DVD Demystified

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Figure 6.33
Examples of camera
angles
TABLE 6.34
Data-Rate
Limitations for
Camera Angles
Chapter 6
changed with commands on the disc. The alternate chunks of video must all
be the same length. The viewer cannot switch to a different camera angle
and have the action be out of sync (unless the video itself was not produced
in sync). Each angle is technically required to have identical audio tracks,
but it is possible to get around this requirement and assign a different
audio track to each angle.
Video objects, one for each angle, are interleaved into an interleaved
block (ILVB). ILVBs are required for camera angles and optionally can be
used for parental branching and seamless branching (see Figure 6.33).
A major advantage of camera angles is that they are supported directly
by the buffer management feature of DVD, which automatically leapfrogs
through the interleaved video objects, reading only the ones assigned to the
selected angle. This means that adding an angle does not reduce the data
rate limit, although it does reduce playing time. For example, a single-angle
program that runs for 5 minutes at 7 Mbps would be about 262 megabytes
long. If it were changed to a two-angle program, each angle could still run
at 7 Mbps, but the program would take up 524 megabytes. Limitations are
imposed on the maximum data rate depending on the number of angles (see
Table 6.34). The data-rate limit applies to the angle block and for 2.5 seconds
preceding the angle block.
Angles Maximum Data Rate for Each Angle
2 to 5 7.8 Mbps
6 to 8 7.3 Mbps
9 6.8 Mbps