Re: The Volume issue - a suggestion to remove it from scope

i second silvia there, remote streams received through a peer connection
cannot be manipulated that way for now.


On Wed, Dec 11, 2013 at 6:15 PM, Silvia Pfeiffer
<silviapfeiffer1@gmail.com>wrote:

> I'm happy with that add long as you can fix the chrome bug that doesn't
> expose an audio data api on peer streams!
>
> Silvia.
> On 11 Dec 2013 20:26, "Harald Alvestrand" <harald@alvestrand.no> wrote:
>
>> One of the irritating things in the stats and media discussion has been
>> the question of "audio volume".
>>
>> There are many apps that need it, yet defining the term has proved
>> surprisingly slippery - what is it we measure, what's the baseline, do we
>> need psychometric shaping of the signal before measuring it, what time
>> scale does it need to be integrated over, and so on and so forth.
>>
>> At the moment, there is a stat in the Chrome implementation called
>> "audioVolume" that has no particular definition, and has proved troublesome
>> in multiple ways (for instance, it's not available without linking the
>> track to an active PeerConnection).
>>
>> The suggestion has been made to expose a property on a MediaStreamTrack
>> instead - but that runs into all the previously mentioned issues.
>>
>> But there is another way: Use WebAudio. Get the samples. Let the
>> application decide.
>>
>> I created a demo, which works both in Firefox and Chrome, here:
>>
>> https://webrtc.googlecode.com/svn/trunk/samples/js/demos/
>> html/local-audio-volume.html
>>
>> The essential part of the code is reproduced below, it's not long.
>> I believe that:
>>
>> - This shows that volume can be measured in an application, from a
>> MediaStreamTrack, without any modification to any part of the Media Capture
>> and Streams spec.
>>
>> - This shows that the application can control the definition of "volume"
>> to be exactly what it wants it to be; again, without making any change to
>> any part of the Media Capture And Streams spec.
>>
>> - This shows that the cost is a Javascript invocation every 50 ms, where
>> the heaviest operation is a square root. People can test for themselves if
>> this matters for the devices they are concerned about.
>>
>> Therefore, on the principle that we should not solve a problem twice, I
>> propose that we declare the problem of "measuring the volume of an audio
>> track" to be out of scope for the working group.
>>
>> Does this make sense for people?
>>
>>             Harald
>>
>>
>>   // Meter class that generates a number correlated to audio volume.
>>   // The meter class itself displays nothing, but it makes the
>>   // instantaneous and time-decaying volumes available for inspection.
>>   // It also reports on the fraction of samples that were at or near
>>   // the top of the measurement range.
>>   function SoundMeter(context) {
>>     this.context = context
>>     this.volume = 0.0;
>>     this.slow_volume = 0.0;
>>     this.clip = 0.0;
>>     this.script = context.createScriptProcessor(2048, 1, 1);
>>     that = this;
>>     this.script.onaudioprocess = function(event) {
>>       var input = event.inputBuffer.getChannelData(0);
>>       var i;
>>       var sum = 0.0;
>>       var clipcount = 0;
>>       for (i = 0; i < input.length; ++i) {
>>         sum += input[i] * input[i];
>>         if (Math.abs(input[i]) > 0.99) {
>>           clipcount += 1
>>         }
>>       }
>>       that.volume = Math.sqrt(sum / input.length);
>>       that.slow_volume = 0.95 * that.slow_volume + 0.05 * that.volume;
>>       that.clip = clipcount / input.length;
>>     }
>>   }
>>
>>   SoundMeter.prototype.connectToSource = function(stream) {
>>     console.log('SoundMeter connecting');
>>     this.mic = this.context.createMediaStreamSource(stream);
>>     this.mic.connect(this.script);
>>     // Necessary to make sample run, but should not be.
>>     this.script.connect(this.context.destination);
>>   }
>>
>>   SoundMeter.prototype.stop = function() {
>>     this.mic.disconnect();
>>     this.script.disconnect();
>>   }
>>
>>   // End of SoundMeter class.
>>
>>
>>