Cocoa Is My Girlfriend

I am currently working on an application that needs to set markers in audio and video tracks. While it’s easy to find a marker visually in the video tracks, it wasn’t quite so clear as to how to set a marker in an audio track. In this tutorial, I’ll demonstrate how to create an audio scrub utility that will play a short audio clip when you drag an NSSlider. It shows the current time code of the track while you update the slider.
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In my first post I wrote about using NSOperation to grab an image of the current frame of a QuickTime movie while it was playing and save it out to the filesystem. Considering the excitement that is surrounding Core Animation these days, I thought it might be interesting to take that project and change it to instead grab the current frame and animate it across the screen using a Core Animation layer (CALayer). I had to employ a few tricks to get it to work, but the end result, while completely useless, is quite excellent.

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Forget Mandelbrot sets (Apple coding headstarts) and Expression Trees. NSOperation is really not that hard.

In his post, Marcus introduced how to use NSOperation to greatly simplify multi-threading tasks in your application. I am now going to provide a step-by-step walk-through sample application that uses NSOperation, NSOperationQueue, and QTKit.

While looking around the Internet, I noticed that the only examples of using NSOperation available were related to scientific applications. I wanted something that I could relate to a little better and since I’ve been working with QTKit a lot lately, I figured it would be a good framework to build from. This application simply grabs images of a movie while it is playing back and saves them out to a file. It’s pretty simple, but it shows how to do something fairly practical.
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