working first block

apps/casette/encode.py

@@ -20,6 +20,11 @@ class FSKWriter:
         self.phase = 0.0
         self.samples = bytearray()
 
+        self.samples.extend(b'\0'*int(1.0*self.sample_rate))
+
+    def finalize(self):
+        self.samples.extend(b'\0'*int(1.0*self.sample_rate))
+
     def _tone(self, frequency: float, sample_count: int) -> None:
         phase_step = 2.0 * math.pi * frequency / self.sample_rate
         scale = int(32767 * self.amplitude)
@@ -41,7 +46,7 @@ class FSKWriter:
         for _ in range(8):
             self.bit(1)
             self.bit(0)
-        self.byte(0x0f)
+        self.byte(0xf0)
 
     def bit(self, value: int) -> None:
         if value:
@@ -66,6 +71,7 @@ class FSKWriter:
         self.byte(l&0xff)
         self.bytes(data)
         self.byte(self.chsum(data))
+        self.samples.extend(b'\0'*int(0.3*self.sample_rate))
 
     def chsum(self, data: bytes) -> int:
         cs = 0
@@ -93,6 +99,7 @@ def main() -> None:
     tones.block(0, args.input.name.encode())
 
 
+    tones.finalize()
     with wave.open(str(output_path), "wb") as wav:
         wav.setnchannels(1)
         wav.setsampwidth(2)