Force videos to play at 30 fps

[rfc-2549]

I use a thinkpad T400 which has a core2duo processor. Meaning it can't play 1080p 60fps videos without exploding. I'd like to force mpv to play videos at 30fps.

I have the mpv config like this:
arg => "--really-quiet --title=*TITLE* -ytdl-format=\"bestvideo[height<=?1080][fps<=?30]+bestaudio/best\""

Meaning that it will download the video at 30fps and 1080p but that does not seems to work. It still downloads the video at 60fps and overheats the processor.

Thanks