Our services of Shared Motion provides timing accuracy of a few milliseconds (thousandths of a second), and works on all mayor web browsers.  

We have worked hard to make the service as simple to use as possible for programmers - just add a couple of lines of JavaScript to your web page and the timing objects become available.   We also provide some libraries you can use to synchronize audio and video files, get your timed data played back and so on.  These are provided "as-is" and for no charge.