Uninstalled CRT 2.0, and installed the drivers from Asus. DXVA checker now reports:
ASUS EAH6450 (Caicos Pro Refresh)
MPEG2_VLD: DXVA2, SD / HD / FHD
MPEG2_IDCT: DXVA2, SD / HD / FHD
MPEG2_A: DXVA1, SD / HD / FHD
MPEG2_C: DXVA1, SD / HD / FHD
H264_VLD_NoFGT: DXVA2, SD / HD / FHD
H264_VLD_NoFGT_Flash: DXVA2, SD / HD / FHD
6719B6FB-5CAD-4ACB-B00A-F3BFDEC38727: DXVA2
VC1_VLD: DXVA2, SD / HD / FHD
CA15D19A-2B48-43D6-979E-7A6E9C802FF8: DXVA2
MPEG4pt2_VLD_AdvSimple_Avivo: DXVA2, SD / HD / FHD
MPEG4pt2_VLD_AdvSimple_NoGMC: DXVA2, SD / HD / FHD
Note the last 2 lines. They are new. All MP4 videos play fine.
Also, I know why "generic video adapter" works as well. According to DXVA Checker and DXDIAG, there is no hardware acceleration available. All empty. All software.

Does all this help??