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What do Networks use to grab OTA satellite feeds?  

post #1 of 9
Thread Starter 
So lets say CSI on CBS is recorded by the local station in HD format.

What kind of equipment do they use to record it and then later re-transmit it at the appropriately scheduled broadcast time?
post #2 of 9
Quote:
Originally posted by patriot76
So lets say CSI on CBS is recorded by the local station in HD format.

What kind of equipment do they use to record it and then later re-transmit it at the appropriately scheduled broadcast time?
CBS for example transmits MPEG2 at 45mbs over satellite or standard DS3 phone lines. The station has equipment to convert this back into standard SMPTE292 HD digital video. That is a serial signal at 1.5gbs (gigabits per second). Broadcast VTR's and Disk recorders (servers) can accept this signal and record it, with the exception of a few units in a re-compressed DCT form. Recording HDTV at uncompressed rates is very expensive. Either a LOT of disk space or use of a D6 VTR with raw tape at $400 per hour.

They then simply play it back through thier ATSC encoder. It is also possible to record the native 45mbs stream on a server and play that back through a re-encoder to ATSC though no hardware exists that I am aware of.

Can you buy this equipment and record HDTV off a DBS receiver's analog HDTV out. Yes you can, it's a free market.

HDTV VTR starting at $50,000
conversion device analog HDTV to SMPTE292 - $5000 to 10,000
conversion device SMPTE to analog HDTV for playback $2500

Audio? (assumes an HDTV vtr with 8 channels)
AC3 decoder

TAPE? starting at about $70 per hour.

So go for it. This is why image constraint is veiwed as such a joke by those in the broadcast business. But the price of this stuff will decrease over the next few years. But by that time consumer analog HDTV can be phased out as well.
post #3 of 9
That's really the hard way to do it, and has a bunch of problems. There's no reason to go anywhere near analog.

I don't know anything about DS3 distribution to affiliates (why would anyone spend that kind of money?) but I used to work for a company that made some of the equipment you'd use to do it "the easy way."

Satellite MPEG2 distribution is a 27Mbps MPTS transport. One of programs in the CBS feed is the HD signal. It's never more than 19.4Mbps, of course, but it's usually more like 10-12Mbps. To receive this, you'd use an MPEG2 IRD with a DVB-ASI or DHEI out. DVB-ASI is a serial digital signal on coax that maxes out at 216Mbps, but is rarely seen at more than 54Mbps. (The maximum for 256QAM in an 8MHz (European) broadcast/cable channel) DHEI is the GI/Motorola proprietary equivalent, limited to 45Mbps, on glorified VGA cables, limited to 12', etc, etc. Never seen outside cable head-ends, thankfully.

Most professional IRDs will happily output the HD MPEG2 stream, though their onboard decoders probably won't output the analog HD signal. (Many won't even decode 4:2:2, but will still give you the bitstream, decrypted if necessary/authorized)

So now you have the compressed video. Pipe this directly into a server. SeaChange and nCube will sell these to you, or you could write your own and use ViewGraphics (now OptiBase) MediaPump cards. (PCI card with DVB-ASI I/O)

You'll probably still pay $50k for the server, but the recievers are cheap ($2500) and the modulator you already have if you're in the DTV business. You might even have the server, if you had any intention of selling local ads on your DTV broadcasts.

And (and this is important) you only need the server if you're going to time shift. Most network affiliates don't even try to timeshift SD. (Hence the "9pm (8pm Central)" Nonsense.)

Time to play the show for broadcast? Play out of your server into your 8VSB modulator. ASI in, IF out. Feed your transmitter and you're done.

This, by the way, preserves exactly (bit-for-bit) the image quality of the original network downlink. If you decode and re-encode at any point, your outbound signal quality is degraded, because you're decompressing and recomressing the image. (For an example, take a nice JPEG image, convert it to .BMP and back to JPEG. Repeat. Pretty soon the image starts to look like crap.) Going to analog is even worse, for reasons I don't need to rehash for this audience.

Local cable companies can do the same thing, btw, but they're likely to pick up the affiliate off-air with an 8VSB receiver with an ASI output.
post #4 of 9
Quote:
Originally posted by n6mod


One of programs in the CBS feed is the HD signal. It's never more than 19.4Mbps, of course, but it's usually more like 10-12Mbps.
HDTV is at 1.5gbs in the studio enviornment. CBS does not want to go down to 19.4mbs to affiliates because it must be decompressed and cut in with local programming. That can only be done with the network signal in baseband form. You can't splice MPEG streams together with single frame accuracy and television is a frame accurate business. The local station bugs aslo need to be keyed in, like it or not. This too requires a baseband signal. The higher the initial bit rate, the less compression contantination artifacts. DS3 is used because it is a standard telephone company service.

DVB ASI runs at 270mbs, the same bit rate as SDTV digital video, SMPTE259. This is so that standard SDI routing and distribution can distribute ASI as long as no signal inversion takes place as ASI is NRZ coded.
post #5 of 9
Obviously you have more specific information about how CBS does things, but I'm very surprised about a few things.

