If you think you've found a bug in the software, first make sure you're using the latest version from www.mixxx.org, then check the FAQ, the Troubleshooting page and the forums to see if there is a known solution or workaround or if other people are having the same problem.
If you don't find anything there, our bug tracking system is located at https://bugs.launchpad.net/mixxx. First try a few searches on various keywords related to the problem to see if it's already been reported and what the current status is. If you find one or more that relate, click change on “This bug doesn't affect me” to “vote” for the bug (you may need to sign in to see this.)
If no existing bugs cover your issue, please gather the following information:
Much of the system information can be gathered from System Information in Windows (found under Control Panel→Administrative Tools→Computer Management→System Information,) and with the commands uname -a and lspci -v on Linux.
Copy the following information and paste it into your bug report (or add it as an attachment)
gdb --eval-command=run mixxx
Reproduce the crash mixxx and then type thread apply all bt at the (gdb) prompt and copy the lines from your terminal and paste them into the bug report.