Found a crash? Generate us a backtrace:
1) Run “gdb mixxx”
2) When the gdb prompt appears, type “run”.
3) When Mixxx crashes, type the following into the gdb prompt: “thread apply all bt”
4) Submit the bug using the Mixxx bug reporting system on Launchpad. Bugs filed here are trackable by developers and will not fall through the cracks as easily as using the IRC channel or mixxx-devel. Make sure that the bug you are filing is new, and if you think that another bug might be the same one, post comments on it with your backtrace and any other useful info.
5) If you do not want to use Launchpad, post the results in the forum, email them to mixxx-devel, or pastebin them and drop the link on IRC. We'll then try to figure out where the crash is. Do not assume a developer will hear you in IRC, using a static system (bug tracker, e-mail, forum) is much preferred. The IRC channel is great for technical support though.
Note: To get a backtrace for a thread freeze you can do the same thing as above, but to get the gdb prompt, you have to press CTRL+Z in the terminal window to suspend Mixxx.