[fritsch]

Reading as much of this thread as I can digest it seems that if you have a system with Intel Graphics older than Haswell then you can forget achieving anything near decent deinterlacing quality for video sources (in particular broadcast TV) as you're limited to Bob and on top of that if the source is MPEG2 the results of this are even worse than you would normally expect due to bugs in the drivers?

If the CPU is fast enough, you can use Yadif deinterlacing (Deinterlace) on the CPU while still decoding on the GPU with VAAPI. Only the "gpu internal" deinterlacers won't work, cause of non working implementation on the intel driver side. Here HSW or newer is needed.