Watch sources explained

A "source" is one upload of the film on YouTube. Films often exist on more than one channel — an official studio channel and a regional distributor, for example — so a movie page can offer more than one Watch button.

• Our crawler re-checks sources regularly; ones that disappear from YouTube are deactivated automatically.
• New uploads on trusted channels are picked up daily (and within the hour for channels we watch closely).
• Viewer reports also flag dead links between crawls — see "Report a broken link".