mpeg2enc: make it a gstvideoencoder subclass

Submitted by Alban Browaeys

Link to original bug (#685414)

Description

Created attachment 225695
mpeg2enc: initial switch to gstvideoencoder base class

the aim was to make mpeg2enc succeed to encode in pitivi . It does via:
gst-launch-1.0 videotestsrc num-buffers=10 ! mpeg2enc ! filesink location=videotestsrc.m1v
ie buffer could be increased/decrease, mpeg2enc format= works there.
but pitivi still fails in various area, audioteee not-linked or else. So not tested in real world scenario as I do not have one working.
At least pitivi is not segfaulting in mpeg2enc anymore but this might comes from a lot of things. After a long time pitivi start to render but timeout increase with time spent and the file is always 20k.

Patch 225695, "mpeg2enc: initial switch to gstvideoencoder base class":
0001-mpeg2enc-initial-port-to-videoencoder.txt