How To Export Last 3s Data Of A Web Audio Stream

Question: I am using web audio API. I need to buffer a non-stop audio stream, like a radio stream. and when I get a notification, I need to get the past 3s audio data and send it t

Solution 1:

You can capture the audio from a stream using the ScriptProcessorNode. Whilst this is deprecated no browser as of now actually implements the new AudioWorker.

varN=1024;
vartime=3; // Desired time of capture;varframe_holder= [];
vartime_per_frame= N / context.sampleRate;
varnum_frames= Math.ceil(time / time_per_frame); // Minimum number to meet timevarscript= context.createScriptProcessor(N,1,1);
script.connect(context.destination);

script.onaudioprocess = function(e) {
  varinput= e.inputBuffer.getChannelData(0);
  varoutput= e.outputBuffer.getChannelData(0);
  varcopy=newFloat32Array(input.length);
  for (var n=0; n<input.length; n++) {
    output[n] = 0.0; // Null this as I guess you are capturing microphone
    copy[n] = input[n];
  }
  // Now we need to see if we have more than 3s worth of framesif (frame_holder.length > num_frames) {
    frame_holder = frame_holder.slice(frame_holder.length-num_frames);
  }
  // Add in the current framevartemp= frame_holder.slice(1); // Cut off first frame;
  frame_holder = temp.concat([copy]); // Add the latest frame
}

Then for actual transmission, you just need to string the copied frames together. It is easier than trying to keep one long array though of course that is also possible.