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Re: Behavior of source nodes on connect/disconnect

From: Raymond Toy <rtoy@google.com>
Date: Thu, 12 Sep 2013 15:14:36 -0700
Message-ID: <CAE3TgXGCgdZ0JgMuZSpRVAAK3sRfx+ruLX6_Spa+oCE-TjcrGw@mail.gmail.com>
To: Chris Wilson <cwilso@google.com>
Cc: "public-audio@w3.org" <public-audio@w3.org>
On Thu, Sep 12, 2013 at 2:59 PM, Chris Wilson <cwilso@google.com> wrote:

> I believe the current understanding is that the nodes would all keep
> playing as if they were connected; that is:
>
> >If you have a (long) source node that has started playing and then you
> disconnect it (completely) after 1 sec from one part of the graph and then
> wait for, say, 1 sec, and connect it to a different (or same?) part of the
> graph, what should happen?
>
> You would "hear" it continue playing (so, from approximately 2 secs in to
> the source node content).
>

Agreed.


>
> >A different scenario:  You've started playing a source node, and then
> completely disconnect it from the graph and then add a onended listener.
>  What should happen? Does the onended listener get called when the source
> would normally end?
>
> If you've added an onended listener, that keeps the node alive, and it
> would fire when the node finished playing (despite it having been
> disconnected previously).
>

Agreed.


>
> >Another scenario:  Say you have a source node attached to a sub graph
> that isn't currently attached to the destination.  If you start(0) the
> source node, and then later on connect the subgraph to the destination,
> what should happen?
>
> It "continues" from wherever it is in playback when you connect() it.
>  That includes time side effects - e.g. if the subgraph includes a
> convolution or delay node, those effects from previous data would be
> applied.
>

Hmm.  I agree in principle, but this is somewhat problematic in Chrome
today, I think.  More thinking needed.


>
> >Or say you don't connect the subgraph, but have an onended listener for
> the source.  The listener should get fired, once the source is started?
>
> Once the source has finished, yes.  (if the source is a 5 second buffer,
> you would get onended fired approximately 5 seconds after start(0) is
> called.)
>
>
Agreed.


> This model is akin to plugging patch cords between nodes, which I've
> always found the most intuitive from a developer perspective; Chris
> disagreed with me on this for quite a while, but I think he'd come around.
>

The patch cord idea is very intuitive.  I think the implementation in
Blink, however, is a bit troublesome since the destination pulls on the
graph to get data, and if a cord is not connected, it never gets pulled.
I'm not sure how to do this effectively.

Does the spec imply that this is how it works? I couldn't find anything
definitive.

>
> -Chris
>
>
> On Thu, Sep 12, 2013 at 2:46 PM, Raymond Toy <rtoy@google.com> wrote:
>
>> Another scenario:  Say you have a source node attached to a sub graph
>> that isn't currently attached to the destination.  If you start(0) the
>> source node, and then later on connect the subgraph to the destination,
>> what should happen?
>>
>> Or say you don't connect the subgraph, but have an onended listener for
>> the source.  The listener should get fired, once the source is started?
>>
>>
>> On Thu, Sep 12, 2013 at 1:51 PM, Raymond Toy <rtoy@google.com> wrote:
>>
>>> While fixing a different issue in Chrome's webaudio, the following
>>> questions came up.
>>>
>>> If you have a (long) source node that has started playing and then you
>>> disconnect it (completely) after 1 sec from one part of the graph and then
>>> wait for, say, 1 sec, and connect it to a different (or same?) part of the
>>> graph, what should happen?  Does the node start playing again?  What does
>>> it play? The source starting at time 2 sec?
>>>
>>> A different scenario:  You've started playing a source node, and then
>>> completely disconnect it from the graph and then add a onended listener.
>>>  What should happen? Does the onended listener get called when the source
>>> would normally end?
>>>
>>> I think these are not scenarios that would normally occur, but it came
>>> up during a review, and I didn't know the answer.
>>>
>>> Help!
>>>
>>> Ray
>>>
>>>
>>
>
Received on Thursday, 12 September 2013 22:15:04 UTC

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