The file tracker, the daemon which identifies and categorises files, is not run always. There may be some logic to run it only at nights or when connected to PSU for charging. I noticed one night, when suddenly CPU usage was all the time 100% and at 600 MHz for quite some time, that "tracker" was the culprit. But after it has done it job, the device was idle again. Shame you didn't get it working. Ogg, Vorbis and Theora would be the "politically" correct targets to transcode media-files to.