i
i
i
i
i
i
i
i
390 15. Using Multimedia in VR
In multimedia applications, timing is important, and all FilterGraphs are
designed so that they can be synchronized with a real-time clock. Whether
playing back video files or recording video from a USB webcam, all programs
need to keep up with this clock. If the hardwar e or application software
cannot deliver the samples through the graph fast enough then some samples
will have to be discar ded.
For example, a video recorder application is saving AVI movie
files from a DV camera with a compression filter in the chain.
For NTSC video, it must read, compress and write 30 samples
(frames) per second. But suppose the compression filter can only
compress 25 samples per second. The camera cannot be slowed
down, nor are