Latency with Multipeer Connectivity framework

Question

So I've been dumped with a very broken and outdated code base. I'm being asked however to fix only one bug with the latency that occurs when a message is sent between two devices.

The app is for streaming audio to several devices and playing them all at once. The issue is obviously caused when the host sends a "play" message and starts playing itself. This play message is delayed by up to 3 seconds and therefore the clients all end up out of sync.

I've attempted sending a CFAbsoluteTimeGetCurrent(); value to the clients where they then work out the latency but device clocks are very unreliable and I often get negative differences in time despite obviously being positive.

Any idea on how I can combat this? And before suggestions of changing the method entirely, there's isn't much time

Answer 1

Have you considered sending a SYN message along with a local timestamp and then have the per return the timestamp as a ACK message? You can take the difference between the current time and the return time and half it to get a latency.

Source: I did this.