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720p25 over 60p (Varicam)

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  • #46
    Plug and Pray? :)
    Steve
    EDIUS Trainer, Grass Cutter Gold
    A proud EDIUS EDITOR
    For more information on the Grass Cutter program please visit: http://www.grass-cutters.net

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    • #47
      Well we're buying a full copy of Edius 4.5 Broadcast today, so we're commited I guess.

      Fun times ahead.

      Edited:
      And here it is... Now I have a fancy box and all. Choice.
      Last edited by Sycophant; 10-18-2007, 12:35 AM.

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      • #48
        Originally posted by GrassValley_BH View Post
        True, it's insanely difficult to run magnetic tape as a non-constant speed. Too much mechanics involved to get it reliable and affordable.

        Ahh, okay, I figured out my confusion...

        The variable frame rate function is supposed to allow for blur/slow effects, but even the operating instructions don't really tell you what to do with it after it's on tape. Weird.
        Some clarification here. The Varicam does indeed record at a constant 60fps. If the frame rate is set to 25fps for example it simply flags the active frames. This flag is carried in the vertical interval data. The reason for this system, is as suggested, it is very difficult to vary the speed of tape in a helical scan recording system. With the advent of solid state recording that Panasonic introduced in the AG-HVX200 it is now possible of course to only record the active (native) frames and this would be called 25pn for example.

        Originally with the Varicam you used to use a device called a Frame Rate Converter. This box contained a hard drive with HD-SDI I/O. It would recognize the active "flagged" frames in the incoming signal and buffer them through the hard drive and then play them out at the correct frame rate.
        More recently NLE's such as Avid, FCP and Edius have incorporated this flagged frame recognition and perform the extraction automatically. Thus when I tested a 25fps Varicam ingest on a 25 Frame timeline I am getting realtime playback. If I had recorded at 50fps and I placed that on a 25 frame timeline I would have very smooth half speed. Also the newer DVCPRO HD decks such as the AJ-HD1700 and AJ-HD1400 have the ability to decode "on-speed" frame rates such as 30fps, 25fps and 24fps.

        The issue that Dylan is facing is that the NLE's will not accept a firewire input at 60Hz, they only accept it at 59.94, this is a .001 frequency difference and should be negligible. The other alternative is to ingest via HD-SDI via a Black Magic or AJA Kona card etc. These boards also support the variable frame rate function.

        I hope that this helps clear things up a little.

        Rick Haywood
        Manager Broadcast & Display Systems
        Panasonic New Zealand Ltd.

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        • #49
          Further to what Rick is saying... The issues with most NLEs for PAL users is the disparity between the 59.94/60Hz operating frequency of the deck and the 50Hz based framerates the applications are working with in PAL framerates.

          As for the constant 60fps - it is indeed recording 60 images per second to a tape, but as I said before, only a certain number are unique - only the flagged frames. In 25fps, the camera samples the sensor 25 times a second and records that frame to tape. Essentially you get frame 1 recorded for 2 frames, frame 2 recorded for the next three frames, frame 3 recorded for 2 frames, etc... The first frame with each unique image is 'flagged'. To rebuild the recorded framerate, only the flagged images are captured.

          The big bonus of Edius for me here is that it can capture the PAL framerates from the 59.94Hz deck over Firewire directly. Something that Avid and FCP are unable to do.

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