The effective Stock Footage skill set includes (at least):
1. Subliminally registering important words,
2. Following the tone and cadence of your partner's voice while ignoring its content,
3. Judiciously interjecting soothing phrases when appropriate,
4. And, (the most expert skill) responding to the dreaded "Are you even listening to me?" or somesuch query by reconstructing from one's subconscious mind enough of the meaning of the fellow communicant's narrative to prevent a highly undesirable incidence of Color Bars.
Speaker A: "...and so she says to me 'no way' and i go 'you've GOT to be kidding me' and he goes 'no you DIDN'T' and then they both started in again with the, you know, and I was like so... "
Speaker B: "So.. what?"
Speaker A: "Embarrassed, you know? Are you even listening to me?"
Speaker B; "Yes, of course, they were at it again with the same old same old can you believe it?'
Speaker A; "I know! And then she was like..."
Stock footage can also be used to integrate news footage or notable figures into a film. For instance, the Academy Award-winning film Forrest Gump used stock footage extensively, to portray the lead character meeting historic figures such as John F. Kennedy, Richard Nixon, and John Lennon.
One of the largest producers of public domain stock footage is the United States government. All videos produced by the United States military, NASA, and other agencies are available for use as stock footage. There are a number of companies that own the copyrights to large libraries of stock footage and charge film makers a fee for using it, but they rarely demand royalties. Stock footage comes from a myriad of sources, including governments, other movies, and often news outlets.
Television and movies series also often use stock footage taken from previous installments. For instance, all the Star Trek series kept a collection of shots of starships that would appear on a regular basis, being used most of the time a ship was seen.
News programs use film footage from their archives often when more recent images are not available.
My credits: wikipedia