Inserting video captured from VLC

I'm having trouble inserting video. I'm capturing live streams using VLC and saving them as MP4. Once inserted into Storyline, they behave unexpectedly:

1) using VLC's record function I can save a clip into a specified folder in MP4 format. Inserting these clips makes Storyline unresponsive. Instead of the usual progress bar, the video is inserted seemingly immediately - it appears on the timeline and the ribbon changes to video options - with the slide turning black after a few seconds, but I can't click anything within Storyline. I have to use Task Manager to crash out (although the application is still showing as running).

2) Using VLC's convert/stream option I save a clip as MP4. These insert just fine, but appear to have no audio. Once I publish, the audio is there, however.

I've inserted many different "flavours" of mp4 without problems before so it appears to be something about the VLC capture that is causing the problem. I know very little about codecs and the like...

Has anyone had any luck inserting videos saved directly from VLC???