If your Mac freezes, becomes unresponsive, or is generally slow and stuttering while watching a 1080p of high definition movie in VLC, there is a solution. I have a quad core Mac with 8Gb of memory, so playing high definition movies shouldn’t be a problem. However, after a while, usually an hour into a movie playing off my hard drive (for example a .mkv or matroska file) it will freeze for a couple of seconds, while the sound is playing, or become blocky, at the end of the file it would take a couple of minutes before my Mac would become responsive again after quitting VLC. This is a problem, thankfully it has a simple solution.
Open up VLC and access the system preferences from VLC > Preferences. Select the option of All at the bottom of the screen. Within the settings go to:
Input / Codecs > Access Modules > MMap > Disable “Use file memory mapping”
This will stop your VLC movie freezing problem. Note that in VLC 2.0, this problem has already been fixed and disabled.
This should enable VLC to play your HD movie perfectly fine with no interruptions.
By the looks of the settings it disables something called MMap, after having a quick read around it seems to be a method of moving the file into memory and reading the file from memory instead of from disk. However, it also seems to be a problem for VLC and your Mac and numerous problems seems to be associated with it.
It is only a simple solution, however one that has allowed VLC to work perfectly from now on. If you have some problems with VLC this is probably your solution.