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

+1 to not re-inventing WebAudio stuff like this

roBman


On 11/12/13 8:25 PM, Harald Alvestrand 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.
>
>
>

Received on Wednesday, 11 December 2013 22:36:43 UTC