Hello,
I can crash V2.6.7 r8999 when doing the following steps:
1. Open any video file to convert
2. Choose any video/audio settings
3. Choose "Save Video"
4. Stop the conversion process by clicking on the upper right X of the progress window (don't use the Pause/Abort button)
5. Choose "Save Video" and select the same output file again
6. Avidemux is unable to open that file (I guess it's still locked), displays several error messages and crashes after confirming all of them