The idea of a media master class is to teach a subject using technology in the music classroom. It can be used by using videos or recordings that can be found online. For instance there is a website called yourepeat.com that uses youtube links and lets you repeat any section of the video over and over again. All you have to do is replace the "tube" in "youtube" and replace it with "repeat" in the url and you will instantly get to the yourepeat.com link. This can help a musical group learn a specific part of the song they are trying to learn by isolating that specific part. It can also be used for jazz ensembles trying to learn how to improvise by repeating a 12 bar blues over and over to have everyone in the band take a turn improvising.
This video is an example of demonstrating the style of playing that a director might wish out of his jazz ensemble.
Spotify is also a great resource that can be used for free or with the subscription fee. It contains many good recording of contemporary as well as jazz, wind ensemble, and choral music that can be a great resource for a music educator. For example, Dr. Wiley my jazz ensemble director showed us that most of the recording of the songs we were playing in a past concert were available on Spotify. We even listened to two songs during rehearsal and helped us understand the sound he wanted us to produce.
In conclusion, there are many resources available for use online that can help music teachers in the classroom convey what they want from their students in a fun way.