Trimmed Video Trims Sound OK, but Not Video

mike s.

Young grasshopper
Dec 12, 2014
40
4
I'm trying to trim and export a BI video into MP4. I set the start and stop points, and exported. But when I play back the MP4, the sound is there but the video is just a still shot from the beginning of the video. Any idea what's going on?
The system is dual-core 3 ghz, 4 gb RAM, and is not used for anything other than running BI.