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Working with screen movies in iMovie Apps
If you're using iMovie to create screencasts, e.g. for software demos, there are a couple of things to know to get the best quality.

When you import source videos, iMovie seems to resample them to it's own internal resolution, so resampling on import followed by resampling on export can cause a substantial loss in quality and produce lossy videos full of artifacts.

The main trick is to choose the resolution of the input videos (screen captures) carefully. Depending on the video format you select when you create a new project, iMovie will work at different resolutions:
  1. DV: 720x480
  2. DV Widescreen: 853x480
  3. HDV 1080i: 1920x1080
  4. HDV 720p: 1280x720
  5. MPEG-4: 640x480?
If your input files match the project resolution, there'll be no need for it to resample.

Personally, I found that none of these were suitable for screen captures, so I set iMovie to HDV 1080i and used exactly half of 1920x1080, i.e. 960x580. Quality isn't perfect, but it's still better than some random other size.

When exporting, you need to be careful to set the export size the same as the capture size, 960x580 in my case. Go to QuickTime Export -> Expert Settings -> Options -> Size.

A couple of other notes: I also set the framerates of the inputs and exports the same; I'm not sure if this makes a difference. For the input, I use no compression or as lossless as possible compression (the Animation codec is supposed to be good for screen captures). For output, the H.264 codec seems ok. All the masses of codecs and settings are very complicated -- I think spending some time trying out different ones is the only way.

So in summary, though iMovie's a great tool for editing, it's obviously designed more for working with 'proper' video than screencasts, and you have to do some work to get suitable quality.

[robg adds: I realize this hint is quite general, but I'm hoping it prompts some comments on properly capturing and using screen movies in iMovie. Hopefully, with the attached comments, this can evolve into an excellent hint on making great screen movies via iMovie. Feel free to post links to sites with more detail, of course. For instance, I found this page useful for understanding DV Widescreen.]
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Standard resolutions
Authored by: Swift on Jan 11, '07 09:27:01AM

You'll notice these resolutions throughout the TV (now the "imaging") industry. It all comes down to the fact that we design pictures, ultimately, to be played on dumb machines that can't understand any other formats. It's the digital equivalent of sprocket holes. The processor, bandwidth, all of the multitude of parameters of any digital image, can in fact be adjusted, but you keep them to standards so that you can play it on your HDTV or STV or iPod with video. But you can tweak the signal processing, within a narrow range, which is important.

Do some transcoding with ffmegx, the Swiss Army knife of digital video processors. It took a while to learn it, because I didn't understand the "standard formats" business. You need to make a DVD with a strict set of dimensions, bitrate and signal correction, or it just won't play.

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Working with screen movies in iMovie
Authored by: sd on Jan 18, '07 01:24:56PM

I think that DV is 720 x 576



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