So you have that video of your cat doing that thing and that other video of your brother getting startled by the can of joke peanuts, and now you’re thinking “I’m such a wicked director I’m going to edit these films together and put them on the Interwebz”. Ok. That sounds important.
In Ubuntu there is a little utility called avimerge which (wait for it) merges avi files.
avimerge -c -o [WhatYouWantItCalled].avi -i [a].avi [b].avi
I know; you’re thinking “dude, that looks like something you type into the terminal window; how am I supposed to do this?”. Fear not, little tomato. You just want to replace the stuff in the square brackets with your stuff. A and B are the two files you are wanting to merge and WhatYouWantItCalled is, well, I think you can manage that one. Yours might look like this:
avimerge -c -o ScorseseMe.avi -i CuteKitty.avi BroJumps.avi
If your file names have spaces you’ll have to tell the shell (the terminal) how to interpret them:
avimerge -c -o “Scorsese Me.avi” -i “Cute Kitty.avi” “Bro Jumps.avi”
avimerge -c -o Scorsese\ Me.avi -i Cute\ Kitty.avi Bro\ Jumps.avi
(The quotes tell the shell to interpret what comes between them as a single item or word; normally words are space-delimited and here the quotes prevent the command from interpreting the space as the end of the file name. The slash is what is known as an escape character; the character which follows the escape character is escaped and thus not interpreted by the shell but read just as another character.)
Could it be any easier?
Have fun with that.