Try removing \ before video. I think it is not needed if you use tooltip:
If(isEqual([Dolby Vision],1,8),<img src="tooltip:Video\dolby-vision" height="25">,)
Using isEqual is perfectly fine but if you like and as [Dolby Vision] is empty vs 1 field you can also just check against raw value [Dolby Vision,0] meaning if there is a value in [Dolby Vision] then If return true i.e 1
If([Dolby Vision,0],<img src="tooltip:Video\dolby-vision" height="25">,)
or user isEmpty negative check
If(IsEmpty([Dolby Vision]),,<img src="tooltip:Video\dolby-vision" height="25">)