Imovies "strobe" effect with AVCHD

Discussion in 'Digital Video' started by Koen007, Aug 3, 2008.

  1. Koen007 macrumors newbie

    May 19, 2008
    I have noted a certain strobe effect with a slightly fast moving camera or image. The effect is not visible when the image of video camera is shown directly an a television. I suppose therefore that it is a hardware/software problem of Apple.

    The computer I have is Imac 24" with 2800 hz and 4GB of memory.

    The camera is a Panasonic HDC-SD5.

    Anyone have the same problem or found a solution.

    According to the Apple shop the situation is normal because it is very difficult to convert avchd files ...
  2. Courtaj macrumors 6502a


    Jul 3, 2008
    Edinburgh, U.K.
    1. Are you using iMovie? Which version?
    2. By "strobing" do you mean jerky movement?
    3. When do you notice this? In the preview window of your NLE or once you've outputted (e.g., as a Quicktime movie)? If it's after you've outputted, what conversion settings are you using?
    4. Does this happen regardless of the shutter speed you have used?

    My experience with using an SD5 & iMovie is that I've not had any problem with jerky vision unless using a shutter speed of 1/25 (1/30 if you're in the US).

    There should be no issue with AVCHD on your iMac - I'm assuming it's an Intel Core 2 Duo. Whoever told you at the shop that AVCHD is difficult to convert is being willfully obscure since it isn't difficult to convert, just time-consuming (depending on the speed of your machine). However, quick pans and very fast movement can be a problem in AVHCD (just as they can be in HDV or any highly compressed video format).

    More info (as per the questions above) would help with the diagnosis though.
  3. Koen007 thread starter macrumors newbie

    May 19, 2008

    thanks for your support.

    Here are the replies to your questions :

    1. I use I movie08, version 7.1.4
    2 By strobe effect I mean that if the camera moves fast (in order to have a more non static effect), one can see clearly the subsequence of frames and there is not a continuous video effect.
    3. The effect is noticed when the video is imported as an event (both in the highest mode (1920/1200) as in the lower mode), when the project has been made, and also when export in as high quality in quick time.
    4. About camera shutter speed, I am not sure, but the video is recorded in the higherst mode (HG1920 is indicated in the menu of the camera (European version) . alternative modes are HN1440 and HE1440.

    I affirm your assumption about the computer processor type.
  4. Courtaj macrumors 6502a


    Jul 3, 2008
    Edinburgh, U.K.
    Okay, well without seeing an example, it sounds like you're panning too fast. Video employing inter-frame compression (e.g., AVCHD or HDV) will not cope particularly well with fast pans. Not much you can do about it, I'm afraid. Even a faster shutter speed won't help (can in fact make it even more apparent by reducing the amount of blurring).

    It seems odd that the issue is not apparent on a television screen. Is it a plasma or a CRT? High definition video will often look pretty bogus while you're working with it in the preview window of your editor, but if you deinterlace it upon export then much of the cringeworthiness should be ironed out.

    That issue aside, let's consider the more important issue of moving the camera quickly. I don't mean to preach, but as with any tool you need to work within its limits once you've established what they are. With most consumer camcorders, especially the highly-compressed high definition formats, that means panning slowly, avoiding scenes with complex motion, and avoiding fast cross-frame motion (i.e. objects entering at one side of the frame exiting at the other in less than a second) as much as possible. The SD5 records at 13Mb per second and at that level things like fast panning and side-to-side object motion are often too much of a challenge for such a camera.

    If you avoid these kinds of things, you'll be much happier with the quality of your pictures.

    Best of luck,

    P.S. The SD5 has excellent manual control of shutter speed and iris. Experiment with different manual exposure settings to see if you can find something that works better. All camcorders are more limited when used in auto mode only. Get to grips with manual exposure and you'll get more out of your videos.

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