A quick way of searching for copyright cleared images online is using Creative Common licenses.
Videos can be used for teaching or instruction purposes. To do this the audience needs to be staff and students.
In addition the film shown needs to be about the topic you are teaching.
For online video clips it is best to contact the clips copyright owner. As material can be placed illegally online. This is good advice for sites that host large numbers of videos like YouTube.
Requesting off air recordings 
The LRCs currently offer an off air recording service for television broadcasts. This uses the ERA license scheme. Below is more about what is involved.
The recordings are for non-commercial educational purposes. Channels cover include:
To find out more or request a recording contact your subject librarian
Don't forget to check all copyright holders are covered by any exception or permissions you get. It is likely a number of people were involved in created music and videos.