I had to remove this feature to get it to work on safari. Apple hates autoplay sound. (which as a user is overall a good thing)
As long as you do it as part of a user gesture it should work. Make sure the actual play() is called from within the context of a touch/mouse event, that should be enough.
Thanks.
It would still be nice if users can enable sound for all videos with one click. Currently you have to enable sound on each individual video.