tcview/tools.py

#!/usr/bin/env python3
from timecode import Timecode

def bitstring_to_bytes(s, bytecount=1, byteorder='big'):
	return int(s, 2).to_bytes(bytecount, byteorder)

# binary big-endian
def bbe(n, bits=8):
	# terminal condition
	retval = ''
	if n == 0:
		retval = '0'
	else:
		retval = bbe(n//2, None) + str(n%2)
	if bits is None:
		return retval
	else:
		return (('0'*bits) + retval)[-bits:]
	

# binary, little-endian
def ble(n, bits=8):
	# terminal condition
	retval = ''
	if n == 0:
		retval = '0'
	else:
		retval = str(n%2) + ble(n//2, None)
	if bits is None:
		return retval
	else:
		return (retval + ('0'*bits))[0:bits]

def cint(n, bytecount=2):
	return int(n).to_bytes(bytecount, byteorder='little')

def units_tens(n):
	return n % 10, int(n/10)

##
## LTC functions
##
# GENERATE BINARY-CODED DATA FOR LTC
# ACCORDING TO https://en.wikipedia.org/wiki/Linear_timecode
# everything is encoded little endian
# so to encode the number 3 with four bits, we have 1100
def ltc_encode(timecode, as_string=False):
	LTC = ''
	HLP = ''
	hrs, mins, secs, frs = timecode.frames_to_tc(timecode.frames)
	frame_units, frame_tens = units_tens(frs)
	secs_units, secs_tens = units_tens(secs)
	mins_units, mins_tens = units_tens(mins)
	hrs_units, hrs_tens = units_tens(hrs)
	
	#frames units / user bits field 1 / frames tens
	LTC += ble(frame_units,4) + '0000' + ble(frame_tens,2)
	HLP += '---{u}____-{t}'.format(u=frame_units, t=frame_tens)
	
	#drop frame / color frame / user bits field 2
	LTC += '00'+'0000'
	HLP += '__'+'____'
	
	#secs units / user bits field 3 / secs tens
	LTC += ble(secs_units,4) + '0000' + ble(secs_tens,3)
	HLP += '---{u}____--{t}'.format(u=secs_units, t=secs_tens)

	# bit 27 flag / user bits field 4
	LTC += '0' + '0000'
	HLP += '_' + '____'

	#mins units / user bits field 5 / mins tens
	LTC += ble(mins_units,4) + '0000' + ble(mins_tens,3)
	HLP += '---{u}____--{t}'.format(u=mins_units, t=mins_tens)

	# bit 43 flag / user bits field 6
	LTC += '0' + '0000'
	HLP += '_' + '____'

	#hrs units / user bits field 7 / hrs tens
	LTC += ble(hrs_units,4) + '0000' + ble(hrs_tens,2)
	HLP += '---{u}____--{t}'.format(u=hrs_units, t=hrs_tens)

	# bit 58 clock flag / bit 59 flag / user bits field 8
	LTC += '0' + '0' + '0000'
	HLP += '_' + '_' + '____'

	# sync word
	LTC += '0011111111111101'
	HLP += '################'
	if as_string:
		return LTC
	else:
		return bitstring_to_bytes(LTC, bytecount=10)


##
## MTC functions
##
def mtc_encode(timecode, as_string=False):
	# MIDI bytes are little-endian
	# Byte 0
	#   0rrhhhhh: Rate (0–3) and hour (0–23).
	#   rr = 000: 24 frames/s
	#   rr = 001: 25 frames/s
	#   rr = 010: 29.97 frames/s (SMPTE drop-frame timecode)
	#   rr = 011: 30 frames/s
	# Byte 1
	#   00mmmmmm: Minute (0–59)
	# Byte 2
	#   00ssssss: Second (0–59)
	# Byte 3
	#   000fffff: Frame (0–29, or less at lower frame rates)
	hrs, mins, secs, frs = timecode.frames_to_tc(timecode.frames)
	framerate = timecode.framerate
	rateflags = {
		'24':    0,
		'25':    1,
		'29.97': 2,
		'30':    3
	}
	rateflag = rateflags[framerate] * 32  # multiply by 32, because the rate flag starts at bit 6

	# print('{:8} {:8} {:8} {:8}'.format(hrs, mins, secs, frs))
	if as_string:
		b0 = bbe(rateflag + hrs, 8)
		b1 = bbe(mins)
		b2 = bbe(secs)
		b3 = bbe(frs)
		# print('{:8} {:8} {:8} {:8}'.format(b0, b1, b2, b3))
		return b0+b1+b2+b3
	else:
		b = bytearray([rateflag + hrs, mins, secs, frs])
		# debug_string = '    0x{:02}     0x{:02}     0x{:02}     0x{:02}'
		# debug_array  = [ord(b[0]), ord(b[1]), ord(b[2]), ord(b[3])]
		# print(debug_string.format(debug_array))
		return b

# convert a bytearray back to timecode
def mtc_decode(mtc_bytes):
	rhh, mins, secs, frs = mtc_bytes
	rateflag = rhh >> 5
	hrs      = rhh & 31
	fps = ['24','25','29.97','30'][rateflag]
	total_frames = int(frs + float(fps) * (secs + mins * 60 + hrs * 60 * 60))
	return Timecode(fps, frames=total_frames)

def mtc_full_frame(timecode):
	# if sending this to a MIDI device, remember that MIDI is generally little endian
	# but the full frame timecode bytes are big endian
	mtc_bytes = mtc_encode(timecode)
	# mtc full frame has a special header and ignores the rate flag
	return bytearray([0xf0, 0x7f, 0x7f, 0x01, 0x01]) + mtc_bytes + bytearray([0xf7])

def mtc_decode_full_frame(full_frame_bytes):
	mtc_bytes = full_frame_bytes[5:-1]
	return mtc_decode(mtc_bytes)

def mtc_quarter_frame(timecode, piece=0):
	# there are 8 different mtc_quarter frame pieces
	# see https://en.wikipedia.org/wiki/MIDI_timecode
	# and https://web.archive.org/web/20120212181214/http://home.roadrunner.com/~jgglatt/tech/mtc.htm
	# these are little-endian bytes
	# piece 0 : 0xF1 0000 ffff frame
	mtc_bytes = mtc_encode(timecode)
	this_byte = mtc_bytes[3 - piece//2]   #the order of pieces is the reverse of the mtc_encode
	if piece % 2 == 0:
		# even pieces get the low nibble
		nibble = this_byte & 15
	else:
		# odd pieces get the high nibble
		nibble = this_byte >> 4
	return bytearray([0xf1, piece * 16 + nibble])

def mtc_decode_quarter_frames(frame_pieces):
	mtc_bytes = bytearray(4)
	if len(frame_pieces) < 8:
		return None
	for piece in range(8):
		mtc_index = 3 - piece//2    # quarter frame pieces are in reverse order of mtc_encode
		this_frame = frame_pieces[piece]
		if this_frame is bytearray or this_frame is list:
			this_frame = this_frame[1]
		data = this_frame & 15      # ignore the frame_piece marker bits
		if piece % 2 == 0:
			# 'even' pieces came from the low nibble
			# and the first piece is 0, so it's even
			mtc_bytes[mtc_index] += data
		else:
			# 'odd' pieces came from the high nibble
			mtc_bytes[mtc_index] += data * 16
	return mtc_decode(mtc_bytes)