itsquiethere
See the 15th post from -> https://forum.dvdfab.cn/d/404024-streamfab-faq/15
Keep in mind when you download from Apple TV, if you select Dolby Vision, the file it downloads is Dolby Vision only, no fall back to other methods like HDR10.
So as Sebastian001 says, if you selected Dolby Vision when you downloaded, and something in your playback chain doesn’t support Dolby Vision, which is why you’re getting the purple colors
