There are a few things that can cause stalling (basically this means that MixEmergency isn't able to read the frames that it needs - and it should continue, but will do so very slowly). One of these problems has been fixed in MixEmergency 1.6, and will only occur under certain conditions with your videos. Can you send me an e-mail about this, and I'll see if we can do some further tests to figure out if this is a separate problem. As to decreasing the number of passes, I would recommend using one of our single-pass presets (i.e. the "Fast" presets). If you're using a custom export preset, then make sure that "multi-pass" is disabled.
