Data transfer
The rate of data transfer from the disc to the playback processing unit determines the quality of application on offer such as SD or HD video resolution, audio mode, level of interactivity and games. Two transfer rates are specified: data transfer rate and video/audio transfer rate in maximum Mbps. For the traditional DVD format, the data rate is 11.08 Mbps and that for video/audio is 10.08 Mbps with a maximum video bit rate of 9.8 Mbps. The average video bit rate is in the region of 5 Mbps which is adequate for standard definition video (720 X 576i or 720 X 480i). The figures for HD DVD are 36.55 Mbps for both data and video/audio with maximum video bit rates of 28.0 Mbps. In the case of the Blu-ray format, the maximum data transfer rate is 36.0 Mbps and that for the video/audio at 1.5X speed mode is a staggering 54.0 Mbps. This gives a maximum video bit rate of 40.0 Mbps. Both HD DVD and BD formats are thus suitable for high-definition resolu- tion namely 1920 X 740p, 1920 X 1080p and 1920 X 1080p. High-definition video is not necessarily confined to blue-laser-based discs. Using MPEG-4 AVC/AAC encoding, a X3 DVD-ROM has the capacity (8.4 GB) to store 120 min of HD video at a transfer rate of 3 X 10.08 = 30.24 Mbps, the same transfer rate as a single-speed HD DVD disc.
Table 20.5 compares the main properties of the three DVD formats: DVD, HD DVD and BD.
The symmetry between DVD and HD DVD formats enables the two formats to be combined on a single disc configuration designated as ‘Combination’ and ‘Twin Format’. The purpose of these configurations so that consumers with a standard DVD player can buy the backward com- patible discs and use them in full and when they are ready for an HD DVD player, they will could play the same discs, but this time making full advantage of the higher density data. Combinational discs are double sided, with HD DVD on one side and DVD on the other. Twin format con- figuration are DL SS discs with HD DVD on one layer and DVD on the other layer.