Yes, you can use Haali Video Renderer, but it has one bug, if the video resolution is close to or equal to the screen resolution, then for some reason the video opens reduced.
No, codecs still optimize, for example on Core 2 Duo E6700 Conroe, 2.66 GHz, you can watch FHD h264, h265 and VP9, only for FHD AV1 lacks performance and it slows down, but 720p goes smoothly.