It looks like when I shoot video with UIImagePickerControllerQualityTypeMedium, on an iPod Touch it comes out 480x360, but on an iPhone 4 it's something higher (can't say just what as I don't have one handy at the moment) and on an iPad 2 presumably the same as the 4, if not something different again.
I'd like to shoot the same quality on all devices -- I have to add some frames and titles, and it'll make my life a lot easier if I just have to code that for one resolution. Is there any way to determine what the different UIImagePickerControllerQualityType values correspond to at run time? (Apart from shooting video with each and then examining the result, that is.)
Or is my only choice to use UIImagePickerControllerQualityType640x480?
If you need more customization/power on iOS than you get wish the higher level objects, such as UIImagePickerController, it is recommended to work at the next lower level: AV Foundation Framework. Apple has some excellent documentation on AV Foundation programming that should come in handy for that purpose.
Unfortunately, even there you are limited to capturing at 640x480 if you do want it standard across all devices. There, however, is a great chart available at the same link (but anchors are broken in the docs, so Ctrl+F to "Capturing Still Images") that lists all the resolutions for various devices under certain quality directives.
Your most solid bet, assuming 640x480 is too small, is to work out some sort of scaling algorithm that would allow you to scale according to the overall resolution.
来源：https://stackoverflow.com/questions/5795835/programmatically-determine-available-iphone-camera-resolutions