iMovie HD. Wierd.

MacTruck

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Jan 27, 2005
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So I import a movie from my sony handycam using firewire. Its now in iMovieHD. It looks nice. Now I export to DV file and it is stretched a bit and it looks dull. I even opened the imovieHD project folder up and opened the dv file in quicktime and it looks just as bad. Why does iMovie HD show it ok but the file sucks?
 

MacTruck

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stoid said:
As far as the stretching goes:

The DV standard and therefore DV stream format iMovie imports to are 720x480. However, on playback, the image is reproduced with essentially non-square pixels at 640x480.

When you say playback you mean in iMovieHD or in quicktime?
 

pdpfilms

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Jun 29, 2004
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Vermontana
I'll tell you right now I have never understood square and rectangular pixels, no matter how hard I try. All I know is you produce the movie in one form, and it's (almost always) automatically transformed into the other for TV format.
 

The Truth

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Feb 23, 2005
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TV uses weird shaped pixels but computers use square pixels so when you replicate a TV image pixel for pixel on the computer screen it looks stretched. You can adjust the shape of it easily enough if you have quicktime pro in "Show movie properties". I can't tell you the exact figures it should be for NTSC but I know you need to convert PAL from 720x576 to 768x576. Sorry if this is absolutely no help.
 

Makosuke

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Aug 15, 2001
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The Cool Part of CA, USA
Short answer: It's too wide when you view it in QT Player because QT Player doesn't automatically make it a 4:3 width:height ratio like iMovie does. If you rescale it to 640X480 or some other 4:3 ratio size, it'll look correct. The color shift is almost certainly due to how QT Player draws the video on screen, and is probably related to it not deinterlacing the video for you. It can do this, though I'm not sure if you need QT Pro for it--it's buried somewhere in the options. Try opening the video in VLC and turning on deinterlacing.

Long Answer:

The stretched thing is as others said. A standard NTSC TV has (in theory, though there's a lot of variation that I don't clearly understand) 720 collumns by 480 rows of pixels that it draws every 29.97 seconds in two passes (that's interlacing--it draws every other horizontal row, then starts over and fills in the blanks, so you really have 60 720 by 240 images every second).

Standard DV video, which is what iMovie uses, is exactly this format--720 by 480 pixels, 30 (ok, 29.97) interlaced frames per second.

Since a standard TV has a width-to-height ratio of 4:3, the pixels aren't square--they're a little taller than they are wide. You can actually see this if you get really close to your TV screen--you'll see little vertical color stripes that make up the pixels, and they're slightly rectangular instead of square.

Computer monitors use a much simpler and more logical system; pixels are always square, and there's no interlacing--it just draws one whole frame then another.

The problem with this is when you open a 720X480 non-square pixel interlaced image in a computer player, it looks funny; it's too wide (the pixels should be horizontally "squashed" but they're not) and since your monitor refreshes MUCH faster than a TV you can actually see the interlacing lines. This is likely the problem. iMovie compensates for all of this automatically--it de-interlaces the image and forces it into the correct aspect ratio so it looks good while editing.