RFC: idea/parts for digitizing raw analog HD to disk - AVS Forum
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post #1 of 16 Old 01-03-2002, 09:40 AM - Thread Starter
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960x540p 4:2:2 HDTV recorder:

A (1) Analog Devices AD9888 triple 8 bit ADC

Takes 3 (Y,Pb,Pr) analog 74.25 MHz inputs and outputs 6x8 bit digital lines, each with 37.125 MHz clock

Call them Y1,Y2,Pb1,Pb2,Pr1,Pr2

B (3) Maxim 3690 8:1 serializers on Y1,Pb1,Pr1 (297 MHz)

going from 1920 horizontal to 960.

C (3) Maxim 3885 1:16 deserializers on Y1,Pb1,Pr1 (18.5625 MHz)

call them Y0-15, Pb0-15, Pr0-15

D (1) National Instruments PCI-DIO-32HS (32 bits up to 19.9 MHz, costs $1k) connects to Y0-15, Pb0-7 and Pr0-7

960 x 540p 4:2:2 (Pb, Pr at 480x540p)

E (5) RAID array of disks for recording the 18.5625x32 = 594 Mb/s (74.25 MB/s) to disk.

OR alternatively replace B,C,D with

B (3) Rockwell 8:64 (192 bits at 4.640625 MHz, use 64 + 32 +32 or 128 bits for 4:2:2)
C (x) cheap PCI digital input card(s) that can DMA 128 bits at above clock rate

Comments?

-Benson
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post #2 of 16 Old 01-03-2002, 10:00 AM
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At 594 Mbits/second, a 2 hour movie would occupy 535 Gigs.

Today, that's an expensive way to store Hidef.
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post #3 of 16 Old 01-03-2002, 10:04 AM
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You will need clock generation circuitry for the ADC clocks. This must be locked to the incomming video.

What is the Maxim 3690? To get 1920x1080i down to 960x540p will require substantial memory to store at least one field of the 1920x1080i. If proper interlace removal is to be done with film material up to 5 fields must be stored and analyzed.

A lot of glue logic will be needed to interface these chips together. Those parts aren't cheap at the speeds you will require not to mention the compiler tools.

The storage requirements will kill you at these bit rates.

As any HDTV you receive is at 19.4mbs max, why go to the trouble to record it at these rates? If you want a project, build an ATSC MPEG2 encoder. Now you can take analog out of any STB and record it on standard DVHS machines or a HiPix equipped computer.

But this still won't get you around image constarint when it is applied. And at that point, just buy the DVD because that's the best it's going to look.

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post #4 of 16 Old 01-03-2002, 10:10 AM - Thread Starter
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cymro,

Agreed. However, you've got to trade off simplicity of design vs. storage requirements. Either you pay for lots of storage or for a more complicated design involving compressing parallel streams and all the problems that entails. Unless a product like this goes high-volume, but it couldn't.

-Benson
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post #5 of 16 Old 01-03-2002, 10:54 AM - Thread Starter
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Glimmie,

Good points all.

The AD9888 will lock to the incoming video-- see <http://products.analog.com/products/...product=AD9888>

The Maxim 3690 is at <http://dbserv.maxim-ic.com/quick_view2.cfm?qv_pk=1904>

Really what I would like is an 8:16, but all I could find was the two Maxims going 8:1 then 1:16. The main point is the idea of reducing the data and fanning it out to lower speeds to make it manageable.

I'm no expert, but I believe memory and glue logic would be minimal. The chips are not expensive-- just ADCs and demuxers. Demux the high speed video stream using simple clock division to a wider, slower path and record it. By skipping every other pixel at the start, and using half of that for the color channels (standard practice), you reduce the data to something that can fit over a PCI bus at a sustained rate with available technology.

Not true HD, and probably not much better than a DVD if at all, agreed. It is meant to be a simple example of what might be possible with minimal design work to record HD.

