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Iain Buchanan <iaindb <at> netspace.net.au> writes: |
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> |
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> Neil Bothwick wrote: |
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> > On Tue, 16 Sep 2008 06:40:11 -0700, Grant wrote: |
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> > |
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> >> I think USB cameras would be the way to go. Does anyone know of a USB |
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> >> camera that works well with Gentoo? |
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> > |
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> > You can also use standard composite output security cameras, connected to |
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> > a TV card with a composite input. |
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> |
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> except that you then have to provide power to the camera as well, and |
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> composite is pretty bad at interference over long distances, especially |
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> if you're running AC next to it! |
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> |
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RG59 coax cable can be problematic, but should work to at least 900 ft. |
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RG6 is better (steel coated with copper in the coax core) that RG9. |
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Power runs, particularly AC are OK to cross (perpendicular) but shot |
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not be run parallel for more than a few feet. |
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|
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If the cameras use AC (many ntsc cameras do) then a single point of grounding |
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common for the AC power supply and the cameras is best. Sometimes isolation |
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devices and filters have to be used on either the coax, the power circuits |
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or both. RG6 cable should get you at least 1600 feet. |
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> On the other hand, I've run composite without amplification about 30 |
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> meters in a proper shielded environment, and had a clear (as the |
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> original) picture at the other end. I don't know how USB would go over |
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> that distance... |
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I do, I design and supervise commercial video installations for industrial |
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clients. |
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> USB cameras put the reliance on your webcam drivers working, composite |
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> cameras put the reliance on your TV card. And TV cards with multiple |
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> inputs can start to get expensive, but most cheap motherboards have |
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> multiple usb nowadays. |
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|
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QSee makes inexpensive cards that will perform 'frame grabbing'. |
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Before transmitting you have to *ENCODE* the video. The encoding process |
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is mathematically intensive (expensive) and runs best on a DSP such |
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as the 6000 series from TI or a FPGA that has a custom processor for |
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video processing implemented in hardware. |
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|
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Using a smoking 64 bit machine (Intel or AMD) will get you one to 2 channels |
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of real time encoding, at best. Now receiving H.264 or any other encoded |
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video stream and playing it back for viewing (mplayer, vlc mpeg4IP etc) |
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that's more reasonable. |
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This is the the best (cheapest) for hobbyist (webcams or ntsc(pal) |
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frame grabber boards for a (local) campus setting. If you are |
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going to re-transmit the video (stream it) over a WAN or the Internet |
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you've got a host of other issues to deal with. If this is the goal, |
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save yourself lots of grief and use H.264. |
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It's better that the finest system made/deployed by Pelco, Digital Micro, |
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GE or Honeywell ever dreamed of. Sure those big name systems have |
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billions of feature that *nobody* ever uses, but the quality or the |
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quality for a given amount of bandwidth you use; that war is over |
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H.264 has whipped all competitors, include what-ever-patented-wavelet |
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or anything thing else. I know, I've spent years deep in the mathematics |
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of these issues, put code on FPGA, and used dev kits from TI (Da Vinci) |
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and many others... |
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|
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H.264 rules and all other video encoding (although well intentioned) |
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drooles.... |
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|
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http://www.linuxjournal.com/article/9005 |
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http://www.balooga.com/mpeg4.php3 |
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http://en.wikipedia.org/wiki/H.264 |
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http://www.pixeltools.com/h264_paper.html |
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http://mpeg4ip.sourceforge.net/features/index.php |
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http://www.videolan.org/developers/x264.html |
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And if you really want to dive into video encoding, check |
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out this crazy Russian (actually a friend of mine). |
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http://wiki.elphel.com/index.php?title=Main_Page |
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Audrey has open source camera designs that run mjpeg or Ogg Theora. |
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James |