Fix hwaccel for AMD APUs #4701

[Jglrz]

This fixes ffmpeg hardware acceleration for AMD APUs #4701

[NodudeWasTaken]

This is inappropriate given that -2 is used to scale a video with respect to its aspect ratio, this is both used in the test and in practice when scaling. Please try increasing the test resolution instead, that might do it.

[WithoutPants]

Closing in favour of #4765