Mexican broadcaster Televisa is converting its primary program distribution from MPEG-2 compression to MPEG-4 AVC (advanced video coding) by installing an end-to-end system from Ericsson unit Tandberg Television to deliver its three networks to 258 affiliated stations across Mexico.
Televisa, the largest media company in the Spanish-speaking world, is the first major North American broadcaster to adopt MPEG-4, which is 50% more efficient than MPEG-2 in conserving bandwidth and which has been adopted by satellite operator DirecTV and various cable networks to launch new high-definition channels.
The MPEG-4 compression gear, which is scheduled to go live May 19 and which will replace existing Tandberg MPEG-2 encoders and decoders, will be combined with advanced DVB-S2 8PSK modulation equipment to maximize the efficiency of Televisa's satellite bandwidth.
According to William Aguirre, Televisa's chief of satellite broadcasting, the new transmission system will allow Televisa to deliver both HD and SD feeds in the same amount of satellite capacity—a 36 megahertz satellite transponder—that it was previously using to deliver just standard-definition feeds in MPEG-2.
The complete MPEG-4 transmission system selected by Televisa costs around $3 million and includes compression, modulation and conditional-access capabilities. It features Tandberg's EN8090 HD and EN8030 SD MPEG-4 AVC encoders, MX8400 IP multiplexers with Reflex statistical multiplexing, nCompass Control management system, Director distribution-control solution, SM6620 modulators with Prekor pre-correction technology for the broadcast headend, and RX1290 professional receivers for the affiliate sites. The stations will receive the MPEG-4 feeds, decode them to baseband, and then re-encode them in MPEG-2 using Tandberg ATSC encoders for local broadcast.
Televisa is currently testing the system from 1 a.m. to 5 a.m., and Aguirre says the picture quality holds up very well, despite the double compressions that distributing in MPEG-4 and broadcasting locally in MPEG-2 require. He attributes that to the advanced compression algorithms of the new MPEG-4 encoders.
“Of course, a double compression means a level of degradation in picture quality, but we're supporting a high level of quality for the end user,” Aguirre says. “With MPEG-4, you're improving the quality of the first compression.”
While Televisa is in the early stages of rolling out high-definition using the U.S. ATSC standard—the deadline for all Mexican stations to offer HDTV is 2021—it already offers seven hours of hi-def programming each day to affiliates in eight cities across Mexico. Until now, that has required leasing an additional transponder to support the HD feed, which was delivered at a bitrate of about 20 megabits per second (Mbps). Using MPEG-4, Televisa will be able to deliver better HD picture quality at 12 Mbps, Aguirre says. Combining that improvement with DVB S-2 8PSK modulation, which pushes through more bits for a given slice of transponder segment, will allow Televisa to use one transponder to transmit a multiplex of high-definition and standard-definition feeds.
While Televisa primarily offers HD content now on one network, Ch. 2, the MPEG-4 multiplex will eventually include three HD and three SD feeds, with the HD content sent at a bitrate of 7 to 12 Mbps and the SD feeds set at 6 to 8 Mbps.
“Basically in 27 megahertz you have both the HD and SD, and the remaining 9 megahertz we'll be using for special distribution initiatives, or some contribution stuff,” Aguirre says. “We're hoping to have the total [throughput] be 52-55 Mbps in 27 Mhz. SD, of course, is very important for us, as most of the country is working in SD now.”
In fact, only 32 Televisa stations will offer HD by 2009, representing less than 15% of the network's affiliate base. But Aguirre says that more and more stations will gradually roll out HD each year, particularly as Televisa expands its HD offerings past its primary Ch. 2 network to its other networks, Ch. 5 and Ch. 9.
How quickly other broadcasters will follow Televisa's lead remains to be seen. While MPEG-4 encoders generally cost 30% more than MPEG-2 gear, the savings in space segment that they realize have made them compelling to operations supporting multiple HD channels such as DirecTV, which selected Harmonic MPEG-4 encoders for its HD expansion, and HBO, which is using Motorola gear to convert its 26 networks to MPEG-4 for distribution to cable affiliates.
Broadcast networks are eyeing MPEG-4 for contribution feeds, such as satellite newsgathering applications, but because they don't distribute that many program feeds—primarily an East and West Coast feed—switching to MPEG-4 isn't as attractive.
“At this point, all these people are still in the MPEG-2 realm,” says Tom Lattie, director of broadcast and satellite for Harmonic. “A couple of networks have looked at the possibility of moving to AVC for primary distribution, but no one has yet.”
Fox isn't considering MPEG-4 for program distribution in the near term, says Richard Friedel, executive VP and general manager of Fox Networks engineering and operations. That's because to maintain a high picture quality for the end viewer, Fox actually uses Tandberg MPEG-2 encoders to compress its program feeds at “emission” rates suitable for local broadcast back at its Los Angeles network center. Affiliates use MPEG splicing technology to insert local branding and commercials, but don't recompress the video.
Matthew Goldman, VP of engineering for Tandberg, is still bullish about MPEG-4's near-term prospects in the broadcast market, and says Tandberg is in discussions with several major North American broadcasters besides Televisa about implementing MPEG-4 distribution.
The possibility of doing high-quality HD in the same space as an MPEG-2 standard-def feed is too compelling from an economic point of view to be ignored, Goldman says. He adds that new MPEG-4 receivers that can also support MPEG-2 and older modulation systems will make it easier for networks to handle the logistics of switching hundreds of affiliates to the new technology. So, says Goldman, “It's not about if they're going to do this, but when.”
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