Audio files should be preloaded before use for better sync before playback.

[robertbryer]

If playing back on a connection that isn't particularly fast, there will be a delay before the audio sources start playing back. We should make a cue for a certain number of seconds before hand to set .preload = true on the media so that it is ready to go when it hits play.

We should also at this point investigate if we can use https://www.w3.org/TR/media-frags/

#t=10,20

To truncate how much gets downloaded when preloading - the behaviour likely depends upon the browser, but worth looking at.