optimal frame dimensions for DV video?

Discussion in 'Professional Video Production' started by liu, May 2, 2011.

  1. liu

    liu Guest

    http://www.flashsupport.com/books/fvst/files/tools/video_sizes.html
    I use this as reference but wonder if I need to take DV's non-square
    pixels into consideration when converting it for web deployment?
    so instead of using 432 x 288 (maintaining the same aspect ratio of
    720:480), I should change 288 to 320 (= 288*10/9) by taking the 0.9
    vertical ratio?
    Also is video dimensions should be multiples of 16 still important
    nowadays. If I have to stick with it, I have just a few frame
    dimensions to use.

    Thanks,
     
    liu, May 2, 2011
    #1
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  2. liu

    Frank Guest

    Nice chart but somewhat dated as encoding Flash video using either the
    On2 VP6 video codec or the Sorenson Spark video codec is a thing of
    the past. The Adobe Flash player has accepted files encoded with the
    ISO/IEC 14496-10 MPEG-4 Part 10 AVC / ITU-T Recommendation H.264 video
    codec (along with MPEG-4 ACC-LC audio) for several years now, and the
    file extension can be either .flv or .mp4, your choice.
    Yes, you do, unless you're posting raw DV files for consumption by a
    specially targeted audience.
    The square-pixel equivalent of NTSC video is 640 by 480. If you wish
    to use a smaller frame size, use 320 by 240. For truly
    postage-stamp-sized video, use 160 by 120.
    Different codecs have different requirements, and there are literally
    hundreds of video codecs in existence, although there are a few codecs
    which will produce frames of video of any arbitrary size. In general,
    if you stick to using frame sizes that correspond to those used for
    OTA (over-the-air) broadcast, or fractions thereof, you'll be okay.
    Hope this helps.
     
    Frank, May 2, 2011
    #2
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  3. liu

    liu Guest

    What is the math to get to these numbers? From my calculation.
    720 x 480 DV has 3:2 aspect ratio. Use that ratio on 640, it becomes:
    640 x 426.667. Then take the expand the v from 0.9 to 1, it becomes
    640 x 474.0741. Why is it 640 x 480 if I'd like to maintain the same
    aspect ratio?

    Thanks,
     
    liu, May 2, 2011
    #3
  4. liu

    Bob Myers Guest

    Right there is your problem. You are assuming "square" pixels for 720 x
    480, and that's not the case. 720 x 480 video is intended to be shown
    as either 4:3 or 16:9 (to determine which it is, you have to check a
    flag bit).

    Bob M.
     
    Bob Myers, May 2, 2011
    #4
  5. liu

    Frank Guest

    No mathematics, just simple arithmetic.

    Keep the 480 scan lines as is, but multiply the width by the pixel
    aspect ratio of 0.888889 to 1 (720 times 0.888889 equals approximately
    640).
    The correct calculation is as given above.
    Since NTSC video has a display aspect ratio of 4 to 3 (4:3), the goal
    isn't to maintain the storage aspect ratio but to convert to the
    display aspect ratio. There are various methods to accomplish this.
    Here's a recommendation that Adobe used to give:

    "Practically speaking, you should use the D1 resolution for videotape
    and DVD; use a 4 x 3 ratio for computer playback.
    A standard conversion from D1 to 4 x 3 would begin as follows:

    1. Capture at 720 x 480 pixels.
    2. Deinterlace or inverse-telecine the video.
    3. Crop eight pixels from the left and right sides (so it's 704 x
    480).
    4. Resize the video to 640 x 480 pixels."

    And here's a link to the original announcement (dated August 20, 2007)
    about AVC/AAC support in Adobe Flash Player.

    kaourantin.net: What just happened to video on the web?
    http://www.kaourantin.net/2007/08/what-just-happened-to-video-on-web_20.html
    HTH.
     
    Frank, May 2, 2011
    #5
  6. liu

    liu Guest

    Thank you so much for the helpful information, Frank and Bob.
     
    liu, May 3, 2011
    #6
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