Meridian Lossless Packing: Difference between revisions

Audio file format

Meridian Lossless Packing, also known as Packed PCM (PPCM),^{[citation needed]} 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-quantization 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.