An 18-month interoperability
testing program of HD satellite feeds by the World Broadcasting Unions-International
Satellite Operations Group, has found that that the industry has made great
strides in transmitting MPEG-4 HD video feeds via satellite using encoders and
decoders from different vendors.
The program, which involved 12 major equipment vendors and a
variety of HD formats, found that 83% of the tests produced an "unconditional
pass" for the transmission of high-definition content.
Slightly higher success rates of 86% to 87% were achieved
for 720p and 1080i feeds at either 10.3 Megabits per second or 20 Mbps with
MPEG-4 compression.
"Many customers are downlinking signals from multiple sources
and therefore multiple encoders," said Jack Vickers, product manager for receivers
and decoders at Sencore, one of the vendors with a product that performed well
in the tests. "MPEG-4 is almost a necessity, especially for HD over satellite
for bandwidth efficiency. So it is important for customers to be able to choose
a decoding MPEG-4 solution that fits well across the gamut."
This was the first MPEG-4 HD test the WBU-ISOG group had run,
so past comparisons of product interoperability were not possible.
"I would speculate, however, that we've come a very long way,"
Vickers said. "Overall, I was impressed with the test results, because most of
the vendors didn't have any real issues operating with one another."
The test was also important because it gives vendors an
opportunity to improve their product and make them better able to work with
other encoders and decoders, Vickers noted. Besides the overall results, he
said, Sencore was particularly pleased with low latency rates of its products
and their performance in the lip-synch tests.
"We were one of the top three in latency," Vickers said,
which is extremely important for live news and sports feeds.
Still, the test indicated some notable areas that vendors
will need to address in the future, particularly in formats that offer the highest-quality
HD feed.
The tests found that six of the 10 encoder vendors and three
of the nine decoder vendors did not support the higher-bit-rate 38 Mbps feeds
that offer the best HD quality.
There are presently just a handful of vendors that offer
H.264 solutions for 4:2:2 chroma sub-sampling, which offers a better-quality
image than the widely available 4:2:0 chroma sub-sampling encoders and decoders.
In the test, seven encoder vendors did not support 4:2:2 and
eight decoder vendors did not support 4:2:2. There was only one successful test
for 38 Mpbs at the 4:2:2 chroma.
Vickers noted that the group would like to hold additional
tests for the 4:2:2 products as they become available over the next year.
"The silicon that will lead to those solutions is just now
becoming cost effective," Vickers said. "It is something that is definitely on
our road map [and] I think next year you will see some large announcements
[from the major vendors] entering the market" with those features.
Vendors involved in the tests included ADTEC, ATEME, Cisco
Systems, Comtech TV, Evertz Microsystems, Fujitsu, Harmonic, International
Datacasting, NTT Electronics Corporation,
Sencore, Tandberg Television and Thomson
Grass Valley.
Full results for video, audio and lip synch tests
broken down by vendor can be found here.
