known as Packed PCM (PPCM), is a lossless compression technique for PCM audio data developed by Meridian Audio, Ltd. MLP is the standard lossless compression method for DVD-Audio content[1] (often advertised with the Advanced Resolution logo) and typically provides about 1.5:1 compression on most music material. All DVD-Audio players are equipped with MLP decoding,[2] while its use on the discs themselves is at their producers' discretion.
Dolby TrueHD, used in Archival Disc Blu-ray and HD DVD, employs the MLP codec, but compared with DVD-Audio, adds higher bit rates, 32 full-range channels, extensive metadata, and custom speaker placements (as specified by SMPTE).[3]
Standard DVD has a maximum transfer rate of 9.6 Mbit/s, around 70 percent of the bit rate needed to store 6 uncompressed audio channels of 24-bit/96 kHz. Should MLP not be able to compress the stream below the maximum transfer rate - or in case there is a need to reduce the size to fit overall disc capacity - it can exploit (lossy) pre-quantification zeroing out least significant bits when necessary.[4] [5] [6] The MLP stream can also contain "substreams", like surround and stereo downmix, which need not be of the same bit depth or sampling frequency - this further enables (lossy) pre-processing to save space. TrueHD streams cannot do this[7] (likely because Blu-Ray discs have higher storage capacity).
MLP is streamable: A decoder can pick up the stream and start decoding from that point on nearly instantly, where the encoder has inserted a "restart block" in the stream.[8] Typically, restart information is inserted approximately every 5 ms in the audio,[9] about the same as a typical 96 kHz FLAC stream.
| Media format | Status | Channels | Max. bit rate | |
|---|---|---|---|---|
| HD DVD | Mandatory | 2 to 8 | 18 Mbit/s | |
| Blu-ray | Optional | 2 to 8 | 18 Mbit/s | |
| DVD-Audio | Mandatory | 1 to 6 | 9.6 Mbit/s | |
| DVD-Video | Not available | |||