Currently the only measure of usage of videos and audio files is the number of page views of pages on which appear, measured using tools like stats.grok.se. Because videos and audio files must be clicked on to play, using page views is a very inaccurate measure.
A publicly available view counter of number of times videos and audio files have been played across all Wikimedia projects would offer a much more accurate understanding.
This is metric is especially important for people (like me) working with partner organisations considering making content available under an open license. I'm not currently able to offer these organisations any sort of useful information about how many times their content has been seen, where as commercial sites e.g Youtube that do not require an open license can offer information on the number of video views.