Sample url: https://www.pbslearningmedia.org/resource/mkcpt-math-g-areatri/area-of-a-triangle/
PBS Learningmedia is an edu streaming site that features tons of
videos for you viewing pleasure.
The site has an Alexa rank of 32601, which is considered to be quite good.
To download PBS Learningmedia videos you can't use the dl-trick but you can always just copy-paste it or use our bookmarklet shown in the top menu.
More info about PBS Learningmedia is coming soon.