Comment # 5 on bug 99029 from Alex Deucher

I'm not too familiar with VAAPI, but for transcoding, you really need efficient
pipelining between the decode and the encode.  If there are CPU copies in the
middle, performance won't be great.  We generally recommend using gstreamer
with OpenMax using tunneling so that there are no extra copies between the
decode and encode stages of the transcode.  I'm not sure if VAAPI supports
something like this.