Since there is no information about the source format, "unspecified"
is the correct value to write here.
All tests using the MPEG-2 encoder are updated, as this changes the
header on all outputs.
The new reference.pnm is a freely licensed replacement. The photo has
been taken by Reinhard Tartler on August 28 2014, and is licensed under
the expat license as stated at http://www.jclark.com/xml/copying.txt
