Add priming_output example

Author: mgeier

examples/priming_output.py

@@ -0,0 +1,27 @@
+#!/usr/bin/env python3
+"""Test priming output buffer.
+
+See http://www.portaudio.com/docs/proposals/020-AllowCallbackToPrimeStream.html
+
+Note that this is only supported in some of the host APIs.
+
+"""
+import sounddevice as sd
+
+
+def callback(indata, outdata, frames, time, status):
+    outdata.fill(0)
+    if status.priming_output:
+        assert status.input_underflow, 'input underflow flag should be set'
+        assert not indata.any(), 'input buffer should be filled with zeros'
+        print('Priming output buffer!')
+        outdata[0] = 1
+    else:
+        print('Not priming, I quit!')
+        raise sd.CallbackStop
+
+
+with sd.Stream(channels=2, callback=callback,
+               prime_output_buffers_using_stream_callback=True) as stream:
+    while stream.active:
+        sd.sleep(100)