How to start a method in the same time on 2 devices

Question

I have 2 android phones phones, both connected to the same wifi, both with bluetooth.

I want some method that syncs somehow the phones and starts a function on the same time on both phones.

For example playing a song at the same time.

I already tried with bluetooth but its with lag, sometimes 0.5 secs. I want something in +- 0.01sec if possible.

Someone suggesting playing it in the future with 2-3 seconds, sending the time-stamp, but how do you sync the internal clocks of the devices then ?

Answer 1

Before calling that particular method, try to measure the latency between the two devices:

1.First device says Hi(store the current time)

2.Second device receives the Hi.

3.Second device says back Hi !!

4.First device receives the Hi.((storedTime - currentTime) / 2 )

Now you have the latency, send your request to second device to start your particular method and start it on first one after the latency.

Try to measure the latency 5 to 10 times to be more accurate.

Answer 2

you have a way to transfer data between the devices right ? if so you can send a time-stamp which is in the future, ex: if the present time stamp is 1421242326 you send 1421242329 or something and start the function at that time on both devices.