[setPlaybackRate] Webaudio backend fix (katspaugh#2118)

* [setPlaybackRate]
webaudio backend: set playback rate modifying directly the playback property of the source node. Removed invocation to pause and play

* [setPlaybackRate]
webaudio backend: check if source node not null

* [setPlaybackRate]
changelog

CHANGES.md

@@ -5,6 +5,7 @@ wavesurfer.js changelog
 ------------------
 
 - Add `relativeNormalization` option to maintain proportionality between waveforms when `splitChannels` and `normalize` are `true` (#2108)
+- WebAudio backend: set playback rate modifying directly the playback property of the source node (#2118)
 - Spectrogram plugin: Use `ImageData` to draw pixel-by-pixel (#2127)
 
 4.2.0 (20.10.2020)

src/webaudio.js

@@ -576,10 +576,7 @@ export default class WebAudio extends util.Observer {
         this.source.start = this.source.start || this.source.noteGrainOn;
         this.source.stop = this.source.stop || this.source.noteOff;
 
-        this.source.playbackRate.setValueAtTime(
-            this.playbackRate,
-            this.ac.currentTime
-        );
+        this.setPlaybackRate(this.playbackRate);
         this.source.buffer = this.buffer;
         this.source.connect(this.analyser);
     }
@@ -736,14 +733,11 @@ export default class WebAudio extends util.Observer {
      * @param {number} value The playback rate to use
      */
     setPlaybackRate(value) {
-        value = value || 1;
-        if (this.isPaused()) {
-            this.playbackRate = value;
-        } else {
-            this.pause();
-            this.playbackRate = value;
-            this.play();
-        }
+        this.playbackRate = value || 1;
+        this.source && this.source.playbackRate.setValueAtTime(
+            this.playbackRate,
+            this.ac.currentTime
+        );
     }
 
     /**