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Re: Web Audio API Spec

From: Ian Ni-Lewis <ilewis@google.com>
Date: Mon, 20 Jun 2011 09:51:37 -0700
Message-ID: <BANLkTin214EHRB37oFnTzWAyHi_mM8c6hWuyXKaw=D-4a_JF5g@mail.gmail.com>
To: Jussi Kalliokoski <jussi.kalliokoski@gmail.com>
Cc: public-audio@w3.org
Responses inline...

On Mon, Jun 20, 2011 at 1:06 AM, Jussi Kalliokoski <
jussi.kalliokoski@gmail.com> wrote:

> First of all, the spec is way too non-specific. For example, if the spec
> says "a more advanced implementation could", that just gives too much
> freedom to implementations, and can result in serious pain to web
> developers. Say, some implementation decides not to implement a delay node,
> so if your application requires that behaviour, you have to have a pure js
> implementation and feature detection in place to counter that, and that just
> beats the purpose of having a higher level API.
>

I think this is a valid point, if what you're asking for is a minimum set of
supported nodes. Implementations should be allowed to support additional
nodes through the same extension mechanisms that are currently used in other
specs such as HTML and CSS.


>
> The next thing is somewhat the same thing, this is also something that I've
> confirmed in my discussions with people. Currently the spec doesn't specify
> the exact algorithms to use with the processing of the nodes.
>

Very good point. We should specify this.


> Also, the current spec is very much wrong in a way that... It let's the
> implementation mandate the spec and not vice versa, and that is just not
> acceptable from my point of view, and that is also confirmed in my
> discussions. An example of this is that when you create a pure javascript
> processing thingy, as far as I know, you can't know for sure that you would
> get the buffer size and sample rate that you asked for.
>

This doesn't seem like the implementation mandating the spec; it seems like
an acknowledgement of varying target HW platforms. To give another example,
the HTML spec allows the "implementation" to "mandate" the size of the
display. I don't think this is because the spec is being heavy-handed; I
think it's because in the real world people run their browsers at many
different widths and heights, and it's useful for developers to know at what
resolution the user has chosen to view the page. It's possible, of course,
to let the web page mandate a logical resolution and force the browser to
resample the page to fit in the user's window, but that seldom produces
optimal results.


> I think this is also not a very good idea, if we have a higher level API
> like this, it should be able to do the resampling for you, otherwise you may
> have to do it in JS, which is a performance hit and often a nasty hack. I
> think that the spec should state that IFF the sample rate and buffer size
> aren't specified, the implementation tries to find the optimal values for
> them.
>

What puzzles me about this argument is the assumption that the JS would need
to resample. Most of the processing I'd envision doing is more or less
sample rate independent, in the sense that the sample rate is a free
variable in the processing function. It's trivial, for instance, to generate
a sine wave or perform filtering at any arbitrary sample rate.

Buffer size is a little less flexible, given that you may have for instance
an FFT that requires a specific buffer size to operate. But rebuffering the
data isn't nearly as expensive as resampling, and doing it in JS doesn't
seem like a particularly bad idea.

On the other hand, if we allowed JS to demand a specific sample rate, then
the implementation would be forced to resample twice--once on the way in,
once on the way out--and perform extra buffering. This imposes a cost
without a clear benefit. In fact, it's quite possible that quality would
suffer.

Perhaps you could clarify the sorts of processing you had in mind, where JS
would be unable to deal with arbitrary sample rates and buffer sizes.

Thanks
Ian


> I hope that we can raise a good discussion regarding these problems.
>
> Jussi
>



-- 
Ian Ni-Lewis
Developer Advocate
Google Game Developer Relations
Received on Monday, 20 June 2011 16:52:31 GMT

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