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Dropped Frames in DV

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  • #16
    Canopus has received, and will continue to receive kudos for having been first out of the gate in this 1394 DV NLE saga, and for apparently staffing themselves with some programmers who are worth their salt.

    However, you're right about this all being about the software, dgcom! It's a big reality adjustment for the NLE market to break away from the hardware based 'system', since the hardware codec has moved out of the computer and into the camcorder. A lot of people still haven't quite realized what this means. It's here. It's here NOW: DV camcorders have their own 'capture card' built in. IEEE-1394 ('firewire' or 'iLink') is simply a new style of serial port... very inexpensive.

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    • #17
      ok, i saw above a ? of when to use 29.87, and when to use 30 fps... color ntfs is always 29.97, black and white is always 30.
      another way to solve your problem, is just to edit and output the file in the same fps that you captured it in.... ie: if your card captured at 29.97 fps, don't edit and output at 30, you're just setting yourself up for trouble.

      my $0.02

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      • #18
        How do you disable "write behind cache"?? In the system files area, there is something calle read-ahead optimization with an adjustment bas pulled all the way to the right...is this it????

        thnks

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        • #19
          How do you disable "write behind cache"?? In the system files area, there is something calle read-ahead optimization with an adjustment bas pulled all the way to the right...is this it????

          Bongo: It's in the 'troubleshooting' tab of that same area where you found the read ahead optimization slider, it's a checkbox that lets you disable it.

          Keith: It's true that the DVRaptor has been the real star of the show for quite some time, now. One drawback of the cheap route is still that you have to tweak around a bit to get eveyrthing to work right. Also, it's still limited to the filesize (no timeline playback yet).

          Hippie91 & Serengeti: what the heck are you guys talking about????

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          • #20
            We're talking about the NTSC television electrical signal, and the different frame rates that are commonly used for it, and a little technical info to boot (not a lot though, Im no engineer )

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            • #21
              Serengeti

              If you are in Tanzania, as is plain , you may not know but the frame rates in both USA and Europe were based at 1/2 power frequency so that, in the days when power smoothing was less perfected than it is today at both the Tx and Rx ends, there were no annoying hum bars moving up and down the screen. In fact, the power frequency could vary and the Tx end line frequency was always kept at a multiple of the momentary power frequency to give the required number of lines. As the power within a given country was generally on a nation-wide grid, this meant that the image was stable from start to finish. Hence the nominal frame rate was 25 Hz in Europe and 30 Hz in the USA. As technology advanced, so these frequencies actually became fixed and were divorced from the real power frequency. So monochrome TV in the States WAS, as was stated, at 30,000 Hz. The CCIR standard still quotes 30 Hz but the FCC standard actually normalises the horizontal scan frequency only for colour TV at 15 734,264 Hz +/- 0,044 Hz, this being 2/455 of the chrominance subcarrier frequency, which is fixed at 3,579545 MHz on the upper sideband (don't ask me why!). If you divide 15 734,264 by your 525 lines, this gives a frequency of 29,97 frames/s. The same standard specifically quotes 15 750 Hz for the line frequency and 60 Hz for the field frequency for monchrome transmissions, because there is no chrominance subcarrier to which it can refer.

              In summary, 30 for mono and 29,97 for colour is an internal US FCC standard and 30 for both is the international CCIR one. Of course, this is dictated from the Tx end and I doubt whether camcorders can guarantee a tolerance better than, say, +/-0,05 Hz, anyway. I use PAL, which does not have this problem, and I have had, from a good camera, frame rates varying from 24,96 to 25,02, which ain't bad for stability in the playback of a relatively elastic tape. So, I would say, never expect a perfect frequency unless you are recording from a fully pro source, where the master subcarrier is generated by an oven-controlled quartz crystal cut for minimum TC.

              ------------------
              Brian (the terrible)

              Brian (the devil incarnate)

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              • #22
                GREAT. Thanks alot, Brian. Jeez. Way to make a conversation WAYYYY too technical!!!




                Actually, that was very informative.

                Im not sure if you clarified a concern of mine, though... considering the change of frame rate, do TV stations _ever_ broadcast B&W (anymore)? I'd assume not, since they time their signal on 29.97.

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                • #23
                  You know, DV is VERY constrained format...

                  DVSD (DV standard definition) is:
                  - NTSC 720x480 29.97 fps
                  - PAL 720x576 25 fps

                  It's almot not possible to change it during "capture" (which is just transfering data to HDD from tape, not Analog-to-Digital conversion).

                  Later, the fps can be changed in AVI/MOV file via editing software, but it won't change anything actually... And DV codecs won't produce anything different from those constraned settings.

                  That's much different from what was before about video capturing...

                  DGCom
                  DGCom

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                  • #24
                    Isn't there a feature on the XL-1 that allows you to record in progressive frames? I think the frame rate is 25. How does that fit into the CODEC, or is that some kind of crazy XL-1 Camera-only thing?

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                    • #25
                      It does not matter how you actually shoot your footage - 15 fps, 30 fps, film mode, interleaced, progressive...

                      There would be only one particular frame rate on tape (read - in DV stream), 25 fps PAL and 29.97 NTSC. Nothing else.

                      DGCom
                      DGCom

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                      • #26
                        Jeff b,
                        Write behind caching is the last button on the Troubleshooting tab of the File System Properties.
                        Michka
                        I am watching the TV and it's worthless.
                        If I switch it on it is even worse.

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