I've worked out encoding schemes as well, using multiple wavelet compression chips (Analog Devices ADV601 chips) in parallel, but getting that to work would be much harder. I'll post a separate RFC on that one when I get a chance.

-Benson
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post #6 of 16 Old 01-03-2002, 11:27 AM - Thread Starter
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I think calling this 960x540p is actually wrong. It is meant to timeshift 1080i, not do any de-interlacing. It should record the incoming 1080i signal and so it should output 1080i on playback. The playback quality will not be as good horizontally since pixels will be doubled in that direction since half were thrown out to make recording possible.

You could do the deinterlacing on playback if you wanted using the computer's CPU, but it I'm not sure if today's CPUs could handle it (essentially an HD version of dTV, and I'm not sure how close to the wall dTV is at SD).

You'd also need a VGA input on the target display or use a VGA-to-component converter since the likely playback mechanism would be the video card. Turning the bits back into pixels would require packing and YUV2RGB (unless there's a card that supports native YUV in the frame buffer), but I think that could be done with today's CPUs. Another advantage of recording uncompressed video, since if the data were compressed you'd need to decompress it, and that would definitely require external hardware. But the compressor chips I've looked at decompress as well in the opposite direction.

-Benson
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post #7 of 16 Old 01-03-2002, 11:27 AM
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Going through parallel to serial convertors will not reduce the data rate. If you are going to ignore every other pixel, that will make some awful looking video.

The reduce data, it must be filtered, the same way analog bandwidth is reduced. In fact the same equations apply, but rather than passing an analog signal through chokes and capacitors, you will be using multipliers and accumulators to do the math in real time with the video data. Don't look to DSP's yet at these speeds.

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post #8 of 16 Old 01-03-2002, 12:05 PM - Thread Starter
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Glimmie,

In response to your second post: the data reduction isn't done via the demux, it's done via throwing out every other pixel as it comes out of the ADC. The ADC itself demuxes the data from 3 video channels into 6 at half the rate-- you can take advantage of this and ignore one set of 3, reducing horizontal resolution by a factor of 2. Since most displays can't resolve 1920 pixels horizontally anyway I'm hoping this won't have a major impact. Note that in the case of the two color channels you aren't throwing anything away since the color channels are at half resolution in the original 4:2:0 digital stream sent to the receiver. Here's an attempt at simplification:

1) Original Y field: 1920 x 540. 1920 x 540 unique pixels. Target: 960 x 540.
2) Original Pb,Pr fields: 1920 x 540. 960 x 270 unique pixels (assuming 4:2:0). Target: 480 x 540.

Further data reduction is done by sampling the color channels at half again horizontally (to get 480x540 above). I would prefer instead to remove the color information in the vertical direction, since that is where the redundancy lies, but that would add complexity since it would require knowing what line you are one and remove the purely serial manner in which the stream is treated.

Glimmie, you're right that simply doubling on playback (as I said in my previous post) would be unacceptable now that I think about it. That's probably why I originally thought of this as 960x540p. Perhaps the CPU could make something look good on playback, either by deinterlacing or filtering as you suggest. Any ideas? We need to be sure to output 1080i at the end, though, since that's what the display was expecting from the source.

The demux part gives you breathing room in the clock rate department and lets you use parallel digital capture cards. For instance, the max capture rate of the PCI-DIO-32HS is around 20 MHz, but can simultaneously capture 32 bits at that rate. That puts it above Firewire (600 Mbps vs 400 for Firewire) and is the fastest track into the PC that I know of, though it might be a little close to the edge and the card is expensive. I wish I could find that Rockwell chip (it used to be on rsc.rockwell.com) because it reduces complexity and gets you down to a 4.64.. MHz capture rate for a 128-bit wide path. But I think this is probably beyond a set of parallel ports doing DMA in ECP mode. Anyone know?

-Benson
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post #9 of 16 Old 01-03-2002, 01:44 PM
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I think the major question here is how are you going to store the data? You will need 3/4 of a terabyte just to hold an average movie with some buffer space. Off loading this to data tape would be very time consuming and expensive.

