Using samples from http://www.dvc.uk.com/acatalog/GH4-Sample-footage.html - I able to read plant.mp4, tree.mp4, beach_uhd.mp4 - but it seems the hosted samples' durations are shorter than reported on file's properties.
Tree.MP4 for example, specified 17 secs, but when played back with Win Media player, it's just 6 secs? - put into VP14's timeline, after 00:05:18 - it's just blank.