Image Processing Reference
be trivial on their own but significant when you cascade them together. For some program
material, that may involve lossless compression from a remote OB (outside broadcast) or
secondary studio delivering a feed to a transmission hub that aggregates several sources.
This presents some interesting issues with synchronization when locking the video
to real-world time. The typical delay between analog terrestrial and digital terrestrial in
the United Kingdom (where the comparison can be made very easily) is approximately
half a second. For most program material this is not going to matter.
Latency in Videoconferencing Systems
Videoconferencing is deploying more video encoders as users get interested in the idea of
seeing one another while they chat. The Apple iChat AV videoconferencing system is built
around the H.264 codec. For this application the codec is configured to send the output of the
video camera with zero latency. Zero latency is accomplished by eliminating the B-frames
and sending a sequence that only contains I-frames and P-frames. Eliminating B-frames also
reduces the size of the GOPs so they are effectively just one or two frames long.
Hardware Versus Software
In terms of sheer performance, hardware solutions are always going to deliver better qual-
ity than software, the major limitation being that they are hard to upgrade. This is being
addressed by using specialized DSP chips that are reloaded with new codec algorithms.
An upgrade can be delivered and rolled out very easily without needing to open the box.
Another solution is hardware-assisted software. This will become more popular as graph-
ics cards are deployed with embedded encoding and decoding support for video.
Companies such as Texas Instruments, Ateme, Harmonic, and Equator are working on
products based on this technique.
The graphics cards made by NVidia are already being manufactured with onboard
video compression processing. It remains to be seen how software developers exploit this
New versions of the chipset used in graphics cards made by NVidia now have video
encode/decode for a variety of formats built in. This may lead to innovative solutions for
Texas Instruments: http://www.ti.com/
Texas Instruments Semiconductors: http://support.ti.com/
Equator Technologies: http://www.equator.com/