43 lines
1.5 KiB
Python
43 lines
1.5 KiB
Python
 
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"""Writes a test LTC file (biphase mark, 30 fps, 48 kHz) for ltc_listen.swift's decoder test."""
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import struct
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import sys
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import wave
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def frame_bits(h, m, s, f):
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bits = [0] * 80
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def put(v, at, n):
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for i in range(n):
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bits[at + i] = (v >> i) & 1
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put(f % 10, 0, 4); put(f // 10, 8, 2); put(s % 10, 16, 4); put(s // 10, 24, 3)
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put(m % 10, 32, 4); put(m // 10, 40, 3); put(h % 10, 48, 4); put(h // 10, 56, 2)
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bits[64:80] = [0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1]
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return bits
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def write(path, start=(1, 2, 3, 4), seconds=2, rate=48000, fps=30, amp=0.5):
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h, m, s, f = start
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per_bit = rate / (fps * 80.0)
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level, t, samples = 1, 0.0, []
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for _ in range(seconds * fps):
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for b in frame_bits(h, m, s, f):
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level = -level # a transition at every bit start
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half = per_bit / 2
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for k in range(2):
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if k == 1 and b:
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level = -level # and one in the middle of a 1
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t += half
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while len(samples) < int(round(t)):
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samples.append(level * amp)
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f += 1
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if f == fps:
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f, s = 0, s + 1
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w = wave.open(path, "wb")
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w.setnchannels(1); w.setsampwidth(2); w.setframerate(rate)
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w.writeframes(b"".join(struct.pack("<h", int(x * 32767)) for x in samples))
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w.close()
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if __name__ == "__main__":
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write(sys.argv[1])
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