Why do GarageBand, iMovie, Photobooth, and Hulu and Youtube videos slow down my whole computer?

Question

I have a higher end 13" MacBook Pro running OSX Snow Leopard 10.6.8 that I purchased in August of 2010. About a month ago, I was using iMovie to edit a project when all of a sudden it started responding extremely slowly. Like, near impossible to work on my project slow. The whole computer was lagging, the mouse was unresponsive and I could barely use the gestures on the trackpad to get to different programs. Eventually the pinwheel of death showed up, and I quit iMovie. As soon as it closed, everything returned to normal. I restarted the computer to see if that would help, but as soon as I opened iMovie again, the whole computer started lagging. I then noticed that the same problem occured when I used GarageBand, iPhoto, Skype, and when I watched Hulu or YouTube videos. With all of these programs/sites, everything is running fine beforehand, but when I open them up, chaos sets in. This problem doesn't occur when I use other intensive programs like Photoshop or Illustrator, nor while I'm browsing the web. The only web problems are when I watch a video. Any video. Other than that, web pages are as quick to load as ever, and I can use the computer normally for any other task. This is seriously a problem because I use iMovie and GarageBand for school a lot, and my grades depend on me being able to use these programs effectively. All of these problems have persisted with these apps since that first instance about a month ago, and no significant changes occurred to instigate them. In attempts to solve the situation, I have cleared my cache, freed up space on my drive (I have 56 free gigs out of 320), I have verified and repaired the disk permissions, and I have downloaded the Apple provided Trojan removal tool for Snow Leopard. This seemed to work for about 10 minutes, but the apps and videos quickly started lagging and slowing down my whole computer again. If anyone else has experienced anything like this, I would love to hear exactly what has happened to you and to see what you did to [try to] fix it. Thanks for reading all of this, I need all the help I can get right now. Also, I can't watch The Daily Show or The Colbert Report on Hulu anymore, and it's killing me! Thanks again.

Answer 1

It's very difficult to say without knowing more about your system. There are a number of possibilities. First, your 13" lacks a discrete GPU, so the CPU is doing the work that a GPU would have done as far as decoding video streams, etc. Each video stream will consume considerable resources from the machine, and if you have multiple things running with video streams being decoded (for example, a browser with video Flash or cumbersome animation and iMovie running at the same time), then that may be a factor.
Additionally, it could be that you are memory constrained. You didn't post a picture of the process list from activity monitor or the memory usage stats, but you probably want to look and see what the memory and CPU usage is and who's consuming what. Some applications are pretty inefficient. For example, if you have iPhoto open and have thousands of images, the indexed metadata and thumbnails are all stored in RAM. iMovie pulls in clip thumbnail sets - (and worse, it has to do on-the-fly transcoding video assets from some cameras that don't encode the video using the parameters it expects to make indexing frames easier). Again, this would show up as periodic spikes in CPU activity for the app.
You seem to have plenty of disk space, that's not likely to be a problem.
Check if Time Machine is running. Time Machine introduces a performance impact, but it's exacerbated by the presence of frequently changed large files (e.g., you don't want Time Machine backing up your video projects while you are working on them).
Lastly, you may consider checking the console for error messages. This might reveal background processes that might be bogging down the system, or things like filesystem/disk errors. If there are errors in the filesystem, when you access certain portions of the disk, the OS and applications can slow down or lock-up as a result.