ff-h264 yuv420p

I’m using AFTV2 with Kodi Krypton, when playing videos from Youtube, I see a lot of videos can’t be played with hardware decoder, they are all played with “ff-h264 yuv420p” software decoder, thus there is lag when playing 1080P/720P videos. Is this normal? I can’t imagine Amazon doesn’t support this type of encoding with hardware, because it’s so popular in Youtube videos. Any one have any idea on this?