Calculate unique viewership duration

I thought you wanted to make sure overlapping views were included not excluded.  Here is a different measure that will calculate the overall duration watched for each customer and video combination.  Note this works with your example data, but if you have a customer that watched the first 10 sec and last 10 sec of a video, it would calculate the whole video duration.  A more complex expression would be needed to avoid that.  I didn't have time to do that now, but may later.  Perhaps the below approach will be enough, or get you started.

NewMeasure =
SUMX (
SUMMARIZE ( Table, Table[Customer ID], Table[Video Name] ),
CALCULATE ( MAX ( Table[Stop Index] ) - MIN ( Table[Start Index] ) )
)

If this works for you, please mark it as the solution.  Kudos are appreciated too.  Please let me know if not.

Regards,

Pat