If you don't generate this caps information, you will also get errors while
encoding that look like this:
(gst-launch-0.10:1580): GStreamer-CRITICAL **: gst_caps_unref: assertion `caps
= NULL' failed
The fact that source caps information was never generated for MPEG-2 looks
an oversight -- the static caps for TIVidenc1 already allowed MPEG-2.