Mac Daddy World

Following a continuing trend of adding new things without telling anyone, the recent QuickTime 7.2 update includes more than just bug fixes.
We’ve confirmed that the QTKit Capture functionality previously billed as a feature of Leopard is included with the update. (See the section on QuickTime Improvements.)

The fun new functionality is all there after updating to 7.2, but there are no new header files (no public API yet). Also, the functionality is now used by QuickTime Player Pro. However, you probably won’t notice much of a change except a little progress indicator in the Recording section of the prefs when it’s scanning for cameras, and hopefully a performance improvement.

Since it’s in the wild, I can now talk freely about this cool new feature of QuickTime. All of this I learned simply by hunting around and looking at sample traces of a running video stream in the new version of QuickTime Player.

QTKit Capture looks to be a total ground-up replacement of the Sequence Grabber. The Sequence Grabber is a very ancient part of QuickTime, designed long ago as the way to capture streaming audio/video. It doesn’t appear to be going away, but QTKit Capture doesn’t use it internally except for reverse compatibility* with old vdig drivers. Where the Sequence Grabber uses QuickDraw, QTKit Capture makes heavy use of Core Video and OpenGL. Also, the top layer is Objective-C so it can be integrated easily into a Cocoa app.

I’ve done some looking around and found some interesting things:

It makes use of some new private frameworks. New to the club are:
CoreMediaAuthoringPrivate.framework
CoreMediaIOServicesPrivate.framework
CoreMediaPrivate.framework

CoreMediaIOServicesPrivate’s framework Resources folder contains a number of plugin modules. There’s one for AVC (DV cams), IIDC (external iSight), and VDC (the built-in iSight). In a nutshell, CoreMedia appears to implement a Device Abstraction Layer (A way to allow access to all video devices without having to know the details of the device.)

Other notes:

• * QTKit Capture still works with existing QuickTime component vdig modules (macam still works). In this case, it is actually running the Sequence Grabber below CoreMedia. For the built-in iSight however, the Sequence Grabber is not being used. Hopefully, Apple will provide a new way to write plugins for third party devices so the SequenceGrabber doesn’t have to be used. However, they do support 3 major video camera standards (IIDC, AVC, and UVC), so device developers going forward would be wise to implement one of these standards, eliminating the need for writing their own driver.
• You can build and link against the new functionality if you have the proper header files.

This entry was posted on Friday, July 13th, 2007 at 4:20 pm and is filed under Cocoa, OS X, QuickTime. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.