Image Processing Reference
There is room for both approaches, although at this stage in the game everyone is try-
ing to carve out market share at each other's expense. This will all evolve and unfold over
the next few years as the technologies are developed. For any of them to succeed, mutual
interoperability must ensure that they all succeed. It won't work if one company is domi-
Downloadable files are a potential delivery mechanism for low-bandwidth situations.
They might also be used to download content to a DVR device in something less than real
time. It may not matter how long it takes to transfer this material. It could be delivered
quickly, on a fast broadband or broadcast-transport mechanism, or slowly, via a modem
link. Table 27-2 enumerates some delivery times for the same broadcast-quality content
over several alternative links. It assumes H.264 video compression at 2 Mbps and trans-
ferring a clip of 5 minutes' duration.
It is clear from this table that DVR devices connected via dialup modems are not
going to have sufficient throughput and that a broadband connection at 500 Kbps or sig-
nificantly better is what is required.
The peer-to-peer model applies here. Some systems have a built-in limitation because the
delivery might be processed asynchronously due to the fact that upload speeds on ADSL
lines are lower than download speeds. This impedes the delivery of a stream but does not
matter for shared files unless the transfer is charged by the minute.
The trick-play capabilities tend to be implemented at an application level and are special
Recall our earlier discussion on GOP structures. To reconstruct every 8th frame in
order to play the video in a fast-forward mode will still require significant amounts of
work to decode the delta frames. Obviously, no processing power is required to display
Table 27-2 Delivery Times Versus Bit Rates
Estimated delivery time
Broadcast at 4.5 Mbps (normal MPEG-2 bit rates)
2 minutes, 15 seconds
Broadcast at 2 Mbps
Broadband 1 Mbps
Broadband 500 Kbps
Modem 56 Kbaud