A good question, unfortunately no good answer 🙁
The question: How can I playback more than one recorded streams in synchronization?
This is definitely something that has been requested a billion times to the FMS team. Hopefully they are working hard on getting this going. To put it in a short sentence, “you can’t”. It sucks..
But what you can do is try to start playing them both at the same time with a low buffer. Like .5 of a second or something. Then when they are playing, up the buffer a bit to keep things in line. While the videos are playing, you also can keep a watch on the time that the videos are at and if the difference get’s too high, just pause one and let the other catch up.
This requires quite a bit of coding and calculation because you have to figure out how much is buffered, how long it took to buffer, the difference in times of the videos, if the videos are staggered that will add even more trouble.
It’s not that it can’t be done, progressively it would be reasonably easy, just preload lots 🙂 Streaming is a bit hard as you have to always buffer. On the flip side, using seek() to get to a point in the stream is good because you don’t need to preload that part of the video to start playing it.
So, in conclusion, it can be done I guess, but it’s your best calculations that are going to run it. This kind of feature is not built into FMS.