Staggering Video

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  • 07-22-2010, 06:51 PM
    Staggering Video

    I hope I can add to this forum one day - when I know what I'm doing!!

    How do you stop the video staggering when you are panning??

    I'm using a tripod and video head.

    I've tried several different modes, however, the result is the same. The video staggers and flickers as you watch the slow pan. I am using 24 frames / second

    Thanks, WilloW
  • 07-22-2010, 09:18 PM
    Re: Staggering Video
    try rendering the video to dvd or a lower quality file. I suspect that what you are describing is your computer struggling to playback the HD file
  • 07-22-2010, 09:25 PM
    Re: Staggering Video
    Hi Simon,

    60i plays back far more smoothly than does 30 frames and 24 frames outputted at the highest setting.

    Is there benefit in using 60i or should you stick to 24 frames which I believe is the standard?

    Will try your suggestion just the same.

    Just gave your idea a go exporting as a smaller movie. Once again 24 and 30 frames produced staggering whilst 60i was smooth as silk.

    Thanks S., WilloW
  • 07-23-2010, 01:25 AM
    Re: Staggering Video
    This is pretty good at explaining it

  • 07-25-2010, 04:02 PM
    Re: Staggering Video
    actually the standard in australia is based on the analogue pal (50i) and although the DVB-T standard will be completely phased in by 2013 when they are switching analogue off. one of the halmarks of the digital system is that it can play variable frame rates, although generally broadcasters are using 1080p with a frame rate of 25 for HD and 720i with a frame rate of 50 for SD, although the law says that they can call any broadcast of 720 or more HD! - don't get me started on how john howard fell for Kerry Packers glib presentation because he used cricket to show him the "new technology"

    But to answer your issue, with the interlacing, 60i your computer is actually working less hard as it only needs to display half the video at a given time, even if it does need to do that twice as often. displaying all the video fills up your GPU's memory and it "laggs" just a little bit. My slightly old but still purpose built edit suit does that now and then with full HD as well. As I am working more and more with HD I want to upgrade it but I have to justify the 5k+ price tag to the budget folks first.
  • 07-26-2010, 08:20 AM
    Re: Staggering Video

    Originally Posted by Skyman
    with the interlacing, 60i your computer is actually working less hard as it only needs to display half the video at a given time, even if it does need to do that twice as often.

    I'm still not clear on all the different video spec jargon, Skyman. Just to make sure I understand, 60i displays an interpolated 30 FPS by showing 2x interlaced? Do I have that right?
  • 07-26-2010, 12:19 PM
    Re: Staggering Video
    Interlaced, not necessarily interpolated.
    60i would be odd-numbered lines 30fps and even numbered lines 30fps, on alternate frames.
    So you see 60 frames, all with half the data, instead of shifting the full data 30 times a second.
    I know it adds up to the same thing, but with the architecture of some graphics cards a half-frame of data fits neatly in the memory where a full frame doesn't.
    When the data doesn't neatly fit into a single transfer, it gets messy (technical term) and you start shifting in blocks of data in the background and then enabling the whole frame once it's loaded.
    If your computer can't keep up then it doesn't redraw the whole frame before the next update comes in, and it starts staggering.
    Really comes down to how good your driver is, and how the hardware matches what you're trying to display, and even if your graphics card has a separate CPU or not (many don't) and if it uses system memory (cheap & nasty) or uses its own memory and fast bus.

    I did a bit of this in my past on the submarine/clinical imaging system and it used to make by head hurt trying to get it all out on an old 286/12 in 1/25 second.
    Going to a 386 was even slower, so some hardware upgrades may not be your friend!
  • 07-26-2010, 04:23 PM
    Re: Staggering Video
    Like Paul said, interpolated and interlaced are two different terms.

    Interpolated means (very roughly) that with pixel a and pixel b in any given image (still or video) the computer makes up pixel c between them to make the image bigger. or averages them together to make the image smaller.

    Interlacing is where video of a given frame rate is split up into lines that are sorted as odd or even, then displayed as a group so that only half the image need be displayed at any one time. It is as I said a throwback from Cathode Ray Tube televisions, but it is still used today as it can halve the amount of data required in a digital signal.

    Yes I know the same total amount of data is there, but if the processor takes extra time to process the extra data splitting it up into manageable chunks can really help.

    In this particular case, the camera is using the fact that by interlacing the image (and only needing half the resolution) its processors can handle 60 frames per second as opposed to 30. Incidentally this has a flow on effect to the computer which is struggling to display 30 full resolution frames but can easily display 60 half resolution frames.

    in photographic terms we are swapping 30 8mp fphotos for 60 4mp photos. Much the same as the digital slr's with the fastest burst rates have slightly less resolution to allow the cameras CPU to handle all the data.

    Again it links in with hard drive and computer bus technologies. with video sustaining the data rate is more important than short bursts of peak capacity followed by a lag.