Output some silence before signal (useful because some audio cards does output garbage at start of playback)

decode.py

@@ -34,7 +34,8 @@ DESCRIPTION = 'Decodes a file using the manchester encoding'
 
 FRAME_DELIMITER = 126 # (01111110)
 FRAME_DELIMITER_EVERY_BYTES = 64
-PREAMBLE_DURATION = 512
+# Clock signal duration peceding effective signal
+PREAMBLE_DURATION = 1280
 # Values nearest to zero than this are not considered: set to more than noise, less than signal
 AUDIO_MIN_VOLUME = 12288
 # The 0 value: values less than this are considered 0, more than this 1. This should be
@@ -63,6 +64,8 @@ class Main:
 				self.decodeActualData()
 			except ValueError as e:
 				self._log.error("Ran out of input data before completing initialization!")
+			except struct.error as e:
+				self._log.error("Unsupported wav format: only mono PCM is supported")
 
 		self.audioSource.close()
 		self.outputSink.close()

encode.py

@@ -34,7 +34,10 @@ DESCRIPTION = 'Encodes a file using the manchester encoding and outputs it as au
 
 FRAME_DELIMITER = 126 # (01111110)
 FRAME_DELIMITER_EVERY_BYTES = 64
-PREAMBLE_DURATION = 512
+# Seconds of preceding silence (useful because some audio cards does output garbage at start of playback)
+PRECEDING_SILENCE_SECS = 2
+# Clock signal duration peceding effective signal
+PREAMBLE_DURATION = 1280
 AUDIO_VOLUME = 16384 # 0 to 32767
 AUDIO_BITRATE = 44100
 
@@ -58,6 +61,9 @@ class Main:
 		self.audioSink.setsampwidth(2)
 		self.audioSink.setframerate(44100.0)
 
+		# Silence
+		self.outputSilence()
+
 		# Preamble
 		self.outputPreamble()
 
@@ -109,6 +115,11 @@ class Main:
 				self.encodeBit(0)
 				consecutiveOnes = 0
 
+	def outputSilence(self):
+		# A second of silence preceeding signal
+		for x in range(AUDIO_BITRATE * PRECEDING_SILENCE_SECS):
+			self.audioSink.writeframesraw(struct.pack('<h', 0))
+
 	def outputPreamble(self):
 		# Outputs the preable: a sequence of 64 "1" and "0" used to facilitate the receiver
 		# syncronizing on our clock. The sequence starts with 1 and ends with 0