The support for this is questionable. It's barely acceptable in Chrome and even in Chrome it falls really short.

The timing is awful in a lot of cases which makes it pretty much unusable for anything but maybe background tracks. I've had audio clips that had to be played in a 50ms time frame fail to play back a third of the time on occasion.

I'd rather have no sound than buggy sound.

Thanks for your link, but I've investigated MIDI support in JS. I actually work on piano/guitar apps, and would love to build a high performing, low latency app that hooks up with a physical keyboard. If you know how this can be done, please let me know! The last time I looked into this, the best solution I could come up with was a Java applet. :-(

The way forward is going to be via the Google-led Web Audio spec, as well as the complementary MIDI device spec - it's not "there" yet, though, since these specs are still non-finalized. But I'm working on building up the playback capabilities as a side project. I made a "true" Soundfont2 + SMF playback engine for Flash/Haxe, which is open-source(zlib) and somewhat usable in real-world: http://spacecreeps.com/apps/triad-synth/index.html

Now I'm working on the next generation of it, since I was still learning my way around audio with that one and made a mess of the architecture. I'm starting off with a Web Audio-for-Haxe project( early stages, you can watch it here https://github.com/triplefox/hxAudio ) - I'll be building off of that to add the synthesis and MIDI parts, so that you have pretty much everything needed for the playback parts of an audio app; recording isn't on my radar yet - especially since the specs are very early still. It will be possible to compile out the lib to pure JS, so you won't necessarily have to be using Haxe if that's not your workflow.

Aaand one of those demos killed Safari