Mime type not identified for matroska / mkv files

Steps to reproduce:
1. Add a workflow which includes mkv / matroska as intermediate format
2. Inspect mediapackage
3.

Actual Results:

mkv files have mime type "undefined"

MediaInspector logs error, e.g.

2014-12-03 16:14:04 ERROR (MediaInspector:155) - Unable to find mimetype for /data/matterhorn/work/shared/workspace/collection/composer/40298477.mkv

Expected Results:

mimetype should be "video/x-matroska"

Workaround (if any):