First find the clips from whatever show or movie you are pulling from on YouTube.Copy and paste the URLs from the videos into keepvid.com. You can choose what to convert the video into on the site. Choose an audio file such as an MP3.
Finally, open the MP3s in audacity and edit them down to just what you need.You can delete portions by highlighting and pressing delete. Patch the final edits together, and you’ve got a mash-up!