visualize mediastream which is coming from a remote peer connection

问题

Since some days I`m trying to visualize an audiostream which is coming over webrtc. We already wrote some visuals which are working fine for the normal local stream (webaudio microphone usage).

Then I found some really interesting things on https://github.com/muaz-khan/WebRTC-Experiment/tree/master/ for streaming the microphone input between different browsers. We need this to have the same audio data from one backend for all clients in the frontend.

Everything works fine and some tests showed that we can hear each other. So I thought that it is also not a problem to visualize the incoming stream.

But: all frequency data are empty (zero), even if we can hear each other.

Does anybody has a solution or hint for this? Thanks in advance!

This is my test for analysing the remote frequence data:

include these files first:

webrtc-experiment.com/firebase.js

webrtc-experiment.com/one-to-many-audio-broadcasting/meeting.js

        var meeting = new Meeting('test');
        var audioContext = new window.webkitAudioContext();
        var analyser = audioContext.createAnalyser();

        // on getting local or remote streams
        meeting.onaddstream = function(e) {
            console.log(e.type);
            console.log(e.audio);
            console.log(e.stream);

            if(e.type === 'local')
            {
                //try it with the local stream, it works!
            }
            else
            {

                var source = audioContext.createMediaStreamSource(e.stream);

                source.connect(analyser);
                analyser.connect(audioContext.destination);

                console.log(analyser.fftSize);
                console.log(analyser.frequencyBinCount);

                analyser.fftSize = 64;
                console.log(analyser.frequencyBinCount);

                var frequencyData = new Uint8Array(analyser.frequencyBinCount);
                analyser.getByteFrequencyData(frequencyData);

                function update() {
                    requestAnimationFrame(update);

                    analyser.getByteFrequencyData(frequencyData);

                    console.log(frequencyData);
                };

                update();
            }
        };

        meeting.check();
        meeting.setup('test');

回答1:

I found a simple "solution" at least for the next time:

I have plugged a male / male audio cable from microphone to headphone in all my clients. Then I read the local microphone stream and, what a miracle, i can visualize what Im hearing.

Not a good solution, but it`s doing the job..

One Question: Is it possible to re-grab the destination as a stream in javascript? Then I would not need the audio cables..

回答2:

Note that analysing remote streams should work for Firefox and it is known to not to work in Chrome, see http://code.google.com/p/chromium/issues/detail?id=241543

A possible workaround could be taking the remote audio level value by using WebRTC statistics API.

If you go to chrome://webrtc-internals/ then select your page playing remote stream then one of the ssrc_XXXX_recv will contain dynamically changing audioOutputLevel value which you can use.

You can access the value using Chrome PeerConnection's statistics API, specifically, getStats() method.

A possible downside may be that this is the value of actual sound the user hears from the video/audio element, so if the user mutes or changes volume of the media element, it will affect the audioOutputLevel value.

Good luck! :-)

来源：https://stackoverflow.com/questions/19950937/visualize-mediastream-which-is-coming-from-a-remote-peer-connection