Download an open-source audio sequencing program to your computer (see Resources). These are typically free, easy to use and perfectly adequate for the purposes of recording audio from a television set.
Plug a microphone into your computer sound card or audio interface. Open the audio sequencing program and sound-check the mike. Speak into it and monitor the output meter. If it goes red, turn the gain down on the sound card or audio interface.
Insert the DVD, press "Play" and turn the volume loud, but not so loud that it is fuzzy. Forward the DVD to about 20 seconds before the sound appears in the soundtrack. Point the microphone at the speakers on the television and press “Record.” You’ll capture a lot of superfluous audio, but you are guaranteed to capture the entire segment that you want. Once you’ve captured the sound, press “Stop” on the program. Then press “Save.” If you don’t have the DVD and are recording from a television broadcast, make sure that you are set up before the movie begins.
Open the editing tool box on your audio sequencer software. Enlarge the audio track that you recorded onto so that you can see the waveform of the sound. Play the sound five or six times and view the waveform. Locate the points on the waveform that represent the start and end of the sound sample. Select the “scissors” or “trim” tool. Cut the waveform so that only the desired sound sample remains. Delete the extra audio. Press “Save.”
Alter the sound. Using a copyrighted sound effect in commercial work requires clearance from the copyright owner. If you plan on using the sound in your own, non-commercial creative work, it’s smart to alter it so that it isn’t instantly recognizable as a movie sound effect. Add reverb, compression or distortion to alter the characteristics of the sound file.