Indie Film Live

Saturday, January 07, 2006

Technical_01: Cables and Storage

Here it comes, Ladies and Gentlemen…

Finally the Atomic VFX guys have started posting something.
If it is useful – great, if it is not useful or
something in your opinion not true – post a comment please.

Storage:
Statistically speaking if you want to make a 100 minute movie, you shoot about 700. Not true anymore. Now it is all digital. Our last “Test Shoot – Day 1” showed that we end up shooting a lot more just because we can… We can view footage on set straight away. If a director isn’t happy, no problem: let’s just have another take. And VT roll before camera, say up to 5 seconds - that is 150MB of wasted space, just like that. If this were uncompressed, it would be 1.1GB. Thank goodness for “CineForm” mathematics and support. Without them and with our independent budget, this project would never have kicked off from the start line.
In our case we will have a few shoots with special visual effects and some of them may be so important that we want them to be uncompressed anyway. For this we need at least 4 SATAII 7200rpm drives. However the motherboard must have SATAII support and all four drives must have the “3Gb/s” switch enabled. Stripe them together and “Hitachi” HDS725050KLA360 model will give 224MB/s. This just makes it - for real uncompressed we need 221MB/s. But hold your horses; “Wafian” is planning to release a software update with uncompressed capture ability (to RAM with 24p extraction option). This means that we don’t need unsecured RAID0 configuration and we can stick to the RAID10 that is on the “Wafian” already. If we plan our shoots carefully, we will have the entire movie on each box (930GB is about 9 hours of “CineForm” footage).

Cables:
Yes cables, not satellite transmission. With 221MB/s from component output of “JVC” GY-HD100E camcorder, it is still too expensive to transmit data wirelessly. So we decided to use normal off-the-shelf coaxial cable. When we started there was no component capture card on the market, so we used “AJA’s” HD10A HD-SDI converter and captured the feed from that. “Wafian” now have a “AJA’s” video capture card with component input that saves us having to use the extra conversion. We can now take the feed directly from the camera into the ingest box. What I discovered is that digital data requires very expensive cables to transmit over long distances: with SMPTE292 cable the maximum distance will be under 26 meters. Over that length the capacitance and resistance of the cable starts filtering out the higher harmonics of the digital signal. This results in the digital square wave becoming rounded and ultimately impossible to read accurately. The analog signal from the component output can run much further because it does not contain the high harmonics of the digital signal. But the analog signal can easily pick up external junk like electromagnetic interference from the generator. Such a sensitive cable is better to pull last and take away first and run over 20cm away from any power cables on the floor. However, it is still easier to pull 30 meters of cable to the camera on the middle of the set rather than moving the entire VT system closer to the camera.
The most important factor that we found on set is the quality of the cable itself. Don’t save money on things that are cheap anyway. We used two sets of the cable, flexible and non-flexible… Non-flexible breaks too easily, after 3 hours of heavy usage only.

3 Comments:

  • Of course at CineForm we want remove any need for an uncompressed workflow. One of the reasons we want the Wafian HR-1 box to have an uncompressed mode is for simple compressed to uncompressed workflow comparisons -- to help prove uncompressed is unnecessary. If in 99.5% of shooting cases the image is indistinguishable we want to know what we can do to close that 0.5% gap. The recently added custom capture modes allows Prospect HD and the HR-1 to have the compression quality easily modified. Once the uncompressed mode of the HR-1 is running I look forward to the feedback so we help you not need that mode.

    By Blogger David, at 10:20 AM  

  • For you cable problems, have you guys looked at this:

    Telecast Fibre Rattler

    You can use the AJA analog/digital converter you already have, and then use the Rattler to run fibre runs instead of 75 Ohm cable (which as you've noted can't go to far).

    Military-grade fibre can go a long, long way (Telecast says their device is good for 30Km!) and be run over by a car, truck, etc. without any damage.

    Might be worthwhile if you're having problems with cable-runs, and want to simplfy things by keeping your recording box in one location and then taking the camera wherever you want.

    By Anonymous Jason Rodriguez, at 10:08 PM  

  • Good Day Jason,

    I've never seen this specific converter but our main issue is BUDGET... Although extra gear may help it adds other problems such as signal conversion and electronic equipment problems. In our case 30m of cable is enough and also eliminates alternative (unforeseen) variables.

    Thanks for the link I will definitely keep this one in mind for future reference.

    By Blogger Pavel, at 5:48 AM  

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