Codecs

Table of Contents

DVD uses the MPEG-2 video codec (enCOder/DECoder) developed by the Moving Picture Experts Group to compress video data. This reduces storage and bit-rate requirements so that a standard-definition, full-length movie -- and then some -- can fit in 4.7GB and spool out to the display at less than 10 Mbps.

Newer, more advanced codecs reduce these requirements further by throwing away even more data and concealing the loss more cleverly. Examples of these new codecs include MPEG-4 Advanced Video Coding (AVC, aka H.264) and Windows Media Video 9 (WMV9), the latter recently adopted as a standard by the Society of Motion Picture and Television Engineers and renamed VC-1.

In general, the more compression, the lower the quality, but advances in codec algorithms mitigate this tendency. Today, MPEG-4 AVC and VC-1 can achieve the same picture quality as MPEG-2 using roughly half the bit rate, and that efficiency is likely to get better in the future.

In 2004, the DVD Forum approved three video codecs to be included as mandatory in all HD DVD playback devices: MPEG-2, MPEG-4 AVC, and VC-1. Most titles will probably use MPEG-4 AVC or VC-1 to squeeze as much as possible on to and out of a disc. Still, early titles will use high bit rates to maximize the picture quality; according to Mark Knox, a spokesman for the HD DVD Promotion Group, bit rates on early titles average around 20Mbps with peaks around 30Mbps. These rates will undoubtedly decrease over time as improvements are made in the codec algorithms.

On the audio side of things, HD DVD players must implement several audio codecs, but unlike DVD, which must have a Dolby Digital track as a minimum requirement, HD DVDs need not use any particular audio codec. The codecs that must be implemented in the player include Dolby Digital, Dolby Digital Plus, DTS in several flavors (including DTS-HD), MLP (Meridian Lossless Packing) for two-channel material (multichannel optional), and linear PCM for two-channel and multichannel content. Dolby TrueHD and DTS-HD Master Audio lossless decoding are optional but not required.

Squeeze Play

It's important to understand that, unlike DVD, HD DVD discs are not required to use any particular audio codec. Instead, the players are required to decode all of these formats (except Dolby TrueHD and DTS-HD Master Audio, which are optional), so content providers can use any of the authorized codecs they want.

  Maximum Resolution Bit Rate Maximum # of Channels
Dolby Digital 24-bit/48kHz 384-640kbps
(limited to 448kbps on DVD)		 5.1
Dolby Digital Plus 24-bit/48kHz 640kbps-3Mbps on HD DVD;
up to 6Mbps on Blu-ray		 7.1 (limited by disc formats)
Dolby TrueHD (opt.) 24-bit/192kHz
limited by disc formats)		 Up to 18Mbps peak on HD DVD;
up to 24Mbps peak on Blu-ray		 7.1 (limited by disc formats)
DTS 24-bit/48kHz (core),
24-bit/96kHz (extension)		 754kbps-1.5Mbps 5.1 (6.1 in DTS ES-Discrete format)
DTS-HD 24-bit/192kHz
(limited by disc formats)		 Up to 3Mbps on HD DVD;
up to 6Mbps on Blu-ray		 7.1 (limited by disc formats)
DTS-HD Master Audio (opt.) 24-bit/192kHz
(limited by disc formats)		 Up to 18Mbps peak on HD DVD;
up to 24Mbps peak on Blu-ray		 7.1 (limited by disc formats)
MLP 24-bit/96kHz
(limited by disc formats)		 Up to 18Mbps peak on HD DVD;
up to 24Mbps on Blu-ray		 2 required, 7.1 optional
Linear PCM 24-bit/192kHz 9.2Mbps 2
Linear PCM 24-bit/96kHz
(Blu-ray can deliver up to 24-bit/192kHz in audio-only version)		 18.5Mbps 8 (audio-only version)

Notes
The specifications that are "limited by disc formats" are not endemic to the associated codec, which can theoretically exceed these specs. The limitations are imposed by the HD DVD and Blu-ray formats. kpbs = kilobits per second

With MLP decoding, you might think that HD DVD players would be able to handle DVD-Audio discs, but alas, this is not so. Performing all the decoding listed above requires some serious DSP horsepower, which is why DVD-Audio is not supported. Highresolution, audio-only HD DVD titles are likely to start appearing as authoring facilities ramp up.

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