What's the best way to calculate remaining download time?

Question

Let\'s say you want to calculate the remaining download time, and you have all the information needed, that is: File size, dl\'ed size, size left, time elapsed, momentary dl

Answer 1

Well, as you said, using the absolutely current download speed isn't a great method, because it tends to fluctuate. However, something like an overall average isn't a great idea either, because there may be large fluctuations there as well.

Consider if I start downloading a file at the same time as 9 others. I'm only getting 10% of my normal speed, but halfway through the file, the other 9 finish. Now I'm downloading at 10x the speed I started at. My original 10% speed shouldn't be a factor in the "how much time is left?" calculation any more.

Personally, I'd probably take an average over the last 30 seconds or so, and use that. That should do calculations based on recent speed, without fluctuating wildly. 30 seconds may not be the right amount, it would take some experimentation to figure out a good amount.

Another option would be to set a sort of "fluctuation threshold", where you don't do any recalculation until the speed changes by more than that threshold. For example (random number, again, would require experimentation), you could set the threshold at 10%. Then, if you're downloading at 100kb/s, you don't recalculate the remaining time until the download speed changes to either below 90kb/s or 110kb/s. If one of those changes happens, the time is recalculated and a new threshold is set.