Add play_stream.py example

Author: mgeier

doc/examples.rst

@@ -14,6 +14,13 @@ Play a Very Long Sound File
 
 .. literalinclude:: ../examples/play_long_file.py
 
+Play a Web Stream
+-----------------
+
+:download:`play_stream.py <../examples/play_stream.py>`
+
+.. literalinclude:: ../examples/play_stream.py
+
 Play a Sine Signal
 ------------------
 

examples/play_stream.py

@@ -0,0 +1,125 @@
+#!/usr/bin/env python3
+"""Play a web stream.
+
+ffmpeg-python (https://github.com/kkroening/ffmpeg-python) has to be installed.
+
+If you don't know a stream URL, try http://icecast.spc.org:8000/longplayer
+(see https://longplayer.org/ for a description).
+
+"""
+import argparse
+import queue
+import sys
+
+import ffmpeg
+import sounddevice as sd
+
+
+def int_or_str(text):
+    """Helper function for argument parsing."""
+    try:
+        return int(text)
+    except ValueError:
+        return text
+
+
+parser = argparse.ArgumentParser(add_help=False)
+parser.add_argument(
+    '-l', '--list-devices', action='store_true',
+    help='show list of audio devices and exit')
+args, remaining = parser.parse_known_args()
+if args.list_devices:
+    print(sd.query_devices())
+    parser.exit(0)
+parser = argparse.ArgumentParser(
+    description=__doc__,
+    formatter_class=argparse.RawDescriptionHelpFormatter,
+    parents=[parser])
+parser.add_argument(
+    'url', metavar='URL',
+    help='stream URL')
+parser.add_argument(
+    '-d', '--device', type=int_or_str,
+    help='output device (numeric ID or substring)')
+parser.add_argument(
+    '-b', '--blocksize', type=int, default=1024,
+    help='block size (default: %(default)s)')
+parser.add_argument(
+    '-q', '--buffersize', type=int, default=20,
+    help='number of blocks used for buffering (default: %(default)s)')
+args = parser.parse_args(remaining)
+if args.blocksize == 0:
+    parser.error('blocksize must not be zero')
+if args.buffersize < 1:
+    parser.error('buffersize must be at least 1')
+
+q = queue.Queue(maxsize=args.buffersize)
+
+print('Getting stream information ...')
+
+try:
+    info = ffmpeg.probe(args.url)
+except ffmpeg.Error as e:
+    sys.stderr.buffer.write(e.stderr)
+    parser.exit(e)
+
+streams = info.get('streams', [])
+if len(streams) != 1:
+    parser.exit('There must be exactly one stream available')
+
+stream = streams[0]
+
+if stream.get('codec_type') != 'audio':
+    parser.exit('The stream must be an audio stream')
+
+channels = stream['channels']
+samplerate = float(stream['sample_rate'])
+
+
+def callback(outdata, frames, time, status):
+    assert frames == args.blocksize
+    if status.output_underflow:
+        print('Output underflow: increase blocksize?', file=sys.stderr)
+        raise sd.CallbackAbort
+    assert not status
+    try:
+        data = q.get_nowait()
+    except queue.Empty:
+        print('Buffer is empty: increase buffersize?', file=sys.stderr)
+        raise sd.CallbackAbort
+    assert len(data) == len(outdata)
+    outdata[:] = data
+
+
+try:
+    print('Opening stream ...')
+    process = ffmpeg.input(
+        args.url
+    ).output(
+        'pipe:',
+        format='f32le',
+        acodec='pcm_f32le',
+        ac=channels,
+        ar=samplerate,
+        loglevel='quiet',
+    ).run_async(pipe_stdout=True)
+    stream = sd.RawOutputStream(
+        samplerate=samplerate, blocksize=args.blocksize,
+        device=args.device, channels=channels, dtype='float32',
+        callback=callback)
+    read_size = args.blocksize * channels * stream.samplesize
+    print('Buffering ...')
+    for _ in range(args.buffersize):
+        q.put_nowait(process.stdout.read(read_size))
+    print('Starting Playback ...')
+    with stream:
+        timeout = args.blocksize * args.buffersize / samplerate
+        while True:
+            q.put(process.stdout.read(read_size), timeout=timeout)
+except KeyboardInterrupt:
+    parser.exit('\nInterrupted by user')
+except queue.Full:
+    # A timeout occurred, i.e. there was an error in the callback
+    parser.exit(1)
+except Exception as e:
+    parser.exit(type(e).__name__ + ': ' + str(e))