HD DVD and Blu-ray Disc
The maximum number of discrete coded channels is the same for both formats: 7.1. However, HD DVD and Blu-ray Disc impose different technical constraints on the supported audio-codecs. Hence, the usage of DD+ differs substantially between HD DVD and Blu-ray Disc.
| Codec | HD DVD | Blu-ray Disc | ||||
|---|---|---|---|---|---|---|
| Decoding | Channels | Bitrate | Decoding | Channels | Bitrate | |
| AC-3 | mandatory | 1 to 5.1 | 504 kbit/s | mandatory | 1 to 5.1 | 640 kbit/s |
| E-AC-3 | mandatory | 1 to 7.1 | 3.0 Mbit/s | optional, available for rear channels only | 6.1 to 7.1 | 1.7 Mbit/s |
| TrueHD | mandatory optional |
1 or 2 3 to 8 |
18.0 Mbit/s 18.0 Mbit/s |
optional | 1 to 8 | 18.0 Mbit/s |
On HD DVD, DD+ is designated a mandatory audio codec. An HD DVD movie may use DD+ as the primary (or only) audio track. An HD DVD player is required to support DD+ audio by decoding and outputting it to the player's output jacks. As stored on disc, the DD+ bitstream can carry for any number of audio channels up to the maximum allowed, at any bitrate up to 3.0 Mbit/s.
On Blu-ray Disc, DD+ is an optional codec, and is deployed as an extension to a "core" AC-3 5.1 audiotrack. The AC-3 core is encoded at 640 kbit/s, carries 5 primary channels (and 1 LFE), and is independently playable as a movie audio track by any Blu-ray Disc player. The DD+ extension bitstream is used on players that support it by replacing the rear channels in the 5.1 setup with higher fidelity versions, along with providing a possible channel extension to 6.1 or 7.1. The complete audio track is allowed a combined bitrate of 1.7 Mbit/s: 640 kbit/s for the AC-3 5.1 core, and 1 Mbit/s for the DD+ extension. During playback, both the core and extension bitstreams contribute to the final audio-output, according to rules embedded in the bitstream metadata.
Read more about this topic: Dolby Digital Plus
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