Fixed waveform rescaling

The WaveformZoomView _scale value must always match
the scale of the WaveformData object, which can
only be integer.

See #513

src/waveform-zoomview.js

@@ -305,7 +305,7 @@ WaveformZoomView.prototype._syncPlayhead = function(time) {
 };
 
 WaveformZoomView.prototype._getScale = function(duration) {
-  return duration * this._data.sample_rate / this._width;
+  return Math.floor(duration * this._data.sample_rate / this._width);
 };
 
 function isAutoScale(options) {
@@ -348,7 +348,7 @@ WaveformZoomView.prototype.setZoom = function(options) {
   else {
     if (objectHasProperty(options, 'scale')) {
       this._zoomLevelSeconds = null;
-      scale = options.scale;
+      scale = Math.floor(options.scale);
     }
     else if (objectHasProperty(options, 'seconds')) {
       if (!isValidTime(options.seconds)) {

test/api-view-spec.js

@@ -210,6 +210,24 @@ describe('WaveformView', function() {
           });
         });
 
+        context('with non-integer scale', function() {
+          it('should round the scale down to an integer value', function() {
+            const view = p.views.getView('zoomview');
+
+            const resampleData = sinon.spy(view, '_resampleData');
+
+            view.setZoom({ scale: 500.5 });
+
+            expect(resampleData.callCount).to.equal(1);
+
+            // width is here because WaveformData.resample modifies
+            // its options parameter
+            expect(resampleData).calledWithExactly({ scale: 500, width: null });
+
+            expect(view._scale).to.equal(500);
+          });
+        });
+
         context('with auto option', function() {
           it('should fit the waveform to the width of the view', function() {
             const view = p.views.getView('zoomview');