We can’t be sure that the delays are due to buffering, since unfortunately the result lines do not give us that information. It could be that no participant ever experienced buffering issues, but only slowdowns due to their browser’s poor performance at the time they took the experiment.
For the same reason, using the end time will not give you more accurate measures, because you don’t know what exactly caused the delay.
I realize this is a really frustrating situation, and I apologize for it—you expect the experimental software that you use to give you accurate measures, and PennController clearly failed to do so in this case. I will do my best to improve PennController’s performance.
Then again, many other factors can impact the quality of one participant’s data, including the browser they use and how they use that browser. Safari for example is known to handle media elements differently from Chrome or Firefox (which I use to develop PennController). If you see that only some participants’ data manifest this kind of delays, it could be indicative that their specific configuration (eg. using a specific browser) contributed to the delays, and hopefully you could decide whether to filter them out for analysis purposes.
Jeremy