"refreshDuration" corresponds to the frequency in seconds of the hits sent to our servers to inform that the media is playing content. For example, if you select 5 seconds, a hit will be sent every 5 seconds while the content is playing. The more the frequency is reduced, the more precise will be the duration of the playing time.
When tagging your website, you can choose to set only one duration that will be the same during the entire playing of your media content (for example, every 5 seconds for a 5 minutes content) or you can as well set an evolutive refresh regarding the total duration of the content (for example, from 0 to 1 minute a frequency about 5 seconds, then from 1 minute to 3 minutes a frequency of 10 seconds and finally, from 3 minutes to 5 minutes, with a frequency of 15 seconds).
Don't forget to have a look at Rich Media and evolving refresh duration in our tagging guides.