CBS has a reputation for being extremely quality conscious. As such, I'm quite surprised that they will allow decode-recode cycles.

Now, are you saying that CBS does their distribution to affiliates at >19.4Mbps? They surely don't distribute uncompressed HD, do they?

As to the why DS3 comment, I'm surprised that they bother with landlines for distribution. I don't see how that can be cost effective when the infrastructure is in place for satellite distribution.

You do have to wait for an I-frame to splice MPEG2, but that's rarely more than 15 frames. With a little attention to the initial encoding, you can ensure that there are I-frames at your splice points anyway. Take a look at DVS253 and DVS380 for details on doing digital-into-digital ad insertion.

Bug insertion is a stickier problem without going to baseband, and I'd moved on from Terayon before they got that working. BigBand claims to have done it, but I never saw it running.

I've always seen ASI spec'd at 216, but that might be a difference between payload and line rate. As to using SDI dist. amps... I tried to avoid that, since the times I tried it, half the outputs were inverting, and therefore didn't work for ASI.
post #6 of 9
Quote:
Originally posted by n6mod
Obviously you have more specific information about how CBS does things, but I'm very surprised about a few things.

CBS has a reputation for being extremely quality conscious. As such, I'm quite surprised that they will allow decode-recode cycles.

Now, are you saying that CBS does their distribution to affiliates at >19.4Mbps? They surely don't distribute uncompressed HD, do they?

As to the why DS3 comment, I'm surprised that they bother with landlines for distribution. I don't see how that can be cost effective when the infrastructure is in place for satellite distribution.

You do have to wait for an I-frame to splice MPEG2, but that's rarely more than 15 frames. With a little attention to the initial encoding, you can ensure that there are I-frames at your splice points anyway. Take a look at DVS253 and DVS380 for details on doing digital-into-digital ad insertion.

Bug insertion is a stickier problem without going to baseband, and I'd moved on from Terayon before they got that working. BigBand claims to have done it, but I never saw it running.

I've always seen ASI spec'd at 216, but that might be a difference between payload and line rate. As to using SDI dist. amps... I tried to avoid that, since the times I tried it, half the outputs were inverting, and therefore didn't work for ASI.

To summarize your questions:

No network can afford to transmit baseband HDTV across any path so some compression is required. 45mbs is better than 19.4 and fits nicely into standard DS3 lines. Not all affiliates are served by satallite. PBS does use 19.4. This is to keep equipment costs low to affiliate stations, a sensitive issue in PBS.

Many coimapnies both in the broadcast industry and in other industries have/are working on MPEG splicing and some day it will be practical. But today it's a problem in broadcast operations. 15 frames is a lot of time to be uncertian.

You are correct ASI payload is 216mbs. The overhead is padding to keep it compatable with SDI equipment. In telco systems they may use another transport package and keep it a 216mbs.

A lot of skilled telecommunications engineers here like yourself are often mystified as to the way things are done in broadcast engineering. There are many reasons one of which is we are a small industry compared to the telecommunicatios industry as a whole. A lot of our hardware never exceeds 5000 units built. HDTV / DTV is new and not yet fully accepted by the public. The old SDTV NTSC infrastructure must still be supported and in finnancial terms is the most improtant today. There are presently many problems running dual feeds and cutting in commercials and SDTV material. As DTV in general becomes more widespread and technology advances, many of these now expensive workarounds will be improved.
post #7 of 9
Glimmie,

Thanks for your patient replies, though I think you misunderstand my background. I'm a networking guy who's just spent five years in cable, both on the cable modem and MPEG2 sides of the house. (As an aside, Terayon recently acquired Digitrans, who made the 4:2:2 recievers in use at a large number of CBS affiliates. They were the satin black receivers with GI badges on them...DSR-4810, I think?)

In any case, you might want to take a look at the white paper linked from here. This applies equally to HD, though the CherryPicker can't recode HD yet.

And we're now drifting way off topic, but this is a fasicnating conversation.... < n6mod at milewski dot org > if you'd like to continue it.

-Z
post #8 of 9
Glimmie,
Your not quite correct here, PBS is feeding 19.39 Mbs direct from satellite and you can capture it on a server for later playback intact. A company called Agilevision has a unit that can MPEG bit splice without having to de-compress and re-compress but its costly ($250K). Here we are only carrying the HD feed on WKPC at this time and we cut to the satellite feed direct and switch back to our normal programming when its over. cost was under $20K including sat receiver, switcher, and we interfaced it to the transmitter remote control system.

So yes it can be done your way but this is a whole lot cheaper and doesn't require an HD infrastructure just a simple system and server.

William
post #9 of 9
Quote:
Originally posted by Glimmie


HDTV VTR starting at $50,000
conversion device analog HDTV to SMPTE292 - $5000 to 10,000
conversion device SMPTE to analog HDTV for playback $2500
.
Actually, I just attended the Government Video Expo here in DC. I spoke to the Sony and Panasonic reps. The HDTV VTRs have come down a little bit. They had one "field" model that was around $25,000 rather than $50,000.

Here's a good web site that includes a FAQ about Sony's HDCAM VTRs:

Sony HDCAM VTR FAQ

Brett
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