Here are test results made on Intel Core2 Duo E8400 @ 3.00GHz.
The video length is 02:05:02 with resolution 720x428@25fps

pipe line:
time gst-launch-1.0 filesrc location=in_den_schuen_meiner_schwester.mkv ! matroskademux ! vp8dec threads=2 ! fakesink

with threads=1:
real	15m7.971s
user	14m18.613s
sys	0m9.595s

with threads=2:
real	11m59.063s
user	13m10.811s
sys	1m11.575s

Created attachment 211827 [details] [review]
patch v2

new patch, changes:
- rename options threads to max-threads. It describe better what it actually do.
- set default count of threads to 8. This is limit used by decoder. Decoder will decide haw many threads to create. It checks number of cores and number of token parts. We can't do better decision than decoder. If, for some reason, user need to limit number of threads, he can use this option.

This is fixed in 0.11 now, while reworking all the decoder and encoder properties.