macOS High Sierra unable to natively play videos encoded with HandBrake's H.265 setting

I'm using HandBrake to encode some videos using the MP4 H.265 format, but the videos won't play using QuickTime or Quick Look on macOS High Sierra, which is supposed to have H.265/HEVC support. They work in VLC just fine. Anyone else have this problem or know why these videos won't play in the system-provided players?