Difference between 720x480 and 640x480 DV import in iMovie?

Discussion in 'Digital Video' started by MD5Hash, Feb 27, 2011.

  1. MD5Hash macrumors member

    MD5Hash

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    #1
    I've run into this problem before, but I've yet to actually receive an explanation about this strange discrepancy between the size of the raw DV files that I can see in the Finder, versus what iMovie allows me to work with.

    My DV camcorder (north america) NTSC camera apparently is shooting at 720x480 and I have iMovie set to import at full resolution from the camera. I see the files are 720x480 in .dv format, but yet when I go to export the videos into MOV or MP4/h.264 formats, it only gives me the option to output at the "current" resolution or lower, of 640x480. I don't understand why there's this strange hangup with iMovie that isn't seeing that I imported the videos with an extra 80 pixels on the left and right sides!

    Can anyone either explain this here, or find the page I've (fruitlessly) searched for on the internet that explains this? Or is iMovie just junk and I should stick to Adobe Premiere Pro? I hate this iMovie interface since the 2006 version, but my Mac is faster than my PC with Premiere on it, so, there you have it...
     
  2. MisterMe macrumors G4

    MisterMe

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  3. MD5Hash thread starter macrumors member

    MD5Hash

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    #3
    Yes, I did that. It says that the current resolution of the file is 640x480 and that's the option it gives me. What I'm saying is that I know for a fact my camera exports at 720x480, I'm working on it in Win7 at this moment and the avi files I see here (dv encapsulated) and they're also 720x480. So export using quicktime isn't the problem here, it's that the entire iMovie program is for some reason trying to force the working resolution of my project to 640x480 and is not allowing me to modify that.
     
  4. LethalWolfe macrumors G3

    LethalWolfe

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    #4
    I don't use iMovie so I can't say why it's doing that, but the difference between 720x480 and 640x480 is the difference between square pixels and unsquare pixels. Long story short computers always use square pixels where as some formats of video use unsquare pixels. A properly displayed 720x480 image on a computer screen will look the same as a 640x480 image. I say "properly displayed" because if the program doing the displaying doesn't understand unsquare pixels and how to properly interpret them it will display the 720x480 image slightly distorted.


    Lethal
     
  5. xStep macrumors 68000

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    #5
    You have confirmed that on both Mac and Windows that your DV files are 720x480. That is as expected as that is what comes out of NTSC DV cameras.

    When editing on a computer, the editor converts that on the fly to 640x480 to account for the aspect ratio. If it didn't, you'd see a wider (fatter) picture that wouldn't look like as it would if played on your 4:3 picture tube TV.

    When you export, iMovie believes you want to keep the aspect ratio correct so that the picture looks nice. You can override that by using the QuickTime Export options and customizing the width and height. See my iMovie Export Guide which may help you with how to use that feature. You can also export DV format with that option.


    The older iMovie HD had a feature that allowed you to write back to a DV tape via the firewire connection. What it writes back is a 720x480 picture for NTSC.

    P.S. You didn't say which version of iMovie you are using. That information is often helpful.
     
  6. MD5Hash thread starter macrumors member

    MD5Hash

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    #6
    thanks for the heads up guys :) i didn't realize that's what it was but I found that option for 'overriding' the system to 720x480 20 minutes ago and am now exporting the file to MP4 right now. says it will be 2 hours. Hopefully the 720x480 output file will look good in Windows Media Player, Quicktime, and VLC (the three platforms I need it for). None of these files will ever see an old 4:3 TV, I hope :p As always, I find myself Apple gave me more manual controls for the file input preferences (although I'm quite pleased with their export to quicktime output options).

    If you don't mind a second question, does anyone know why it doesn't push the processor to its full limits? my core 2 duo mid-2010 macbook pro (2.4ghz) is only at 78% proc usage right now. As long as I don't have any other programs open (I'm typing this from my PC) shouldn't it be hitting 100% usage for best efficiency?

    (iMovie 2011, sorry!)
     
  7. xStep macrumors 68000

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    #7
    For computers you want to export to 640x480 otherwise things will look wider than they should be.


    The system is made up of many parts. If the CPU isn't consistently at 100% during a video rendering, there maybe a bottleneck somewhere else; drive, memory speed, bus speed, GPU, etc.
     
  8. martinX macrumors 6502a

    martinX

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    #8
    720 x 480 is the DV NTSC standard. It records non-square pixels for display on a 4:3 aspect ratio display (i.e a standard definition non-widescreen TV).

    Computer monitors have square pixels.

    NLEs and software players recognise this and map them accordingly on-the-fly. By exporting to 640 x 480 (square pixels) you will have mapped the pixel aspect ratio correctly.

    For the record I hate the following:
    • non-square pixels
    • interlacing
    • NTSC and those dumb frame rates. 29.97? Really? Just go PAL and use 25 then you won't be sweating about trying to get the "film look" of 24fps from doing pulldown stuff on your 30 fps (sorry, I meant 29.97 fps) shots
     

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