Comment 5 for bug 956934

It's trying to generate thumbnails for movies without Nautilus generated thumbnails (and caches them in ~/.cache/unity-lens-video when it's done so it doesn't have to generate them several times). But the lens doesn't allow more than three thumbnailers running at the same time, so some disk IO the first time the video lens encounters a file without thumbnail is normal, but what happens to you is a bit extreme.

Could you please test the following changes?

In a terminal:
gksu gedit /usr/lib/unity-lens-video/unity-lens-video
And on line 91 of this file:
replace "Q_MAX = 3" by "Q_MAX = 0".
It will prevent the thumbnailer to start, Q_MAX being the size of the thumbnailer queue.
Then delete the ~/.cache/unity-lens-video folder and log out.

The lens shouldn't try to generate thumbnails anymore and only shows thumbnails for videos having Nautilus generated thumbnails. If the intensive disk IO is gone, it means we need to be smarter about how the thumbnailers are handled and probably avoid the thumbnailing on some videos.

If the intensive IO is still here, it means it's another bug.