Both VA-API and VDPAU do not play video on GK208B using mpv. There was only
sound and black screen.

Linux 5.2.7-arch1-1-ARCH
local/libva-mesa-driver 19.1.4-1
local/mesa 19.1.4-1
local/mesa-demos 8.4.0-1
local/mesa-vdpau 19.1.4-1

$ LIBVA_DRIVER_NAME=nouveau mpv --hwdec=vaapi -vo=vaapi /path/to/MP4
Playing: /path/to/MP4
 (+) Video --vid=1 (*) (h264 1280x720 23.976fps)
 (+) Audio --aid=1 --alang=eng (*) (aac 2ch 44100Hz)
Using hardware decoding (vaapi).
AO: [pulse] 44100Hz stereo 2ch float
VO: [vaapi] 1280x720 vaapi[nv12]
nve4_set_surface_info:969 - unsupported surface format, try
is_format_supported() !
nve4_set_surface_info:969 - unsupported surface format, try
is_format_supported() !
nve4_set_surface_info:969 - unsupported surface format, try
is_format_supported() !
nve4_set_surface_info:969 - unsupported surface format, try
is_format_supported() !
nve4_set_surface_info:969 - unsupported surface format, try
is_format_supported() !

$ VDPAU_DRIVER=nouveau mpv --hwdec=vdpau -vo=opengl /path/to/MP4 
Driver 'opengl' has been replaced with 'gpu'!
Playing: /path/to/MP4
 (+) Video --vid=1 (*) (h264 1280x720 23.976fps)
 (+) Audio --aid=1 --alang=eng (*) (aac 2ch 44100Hz)
Cannot load libcuda.so.1
Using hardware decoding (vdpau).
VO: [gpu] 1280x720 vdpau[yuv420p]
AO: [pulse] 44100Hz stereo 2ch float
AV: 00:00:12 / 00:02:03 (10%) A-V:  0.000