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Re: Web Audio API is now available in Chrome

From: Chris Rogers <crogers@google.com>
Date: Tue, 1 Feb 2011 15:05:13 -0800
Message-ID: <AANLkTimm+RD652RxP_wN3PM6sC=OGaVwEYoqMph1aWVo@mail.gmail.com>
To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Cc: "Tom White (MMA)" <lists@midi.org>, public-xg-audio@w3.org
Hi Silvia, thanks for your comments.  I have a few responses below:

On Tue, Feb 1, 2011 at 1:43 PM, Silvia Pfeiffer

> On Wed, Feb 2, 2011 at 6:54 AM, Chris Rogers <crogers@google.com> wrote:
> > Hi Tom,
> > They are different API proposals.  The "Web Audio API" which I just wrote
> > about is described here:
> >
> http://chromium.googlecode.com/svn/trunk/samples/audio/specification/specification.html
> > Mozilla's proposal is called the "Audio Data API":
> > https://wiki.mozilla.org/Audio_Data_API
> > There has been a fair amount of discussion about the two approaches on
> this
> > list.  Here is my comparison:
> > Web Audio API
> > * implementations in WebKit - Google Chrome (Mac OS X only, but Windows
> and
> > Linux soon), Apple Safari
> > * high-level API - easy to do simple things like play sound now
> > * API is modular and scalable
> > * allows for the lowest possible latency - time between, for example, key
> > and mouse events and a sound being heard
> > * most of the implementation is in optimized assembly / C / C++ for
> > efficiency, so more can be done without bogging down the system
> > * more resistant to audio glitches / dropouts
> > * superset of Audio Data API functionality
> That's an unfair comparison: the Web Audio API is in no way shape or
> form a superset of the Audio Data API functionality. For one: it
> doesn't integrate with the Audio() API of the existing <audio> element
> of HTML5.

When I say "superset" I mean in functionality, not in the actual API itself.
 Put in other words, any application written using the Audio Data API should
be possible to write with the Web Audio API.

The Web Audio API *does* interact with the <audio> tag.  Please see:

And the diagram and example code here:

To be fair, I don't have the MediaElementSourceNode implemented yet, but I
do believe it's an important part of the specification.

> It also makes it really difficult to access individual audio
> samples and manipulate them.

I don't believe this is true.  Please see the section about

And try out the simple example (view source to see how simple the code is):

In particular the process() method is similar to the code which would be
used in the Audio Data API, and the approach taken is similar to that which
has been used for Flash audio.

> And finally, the Web Audio API only
> implements a certain set of audio manipulation functions in C/C++ - if
> a developer needs more flexibility, they have to use the JavaScript
> way here, too.

This is true, but I think the set of functions will be useful in a large set
of applications.  They can use custom JavaScript processing in special

> And, to be honest, to get to include a JavaScript
> function through the Web Audio API is rather complicated, while it's
> dead simple in the Audio Data API.

I disagree and have already responded about this in my response above
(talking about JavaScriptAudioNode).  I think it can even be argued that the
Mozilla API is harder to use as it often requires clunky code checking for
how much sample data is already buffered up.

> * more limited audio capabilities
> I'd argue the other way around: since you have access to the audio
> samples directly, the Audio Data API IMO has more flexible audio
> capabilities. Anything can be done once you have access to the samples
> directly.

First of all the Web Audio API also offers easy and direct access to the
samples similar to Flash and offering the same kind of low-level
manipulation as the Mozilla API.  Second, I think it's somewhat of an
overstatement to say that "anything" can be done because it glosses over
some very practical and real limitations like latency, audio breakup, and
scalability.  Developers are going to be faced with these issues in a very
practical sense.

> My description of the comparison is that the Audio Data API is a
> low-level API that allows direct access to samples and to manipulating
> them in JavaScript with your own features. It does require either a
> good JavaScript library or a good audio coder to achieve higher level
> functionality such as frequency transforms or filters. But it provides
> the sophisticated audio programmer with all the flexibility - alas
> with the drawback of having to do their own optimisation of code to
> achieve low latency.

I agree with most of this except the part about latency and JavaScript
optimization.  There are other factors at play having to do with threading,
garbage collection, etc. which make latency a nagging issue no matter how
much the JavaScript code is optimized.

> In comparison, the Web Audio API is built like traditional audio
> frameworks as a set of audio filters than can be composed together in
> a graph and then kicked off to let the browser take advantage of its
> optimised implementations of typical audio filters and achieve the
> required low latency. By providing a by nature limited set of audio
> filters, the audio programmer is restricted to combining these filters
> in a means that achieves their goals. If a required filter is not
> available, they can implement it in JavaScript and hook it into the
> filter graph.

I think that's pretty accurate, but I think in many (probably most)
applications it will never be necessary to write custom DSP code in
JavaScript since the provided filters have been proven in decades of use in
real-world audio applications to be very useful.

> In my opinion, the difference between the Web Audio API and the Audio
> Data API is very similar to the difference between SVG and Canvas. The
> Web Audio API is similar to SVG in that it provides "objects" that can
> be composed together to create a presentation. The Audio Data API is
> similar to Canvas in that it provides pixels to manipulate. Both have
> their use cases and community. So, similarly, I would hope that we can
> get both audio APIs into HTML5.

I've tried to incorporate the features of the Audio Data API into the Web
Audio API with the introduction of JavaScriptAudioNode
and MediaElementAudioSourceNode.  So, in a sense I believe we already have
the required features which you desire.

Received on Tuesday, 1 February 2011 23:05:45 UTC

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