This all sounds like a good engineering exercise to test these new parts but I don't see any practical use for such a device based on the storage problem.

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post #10 of 16 Old 01-03-2002, 02:16 PM
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Maybe way off base here, but how similar is a single connection (R,G,or B) of an RGB signal to an s-video signal. Would it be possible to record even one color of say a 480p signal using an BT878A capture card and some simple adapter? I though some of those cards could reach 480p now, but I'm not an electronic chip expert.

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post #11 of 16 Old 01-03-2002, 04:32 PM
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Quote:
Originally posted by trbarry
Maybe way off base here, but how similar is a single connection (R,G,or B) of an RGB signal to an s-video signal. Would it be possible to record even one color of say a 480p signal using an BT878A capture card and some simple adapter? I though some of those cards could reach 480p now, but I'm not an electronic chip expert.

- Tom
Well in theory that would work but you still have a huge storage issue. It's just now spread across three PC's.

We have an uncompressed HDTV disk recorder where I work made by Sierra Design Labs (now owned by Davinci Systems). This device actually does what you propose. It is four STDV disk recorders combined through a demultiplexer and played back through multiplexer. In fact they can be split up into four SDTV systems if you wish. In HDTV the four drive arrays store Yodd, Yeven, pB, and pR respectivily. This thing holds an hour of uncompressed 1080i. We never use it as a simple storage device though, that would be a waste when we have tape machines and lightly compressed disk machines. It's main purpose is to download and upload HDTV special effects from computer systems that cannot deal with HDTV in real time.

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post #12 of 16 Old 01-03-2002, 05:54 PM
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Quote:
Well in theory that would work but you still have a huge storage issue. It's just now spread across three PC's.
Actually I was thinking about 3 PC capture cards, not PC's. I think some STB's can output 480p, right? And the next release of DScaler will maybe handle multiple cards. But I'm still not sure about cards capturing 480p.

But say you used 480p and captured it at DVD resolution of 720x480. Throw away the odd fields for recording at 30 fps, raw (progressive) RGB with 3 bytes/pixel.

Then every second you would capture 3 bytes * 30 frames * 720 * 480 = 31.1 MB / sec, or 111.97 GB / hour, potentially to 3 separate drives.

Now I recently picked up a 100 GB drive at Sam's Club for $119 after rebate. So give me a couple more of these and a few hours with Divx and a good P4 processor and I'd have at least a DVD quality movie using only current toys.

No wonder the MPAA worries about first run movies on HDTV.

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post #13 of 16 Old 01-04-2002, 10:26 AM
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But why go to all this trouble for DVD 480P quality? Just buy the DVD and run it through your progressive player. And typically the home video release is the first out even before PPV.

This is what is so absurd about the MPAA concerns regarding clear analog HDTV connections. Yes, it can be done but it's financially prohibitive.

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post #14 of 16 Old 01-04-2002, 11:10 AM
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Actually there is another issue I probably should not have glossed over. I've never seen a PC A/D capture card that didn't add a small but noticable amount of noise to the picture. I'm not sure I'd have any real reason that to believe that wouldn't be true also for component conversion.

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post #15 of 16 Old 01-04-2002, 05:44 PM
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Quote:
Originally posted by Glimmie
This is what is so absurd about the MPAA concerns regarding clear analog HDTV connections. Yes, it can be done but it's financially prohibitive.
You expect rational thought from the MPAA security committee (or whatever it's called)? :)

-- Mike Scott

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post #16 of 16 Old 01-05-2002, 07:38 AM
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Quote:
Originally posted by michaeltscott
You expect rational thought from the MPAA security committee (or whatever it's called)? :)
I believe that the correct phrase is Information and Control Nazis

HBO is guilty of Crimes Against Filmanity!

From Paragraph 44 of the 5th Report and Order: We note in this regard that broadcasters and networks have emphasized their commitment to high definition television.

Our
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