Add channel parameter for drawing specified channel

src/drawer.canvas.js

@@ -73,6 +73,11 @@ WaveSurfer.util.extend(WaveSurfer.Drawer.Canvas, {
                 this.setHeight(channels.length * this.params.height * this.params.pixelRatio);
                 channels.forEach(this.drawBars, this);
                 return;
+            } else if (this.params.channel > -1) { // Channel specified
+                if (this.params.channel >= channels.length) {
+                    throw new error('Channel doesn\'t exist');
+                }
+                peaks = channels[this.params.channel];
             } else {
                 peaks = channels[0];
             }
@@ -126,6 +131,11 @@ WaveSurfer.util.extend(WaveSurfer.Drawer.Canvas, {
                 this.setHeight(channels.length * this.params.height * this.params.pixelRatio);
                 channels.forEach(this.drawWave, this);
                 return;
+            } else if (this.params.channel > -1) { // Channel specified
+                if (this.params.channel >= channels.length) {
+                    throw new error('Channel doesn\'t exist');
+                }
+                peaks = channels[this.params.channel];
             } else {
                 peaks = channels[0];
             }

src/wavesurfer.js

@@ -29,6 +29,7 @@ var WaveSurfer = {
         audioRate     : 1,
         interact      : true,
         splitChannels : false,
+        channel       : -1,
         mediaContainer: null,
         mediaControls : false,
         renderer      : 'Canvas',
@@ -296,6 +297,12 @@ var WaveSurfer = {
         this.fireEvent('zoom', pxPerSec);
     },
 
+    setChannel: function (channel) {
+        this.params.channel = channel;
+        this.drawer.clearWave();
+        this.drawBuffer();
+    },
+
     /**
      * Internal method.
      */

src/webaudio.js

@@ -225,7 +225,7 @@ WaveSurfer.WebAudio = {
             }
         }
 
-        return this.params.splitChannels ? splitPeaks : mergedPeaks;
+        return (this.params.splitChannels || this.params.channel > -1) ? splitPeaks : mergedPeaks;
     },
 
     getPlayedPercents: function () {