A DVD-Video disc can have up to 8 audio tracks, with each track being PCM, MPEG-2, or Dolby Digital.
PCM is uncompressed digital audio - the same format used on CDs. Having from one to eight channels, it can be sampled at 48 or 96 kHz with 16, 20, or 24 bits per sample. Audio CD is limited to 44.1 kHz at 16 bits, with a maximum bitrate of 6.144 Mbps. DVD players support all the variations of PCM, but some of them may subsample 96 kHz down to 48 kHz, and some may not use all 20 or 24 bits.
MPEG audio is multi-channel digital audio, using compression with sample rate of 48 kHz at 16 bits. Both MPEG-1 and MPEG-2 formats are supported. The variable bitrate is 32 kbps to 912 kbps, with 384 being the normal average rate. MPEG-1 is limited to 384 kbps. MPEG-2 surround channels are in an extension stream matrixed onto the MPEG-1 stereo channels, which makes MPEG-2 audio compatible with MPEG-1.
* Dolby Digital is multi-channel digital audio, with a sample rate of 48 kHz at up to 24 bits. The bitrate is 64 kbps to 448 kbps, with 384 being the normal rate for 5.1 channels and 192 being the normal rate for stereo, although most Dolby Decoders support a slightly higher bitrate.
NTSC-formatted discs must use PCM or Dolby Digital on at least one track. PAL-formatted must use PCM or MPEG audio or Dolby Digital on at least one track. Additional tracks may be in any format.
For stereo output, all players have a built-in 2-channel Dolby Digital decoder. This decoder mixes 5.1 channels down to Dolby Surround stereo. PAL players also have an MPEG or MPEG-2 decoder. Both Dolby Digital and MPEG-2 support 2-channel Dolby Surround. A DVD labeled Dolby Digital may only use the L/R channels for surround or "plain" stereo.
* Confidential Unpublished Works. Copyright 1992-1997 Dolby Laboratories, Inc. All Rights Reserved.