Audio widget uses numpy array and sample_rate as input (#703)

examples/reference/widgets/Audio.ipynb

@@ -6,7 +6,9 @@
    "metadata": {},
    "outputs": [],
    "source": [
+    "import numpy as np\n",
     "import panel as pn\n",
+    "\n",
     "pn.extension()"
    ]
   },
@@ -33,13 +35,51 @@
     "___"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "The `Audio` widget can be constructed with a URL pointing to a remote audio file or a local audio file (in which case the data is embedded)."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "pn.widgets.Audio(name='Audio', value='http://ccrma.stanford.edu/~jos/mp3/pno-cs.mp3')"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Alternatively, if SciPy is available, the widget may also be constructed from a NumPy array containing int16 values and a `sample_rate`, e.g. in this example we plot a frequency modulated signal:"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
-    "audio = pn.widgets.Audio(name='Audio', value='http://ccrma.stanford.edu/~jos/mp3/pno-cs.mp3')\n",
+    "sps = 44100 # Samples per second\n",
+    "duration = 10 # Duration in seconds\n",
+    "\n",
+    "modulator_frequency = 2.0\n",
+    "carrier_frequency = 120.0\n",
+    "modulation_index = 2.0\n",
+    "\n",
+    "time = np.arange(sps*duration) / sps\n",
+    "modulator = np.sin(2.0 * np.pi * modulator_frequency * time) * modulation_index\n",
+    "carrier = np.sin(2.0 * np.pi * carrier_frequency * time)\n",
+    "waveform = np.sin(2. * np.pi * (carrier_frequency * time + modulator))\n",
+    "    \n",
+    "waveform_quiet = waveform * 0.3\n",
+    "waveform_int = np.int16(waveform_quiet * 32767)\n",
+    "\n",
+    "audio = pn.widgets.Audio(value=waveform_int, sample_rate=sps)\n",
     "audio"
    ]
   },
@@ -99,5 +139,5 @@
   }
  },
  "nbformat": 4,
- "nbformat_minor": 2
+ "nbformat_minor": 4
 }

panel/tests/widgets/test_misc.py

@@ -0,0 +1,32 @@
+from __future__ import absolute_import, division, unicode_literals
+
+from io import BytesIO
+from base64 import b64encode
+
+import numpy as np
+from scipy.io import wavfile
+
+from panel.widgets import Audio
+
+def test_audio_array(document, comm):
+    data = np.random.randint(-100,100, 100).astype('int16')
+    sample_rate = 10
+    buffer = BytesIO()
+    wavfile.write(buffer, sample_rate, data)
+    b64_encoded = b64encode(buffer.getvalue()).decode('utf-8')
+
+    audio = Audio(name='Button', value=data, sample_rate=sample_rate)
+    widget = audio.get_root(document, comm=comm)
+    widget_value = widget.value
+
+    assert widget_value.split(',')[1] == b64_encoded
+    assert widget.value.startswith('data:audio/wav;base64')
+
+
+def test_audio_url(document, comm):
+    audio_url = 'http://ccrma.stanford.edu/~jos/mp3/pno-cs.mp3'
+    audio2 = Audio(name='Audio', value=audio_url)
+    url_widget = audio2.get_root(document, comm=comm)
+
+    assert audio_url == url_widget.value
+

panel/widgets/misc.py

@@ -5,9 +5,13 @@
 
 import os
 
+from io import BytesIO
 from base64 import b64encode
+from six import string_types
 
 import param
+import numpy as np
+from scipy.io import wavfile
 
 from ..io.notebook import push
 from ..io.state import state
@@ -30,29 +34,51 @@ class Audio(Widget):
     paused = param.Boolean(default=True, doc="""
         Whether the audio is currently paused""")
 
-    value = param.String(default='', doc="""
+    sample_rate = param.Integer(default=44100, doc="""
+        The sample_rate of the audio when given a NumPy array.""")
+
+    value = param.ClassSelector(default='', class_=(string_types + (np.ndarray,)), doc="""
         The audio file either local or remote.""")
 
     volume = param.Number(default=None, bounds=(0, 100), doc="""
         The volume of the audio player.""")
 
     _widget_type = _BkAudio
 
-    _rename = {'name': None}
+    _rename = {'name': None, 'sample_rate': None}
+
+    def _from_numpy(self, data):
+        buffer = BytesIO()
+        wavfile.write(buffer, self.sample_rate, data)
+        return buffer
 
     def _process_param_change(self, msg):
         msg = super(Audio, self)._process_param_change(msg)
-        if 'value' in msg and os.path.isfile(msg['value']):
-            fmt = msg['value'].split('.')[-1]
-            with open(msg['value'], 'rb') as f:
-                data = f.read()
+
+        if 'value' in msg:
+            value =  msg['value']
+            if isinstance(value, np.ndarray):
+                fmt = 'wav'
+                buffer = self._from_numpy(value)
+                data = b64encode(buffer.getvalue())
+            elif os.path.isfile(value):
+                fmt = value.split('.')[-1]
+                with open(value, 'rb') as f:
+                    data = f.read()
+                data = b64encode(data)
+            elif value.lower().startswith('http'):
+                return msg
+            elif not value:
+                data, fmt = b'', 'wav'
+            else:
+                raise ValueError('Value should be either path to a sound file or numpy array')
             template = 'data:audio/{mime};base64,{data}'
-            data = b64encode(data)
             msg['value'] = template.format(data=data.decode('utf-8'),
                                            mime=fmt)
         return msg
 
 
+
 class VideoStream(Widget):
 
     format = param.ObjectSelector(default='png', objects=['png', 'jpeg'],