For developers, instructors, podcasters and others who want to capture video from iOS devices, the current method of choice is to either use an external video camera aimed at the device's display, Apple's HDMI cable attached to a dedicated capture device, or a third-party Wi-Fi solution such as Reflector that can capture an AirPlay stream of a mirrored screen. Now Apple's going to make video capture much easier by allowing OS X Yosemite Macs to grab iOS 8 device video simply by connecting a Lightning cable between the two.
When the iOS 8 device is attached, it appears to the Mac as a video input source in QuickTime. QuickTime can then be used to capture the video coming in from the iOS 8 device. Although we're not sure at this time, you should also be able to use iMovie or Final Cut Pro X to receive the video stream.
Developers were given the word yesterday that the App Store will soon allow video previews, so this new capability will make it simpler for them to prepare the App Preview content for upload later this year.