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Re: Reviewing the Web Audio API (from webrtc)

From: Randell Jesup <randell-ietf@jesup.org>
Date: Tue, 10 Apr 2012 16:21:31 -0400
Message-ID: <4F84964B.2020005@jesup.org>
To: public-audio@w3.org
>On Thu, Mar 29, 2012 at 6:32 PM, Chris Rogers<crogers@google.com  <mailto:crogers@google.com?Subject=Re%3A%20Reviewing%20the%20Web%20Audio%20API%20%28from%20webrtc%29&In-Reply-To=%253CCAOp6jLa4UShFqAeOqWHFj8w0VfMWOoMGM5kstmUDQqJEMGa%2BOA%40mail.gmail.com%253E&References=%253CCAOp6jLa4UShFqAeOqWHFj8w0VfMWOoMGM5kstmUDQqJEMGa%2BOA%40mail.gmail.com%253E>>  wrote:
>
>>  None of the built-in Web Audio processing algorithms have any appreciable
>>  latency which would perceptibly affect audio/video sync.
>
>
>OK, but there are processing algorithms that necessarily have significant
>latency, like this one:
>  http://people.mozilla.org/~roc/stream-demos/video-with-extra-track-and-effect.html  <http://people.mozilla.org/%7Eroc/stream-demos/video-with-extra-track-and-effect.html>
>
>>  We're talking about 3ms or less here.  In terms of irritation, network
>>  latency is of vastly more concern for WebRTC applications.
>
>  That depends on the application. WebRTC APIs can be used for more than just
>  interactive chat. For example, an application could pull an audio and video
>  stream from some source, take a user's commentary in a stream from the
>  microphone, mix them with a ducking effect, and stream the resulting audio
>  and video out to a set of peers. The latency might be too high for
>  interaction, but just fine for a "live broadcast".

Another example is an AGC, Dynamic Range Compressor, or Limiter using a look-ahead
to avoid having to use extreme attack values.  This could induce 5, 10 or more ms
of delay.  An extreme version of look-ahead is Rob's "ducking" example for doing
voice-overs, where you might have 1/4, 1/2 or 1 second delay.

Random example of a look-ahead filter:
http://forum.audacityteam.org/viewtopic.php?p=162765

-- 
Randell Jesup
randell-ietf@jesup.org
Received on Tuesday, 10 April 2012 20:25:45 GMT

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