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Audience Retention has been a much guarded secret at YouTube. I posted about it's importance on 11 May 2014 (don't go there now, wait till you've read this post, thanks - it will make more sense for you).
For any video, the public can see a View Count and usually a Statistics area that outlines Time Watched, Subs Driven and Shares as Cumulative/Daily.
The key to finding Audience Retention is More | Statistics | Time Watched | Average View Duration and then some maths.