Whenever I play HD movies on my computer (720 and up), after about 15 minutes or so it starts lagging horribly and I realize (via Samurize) that I have < 1% RAM free. However, when I open up the task manager no app, including the media player I'm using (I've tried VLC and MPC), is using anywhere near that amount.
This could be bad Video Drivers, make sure you are at latest.
Also, Task manager is not always reliable. Download Process Explorer and run as an administrator / elevate with UAC.
Run a HD Movie and then either look at what is taking up your RAM or click on one of the historical graphs at the top of the screen and hove over the peaks in RAM and it should tell you what is taking up the most at that moment.
Process Explorer is a VERY good tool for anything like this.
edit - Thanks Alan Haggai Alavi, I posted wrong link! Multi tasking is not my friend!
Something similar(laptop would turn off due to heat) would happen to me as well. I found that using your GPU's hardware acceleration helps alot and takes a big burden off the CPU. You can use CoreAVC codec but it is shareware or try this link
Look at Post #17
If no application is using the RAM then it is going to the operating system somewhere. That would be file cache or a driver.
A video driver would be a likely culprit. Simply being on the latest version does not guarantee anything, because every bug was new some time. It could even be a combination with your hardware: the Radeon 4850 is fairly old at this point and AMD may not be testing the drivers carefully with that hardware.
File cache should show up in Task Manager. It's possible that the video playback is causing the file to be read into memory in preparation for playing the video.
It's possible that RAM use has nothing to do with your problem. Every Vista system I've seen reports RAM use to be very high. This is because Vista uses as much RAM as it can for program, DLL and file caching. It isn't normally a problem because this cached memory is easily discarded to make room when needed.
