kopia lustrzana https://github.com/dnet/pySSTV
137 wiersze
4.3 KiB
Python
137 wiersze
4.3 KiB
Python
#!/usr/bin/env python
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from __future__ import division, with_statement
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from math import sin, pi
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from random import random
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from contextlib import closing
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from itertools import cycle, chain
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from array import array
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import wave
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FREQ_VIS_BIT1 = 1100
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FREQ_SYNC = 1200
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FREQ_VIS_BIT0 = 1300
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FREQ_BLACK = 1500
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FREQ_VIS_START = 1900
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FREQ_WHITE = 2300
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FREQ_RANGE = FREQ_WHITE - FREQ_BLACK
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FREQ_FSKID_BIT1 = 1900
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FREQ_FSKID_BIT0 = 2100
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MSEC_VIS_START = 300
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MSEC_VIS_SYNC = 10
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MSEC_VIS_BIT = 30
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MSEC_FSKID_BIT = 22
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class SSTV(object):
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def __init__(self, image, samples_per_sec, bits):
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self.image = image
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self.samples_per_sec = samples_per_sec
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self.bits = bits
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self.vox_enabled = False
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self.fskid_payload = ''
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self.nchannels = 1
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self.on_init()
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def on_init(self):
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pass
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BITS_TO_STRUCT = {8: 'b', 16: 'h'}
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def write_wav(self, filename):
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"""writes the whole image to a Microsoft WAV file"""
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fmt = self.BITS_TO_STRUCT[self.bits]
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data = array(fmt, self.gen_samples())
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if self.nchannels != 1:
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data = array(fmt, chain.from_iterable(
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zip(*([data] * self.nchannels))))
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with closing(wave.open(filename, 'wb')) as wav:
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wav.setnchannels(self.nchannels)
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wav.setsampwidth(self.bits // 8)
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wav.setframerate(self.samples_per_sec)
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wav.writeframes(data)
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def gen_samples(self):
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"""generates discrete samples from gen_values()
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performs quantization according to
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the bits per sample value given during construction
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"""
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max_value = 2 ** self.bits
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alias = 1 / max_value
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amp = max_value // 2
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lowest = -amp
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highest = amp - 1
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alias_cycle = cycle((alias * (random() - 0.5) for _ in range(1024)))
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for value, alias_item in zip(self.gen_values(), alias_cycle):
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sample = int(value * amp + alias_item)
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yield (lowest if sample <= lowest else
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sample if sample <= highest else highest)
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def gen_values(self):
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"""generates samples between -1 and +1 from gen_freq_bits()
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performs sampling according to
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the samples per second value given during construction
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"""
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spms = self.samples_per_sec / 1000
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offset = 0
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samples = 0
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factor = 2 * pi / self.samples_per_sec
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sample = 0
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for freq, msec in self.gen_freq_bits():
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samples += spms * msec
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tx = int(samples)
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freq_factor = freq * factor
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for sample in range(tx):
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yield sin(sample * freq_factor + offset)
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offset += (sample + 1) * freq_factor
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samples -= tx
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def gen_freq_bits(self):
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"""generates tuples (freq, msec) that describe a sine wave segment
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frequency "freq" in Hz and duration "msec" in ms
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"""
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if self.vox_enabled:
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for freq in (1900, 1500, 1900, 1500, 2300, 1500, 2300, 1500):
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yield freq, 100
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yield FREQ_VIS_START, MSEC_VIS_START
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yield FREQ_SYNC, MSEC_VIS_SYNC
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yield FREQ_VIS_START, MSEC_VIS_START
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yield FREQ_SYNC, MSEC_VIS_BIT # start bit
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vis = self.VIS_CODE
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num_ones = 0
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for _ in range(7):
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bit = vis & 1
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vis >>= 1
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num_ones += bit
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bit_freq = FREQ_VIS_BIT1 if bit == 1 else FREQ_VIS_BIT0
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yield bit_freq, MSEC_VIS_BIT
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parity_freq = FREQ_VIS_BIT1 if num_ones % 2 == 1 else FREQ_VIS_BIT0
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yield parity_freq, MSEC_VIS_BIT
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yield FREQ_SYNC, MSEC_VIS_BIT # stop bit
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yield from self.gen_image_tuples()
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for fskid_byte in map(ord, self.fskid_payload):
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for _ in range(6):
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bit = fskid_byte & 1
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fskid_byte >>= 1
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bit_freq = FREQ_FSKID_BIT1 if bit == 1 else FREQ_FSKID_BIT0
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yield bit_freq, MSEC_FSKID_BIT
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def gen_image_tuples(self):
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return []
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def add_fskid_text(self, text):
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self.fskid_payload += '\x20\x2a{0}\x01'.format(
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''.join(chr(ord(c) - 0x20) for c in text))
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def horizontal_sync(self):
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yield FREQ_SYNC, self.SYNC
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def byte_to_freq(value):
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return FREQ_BLACK + FREQ_RANGE * value / 255
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