Choppy resulting video

Hi:
This is one of the best tools that I've found!, the only issue is that the resulting video when trying to transcode an AVI, MKV and so on with spanish hardcoded subtitles will be choppy. My system specs are not that bad ;)
Tried to check starting the app from a terminal and no errors were displayed so I'm clueless. From a command line mencoder adding subs will work just fine. I just like the preview feature. If you guys have had seen this issue before and know how to fix it will be greatly appreciated.
If someone is interested in checking the resulting video it can be found here www dot linuxreign dot org /arista

Reproduce the choppy output by using the Arista app to transcode an AVI or MKV with Spanish hardcoded subtitles, then compare it with the command-line mencoder result. Check the app's terminal output and preview behavior; done means the resulting video plays smoothly while subtitles remain present.

Written by the indexing model from the issue text.