Starting and stopping of local audio playback working through REST API

radio.py

@@ -3,6 +3,9 @@ import SoapySDR as soapy
 import prefixed
 from formats import *
 import sys
+import os
+import subprocess
+import struct
 
 
 class Radio:
@@ -11,9 +14,6 @@ class Radio:
 
     def __init__(self, device_info):
         self.device_info = device_info
-        self.stream = None
-        self.buffer = None
-        self.port = None
         self.run = False
         self.thread = None
 
@@ -21,7 +21,6 @@ class Radio:
         if self.device is None:
             raise RuntimeError("Failed to connect to radio device")
 
-
     def configure(self, frequency):
         frequency = int(prefixed.Float(frequency))
         sample_rate = 384000
@@ -41,31 +40,14 @@ class Radio:
             'gain-mode': 'auto' if self.device.getGainMode(soapy.SOAPY_SDR_RX, 0) else 'manual',
         }
 
-
     def start_stream(self):
         if self.thread:
             raise RuntimeError('Stream thread is already running')
 
-        self.buffer = np.array([0] * Radio.SAMPLES * 2, TYPES[Radio.FORMAT])
-        self.stream = self.device.setupStream(soapy.SOAPY_SDR_RX, FORMATS[Radio.FORMAT])
-        self.device.activateStream(self.stream)
-
         self.run = True
         self.thread = Thread(target=self._stream_thread, daemon=True, args=())
         self.thread.start()
 
-
-    def _stream_thread(self):
-        while self.run:
-            result = self.device.readStream(self.stream, [self.buffer], Radio.SAMPLES)
-
-            if result.ret < 1:
-                print('Stream read failed, exiting.', file=sys.stderr)
-                self.keep_going = False
-
-        self._cleanup_stream()
-
-
     def end_stream(self):
         if self.thread is None:
             raise RuntimeError('No stream thread to terminate')
@@ -74,8 +56,72 @@ class Radio:
         self.thread.join()
         self.thread = None
 
+    def _stream_thread(self):
+        self._init_stream()
+
+        while self.run:
+            result = self.device.readStream(self.stream, [self.buffer], Radio.SAMPLES)
+
+            if result.ret < 1:
+                print('Stream read failed, exiting.', file=sys.stderr)
+                self.keep_going = False
+
+            read_size = int(result.ret * 2)
+            self.demod.stdin.write(
+                struct.pack(PACKINGS[Radio.FORMAT] % read_size,
+                *self.buffer[:read_size])
+            )
+
+        self._cleanup_stream()
+
+    def _init_stream(self):
+        self.playback = subprocess.Popen(
+            ['/usr/bin/sox', '-t', 'raw', '-r', '32000', '-b', '16', '-c', '2', '-L', '-e', 'signed-integer', '-', '-d'],
+            stdin=subprocess.PIPE,
+            stdout=subprocess.DEVNULL,
+            stderr=subprocess.DEVNULL
+        )
+
+        self.demod = subprocess.Popen(
+            ['/usr/bin/python3', 'fm_demod.py', '-f', 'CS16', '-s', '384k', '-d', '32k'],
+            stdin=subprocess.PIPE,
+            stdout=self.playback.stdin,
+            stderr=subprocess.DEVNULL
+        )
+
+        self.buffer = np.array([0] * Radio.SAMPLES * 2, TYPES[Radio.FORMAT])
+        self.stream = self.device.setupStream(soapy.SOAPY_SDR_RX, FORMATS[Radio.FORMAT])
+        self.device.activateStream(self.stream)
 
     def _cleanup_stream(self):
-        #shutdown the stream
+        # Cleanup the streaming objects in the reverse order to the _init method.
         self.device.deactivateStream(self.stream)
-        self.device.closeStream(self.stream)
+        self.device.closeStream(self.stream)
+        self.buffer = None
+
+        self.demod.kill()
+        self.playback.kill()
+
+
+"""
+Quick and dirty test of the Radio class.
+"""
+if __name__ == '__main__':
+    import time
+
+    sdr = Radio({'driver': 'sdrplay'})
+
+    print('Configuring...')
+    sdr.configure('105.5M')
+    print('Configured.')
+
+    print('Starting stream...')
+    sdr.start_stream()
+    print('Stream started.')
+
+    # Let the stream play for a while
+    time.sleep(5)
+
+    print('Ending stream...')
+    sdr.end_stream()
+    print('Stream ended.')