I have a
.wmv file that I am trying to upload to Vimeo. The resolution of the video is
1280 x 960, but Vimeo prefers
1280 x 720. How can I change the resolution of the video to meet this guideline?
It's a question of whether Vimeo prefers to have standard 720p video or if it will handle your existing source material just fine. If you can use what you have, use that. Re-encoding a video or changing its aspect ratio will always degrade its quality, and this might not be what you want.
If you want to change the resolution to match 720p, you have three options:
You can grab yourself a copy of free, open source and cross-platform Handbrake. Load your source file, and in the Picture Settings, change the output size. You will need to check the Anamorphic » Custom box to allow for other aspect ratios, and you can preview your video to make sure it looks how you want.
Finally, for re-encoding—something you'll have to do when changing the size—you may want to choose a low Rate Factor in the Video Quality preferences:
It's more or less a "quality knob". Lower values mean better quality, higher values mean lower quality. You should choose something between 19 and 24 depending on your source content and desired result.
I would recommend (for best results), using video editing software such as sony vegas, imove, windows movie maker, final cut, etc to trim the video to the res you want. in most more advanced editing solutions it is as simple as changing the output settings on the render.