HD Graphics 620: VAAPI performs poorly

"Recently" I've stumbled over the temperature issues described in #953 (closed) (which is likely a duplicate of #614 (closed)) and made in addition the observation that (even under kernel 5.2, where, AFAIU, the issue of #614 (closed) shouldn't be present) playing back videos with VAAPI result sometimes in higher temperatures than playback without hardware acceleration.

@ickle suggested to file a separate bug for this.

And in general, it seems to perform pretty poor, playing back e.g. a 1920x1080 H264 video in fullscreen on a HiDPI display, causes the CPU/GPU reach 100°C ... but maybe the HD620 isn't just powerful enough... still it shouldn't perform worse than pure software acceleration, as it does in some cases at least.

For details of my testing methods, versions, etc. please have a look at #953 (comment 380857) .

Maybe someone could have a look :-)

Thanks, Chris.