Doing some research on recording NTSC digitally

Discussion in 'The Projects Forum' started by sstbrg, Sep 4, 2010.

  1. sstbrg

    Thread Starter Active Member

    Nov 29, 2008
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    I'm hoping to find a rather simple and cheap solution to capture, compress and record a NTSC video input.

    I'll probably be using ADV7180 for capturing a NTSC signal and converting it to 8bit YCrCb.
    I'm hoping to use a FPGA for compression and as a storage controller for a fast SD card. I guess the design will also require several RAMs, maybe other ICs I haven't thought about...

    I'm fairly new with video and just started researching this field, so any tips you can throw at me will be a huge help. Am I in the right direction here? Should I use a dedicated IC for the compression? Are there any development kits to help me out?
     
  2. tom66

    Senior Member

    May 9, 2009
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    You should probably consider using a dedicated video compression system.

    Using an FPGA is going to mean considerable time and money spent on trying to make an MPEG (or whatever you want) encoder to fit into an FPGA.
     
  3. sstbrg

    Thread Starter Active Member

    Nov 29, 2008
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    Yeah I did some more research, and it's a huge huge investment of time to code an MPEG (or other) encoder, may take quite a long time.

    So I'm looking into dedicated compression ICs - any help with that will be welcome. I'm planning to place it between the video decoder and the FPGA. Hopefully, most of the time will go into writing the encapsulation and storage controller for the Virtex FPGA. I may use large SD cards for recording (may as well be tens of GB), so storage space isn't really a huge problem.
     
  4. tom66

    Senior Member

    May 9, 2009
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    Well, you can get processors like the TI DaVinci, which AFAIK can assist with encoding video. But they are about $69/ea.
     
  5. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Don't forget Conexant, they were one of the first to make the chips used on the early TV cards you could add to your PC and turn it into a DVR and I believe to this day they're still very active in this technology.
     
  6. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Wouldn´t it be easier to use some microprocessor, instead of FPGA? I know you can use some processor core on it, but dedicated processor seems more up to the task. Writing such complex thing in VHDL doesn´t seem too good, but using some ready-made C routines and porting them for the processor could make the development time much shorter. What is the sampling frequency going to be?
     
  7. marshallf3

    Well-Known Member

    Jul 26, 2010
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    NTSC (or PAL or anything television related) involves some very, very complex waveforms. If you were able to reduce the vertical size of your television picture you'd see some bands running across the black areas that's full of all sorts of data - some used by the broadcasters, some by the receivers and some by both.

    You must also remember that a television picture is an amplitude modulated analog signal most of the time no matter how it's broadcast. We can convert this into digital in many areas now but not everywhere.

    http://en.wikipedia.org/wiki/How_television_works

    It would be most cost effective in his project to take advantage of any and all specialized circuitry that's already been developed.

    In all honesty I capture, compress and record NTSC signals through the use of a $60 plug in card in one of my home computers. It receives the signal off the air (as ATSC or NTSC) or from a choice of auxilliary inputs and ouputs it in digital format as any number of different file formats. If it's something I don't need or want absolutely the best clarity of I'll generally let the card output the signal as an .avi file, the compression level of which can be controlled. I've found that I get rather good quality at a 5 or 6:1 compression rate.
     
  8. sstbrg

    Thread Starter Active Member

    Nov 29, 2008
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    marshallf3, yeah, decoding that video signal is a project in its own. My goal is to record the video as, let's say a .mpeg file, on some SD card and play it in a normal windows media player. So I don't mind using any dedicated chips to aid in this process.
    Oh, and may I know what plug-in card are you using?

    Thanks for the tips so far, I might not give up on this project just yet :D
     
  9. marshallf3

    Well-Known Member

    Jul 26, 2010
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    When I looked behind the machine that handles video playback I've actually got two. One is a Norwood (CompUSA generic brand) and the other I caught on sale at NewEgg (It really pays to subscribe to their newsletters) a while back because it will do 1080i and most cable systems, many of which still broadcast in the NTSC standard so it's fully compatible.

    Go to: http://www.newegg.com and type hvr-1250 into the search box, they'll show two models. Mine is the second one, seems I liked it better for some reason.

    Seems to have come down in price a couple of times since I bought mine, $50 and free shipping will get you one but tomorrow is the last day of the sale.
     
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