Image Processing Reference
In-Depth Information
44% increase in
catchment area
4 Mile Radius
3 Mile Radius
Figure 20-2
The effects of
π
R
2
on your
33% increase in radius
catchment.
20.8.7
Buffering
When the movie is played back on a PC or TV set-top box, the player expects that the data
will be made available in a timely manner. The output video runs on a timeline, and as
long as the data is provided (at least as fast as that timeline is being traversed) then the
playback experience will be smooth. Of course, the smoothness depends on the frame rate
that was selected when the video was compressed, but in any case it should be continu-
ous and consistent.
If you are streaming the video and cannot deliver the stream either continuously or
at a fast enough rate, then some kind of buffering becomes necessary. Modern client play-
ers are smart enough to negotiate with the streaming server to select a content stream that
is deliverable within the available physical bit rate. This bit rate is measured across the
connection during the session, and the content can be negotiated up or down as the avail-
able bit rate changes.
The calculation may involve some computation based on the length of the video and
should also take into account the buffering space available and the delivery speed. This
yields a buffering time that loads perhaps 30 seconds of video before the playback com-
mences. Figure 20-3 shows a partly loaded buffer where the playback has already
commenced. The buffer must be filled with new material until the end of the transmission
without the playback process catching up.
Once playback begins, the content continues to be delivered from the streaming
server while the player uses the buffered bit stream from the other end. Ideally, the play-
back will just about catch up with the download at the end of the video.
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