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DirecTV's 1st MPEG4 Satellite Launch Successful
tivoKlr writes "Looks like the 1st Spaceway satellite to provide "1500 channels of HD" has made it successfully into space. MPEG4 compression and local HD channels, something that the cable company can't offer in my area." Unfortunately the new satellite obsoletes the HD Tivo, and there's no word on when there will be a new one.
I believe the High Def Tivo uses MPEG2 for its data streams, won't be capable of decoding the MPEG4 streams.
Note that comm satellites are just 'bent pipes'. This keeps them simple and independent of changing technology. So, there likely isn't any MPEG4 technology on board the satellite. Rather, the technology will be in the ground station. Therefore, DirecTV could have used an existing satellite in orbit, or even shared space with someone else on a satellite...
Digital TV has 18 different formats (resolutions), 6 of which are considered "HD". A couple of them are equivalent to NTSC resolution; 640x480 pixels. So NTSC stuff would presumably be broadcast in the standard appropriate digital format, taking up less bandwidth than one of the HD formats.
Craig Steffen
http://www.craigsteffen.net
Yes, though not at the specific data rates used for broadcast. In general MPEG4 is vastly superior to MPEG2, however. Also, an MPEG2 stream would never be recompressed as MPEG4, the broadcaster would feed the uncompressed signal into the MPEG4 compressor. All in all this is a move to increase quality at the same bandwidth.
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The "killer technology" on the Spaceway birds are their ability to form tight "spot beams" using Ka band (~20 Ghz) downlink signals.
The spot beams are formed using a 1500 element phased array. The array can form as many as 780 downlink spot beams and 112 uplink spot beams across the US. Compare this with a typical Ku-band (~12 GHz) satellite which has a single beam over the entire US.
Spaceway uses digital regenerative switching of up to 10 Gbps, as opposed to the analog transponders of most geosynchronous communications satellites (despite the fact that most of those transponders are used with digital services these days).
Spaceway was originally supposed to provide satellite point-to-point and point-to-multipoint IP connectivity, but that was dropped in favor of providing massive localized HDTV capacity using spot beams.
Unfortunately, Ka band is more sensitive to rain fade outages than Ku band.
RawDigits: I would imagine an operation as large as DirecTV is probably not going to be re-encoding an MPEG2 signal, but using a more raw format for HD and compressing it from the 'master' copy just as they do when they convert to mpeg2 now ...
mecro: The FCC only gave broadcasters a small chunk of the spectrum to broadcast, which means the MPEG2 signal is compressed somewhere between 49-55:1.. That's insane, and MPEG 4 will hopefully lessen the compression ratio.
flimflam: Yes, though not at the specific data rates used for broadcast. In general MPEG4 is vastly superior to MPEG2, however. Also, an MPEG2 stream would never be recompressed as MPEG4, the broadcaster would feed the uncompressed signal into the MPEG4 compressor. All in all this is a move to increase quality at the same bandwidth.
For OTA signals, DirectTV and Dish currently have an antenna in the city that receives the analog OTA signal, which they compress for transmission. They only have a direct connection to the national signals they provide to people too far from local affiliates (I believe from NY and LA). It's unlikely they will obtain a more direct connection for digital OTA signals. So it's almost certain that the video will be doubly compressed--MPEG-2 by the channels, MPEG-4 by DirectTV.
Satellite channels (ESPN-HD, etc.) are currently pulled off of the high bitrate (MPEG-2) satellite feeds and compressed to low bitrate MPEG-2 by DirectTV and Dish. The encoder will likely be MPEG-4 for these types of sources.
jchapman16: Note that cable providers recompress the original MPEG2 streams themselves to reduce bandwidth used by HD channels.
I can't speak for every cable provider, but stream analysis done by those of us with FusionHDTV cards (capable of recording cable's QAM modulated HD streams) have shown that the video is not recompressed. It is re-wrapped, with much of the transport stream adjusted, but the data itself is not decompressed and re-compressed.
Xesdeeni
I've gotten to see a little bit of this, since my company (TandbergTV) is supplying the encoders. The bitrates on the mpeg-4 stream are going to vary from 4mbps to 20 mbps, which in mpeg-4 is pretty good looking. There's a load-balancing system that will adjust a channel's bitrate as it needs more (for say fast-panning scenes in sports). The encoders are installed now in two locations and running, but as with all projects this will take time.