class FlacDecoder:
CHANNEL_COUNT = [1, 2, 3, 4, 5, 6, 7, 8, 2, 2, 2,
None, None, None, None, None]
(SUBFRAME_CONSTANT,
SUBFRAME_VERBATIM,
SUBFRAME_FIXED,
SUBFRAME_LPC) = range(4)
def __init__(self, filename, channel_mask):
self.reader = BitstreamReader(open(filename, "rb"), 0)
if (self.reader.read_bytes(4) != 'fLaC'):
raise ValueError("invalid FLAC file")
self.current_md5sum = md5()
#locate the STREAMINFO,
#which is sometimes needed to handle non-subset streams
for (block_id,
block_size,
block_reader) in self.metadata_blocks(self.reader):
if (block_id == 0):
#read STREAMINFO
self.minimum_block_size = block_reader.read(16)
self.maximum_block_size = block_reader.read(16)
self.minimum_frame_size = block_reader.read(24)
self.maximum_frame_size = block_reader.read(24)
self.sample_rate = block_reader.read(20)
self.channels = block_reader.read(3) + 1
self.channel_mask = channel_mask
self.bits_per_sample = block_reader.read(5) + 1
self.total_frames = block_reader.read64(36)
self.md5sum = block_reader.read_bytes(16)
#these are frame header lookup tables
#which vary slightly depending on STREAMINFO's values
self.BLOCK_SIZE = [self.maximum_block_size,
192, 576, 1152,
2304, 4608, None, None,
256, 512, 1024, 2048,
4096, 8192, 16384, 32768]
self.SAMPLE_RATE = [self.sample_rate,
88200, 176400, 192000,
8000, 16000, 22050, 24000,
32000, 44100, 48000, 96000,
None, None, None, None]
self.BITS_PER_SAMPLE = [self.bits_per_sample,
8, 12, None, 16, 20, 24, None]
def metadata_blocks(self, reader):
"""yields a (block_id, block_size, block_reader) tuple
per metadata block where block_reader is a BitstreamReader substream"""
(last_block, block_id, block_size) = self.reader.parse("1u 7u 24u")
while (last_block == 0):
yield (block_id, block_size, self.reader.substream(block_size))
(last_block, block_id, block_size) = self.reader.parse("1u 7u 24u")
else:
yield (block_id, block_size, self.reader.substream(block_size))
def read(self, pcm_frames):
#if the stream is exhausted,
#verify its MD5 sum and return an empty pcm.FrameList object
if (self.total_frames < 1):
if (self.md5sum == self.current_md5sum.digest()):
return from_list([], self.channels, self.bits_per_sample, True)
else:
raise ValueError("MD5 checksum mismatch")
crc16 = CRC16()
self.reader.add_callback(crc16.update)
#fetch the decoding parameters from the frame header
(block_size,
channel_assignment,
bits_per_sample) = self.read_frame_header()
channel_count = self.CHANNEL_COUNT[channel_assignment]
if (channel_count is None):
raise ValueError("invalid channel assignment")
#channel data will be a list of signed sample lists, one per channel
#such as [[1, 2, 3, ...], [4, 5, 6, ...]] for a 2 channel stream
channel_data = []
for channel_number in xrange(channel_count):
if ((channel_assignment == 0x8) and (channel_number == 1)):
#for left-difference assignment
#the difference channel has 1 additional bit
channel_data.append(self.read_subframe(block_size,
bits_per_sample + 1))
elif ((channel_assignment == 0x9) and (channel_number == 0)):
#for difference-right assignment
#the difference channel has 1 additional bit
channel_data.append(self.read_subframe(block_size,
bits_per_sample + 1))
elif ((channel_assignment == 0xA) and (channel_number == 1)):
#for mid-side assignment
#the side channel has 1 additional bit
channel_data.append(self.read_subframe(block_size,
bits_per_sample + 1))
else:
#otherwise, use the frame's bits-per-sample value
channel_data.append(self.read_subframe(block_size,
bits_per_sample))
#one all the subframes have been decoded,
#reconstruct them depending on the channel assignment
if (channel_assignment == 0x8):
#left-difference
samples = []
for (left, difference) in zip(*channel_data):
samples.append(left)
samples.append(left - difference)
elif (channel_assignment == 0x9):
#difference-right
samples = []
for (difference, right) in zip(*channel_data):
samples.append(difference + right)
samples.append(right)
elif (channel_assignment == 0xA):
#mid-side
samples = []
for (mid, side) in zip(*channel_data):
samples.append((((mid * 2) + (side % 2)) + side) / 2)
samples.append((((mid * 2) + (side % 2)) - side) / 2)
else:
#independent
samples = [0] * block_size * channel_count
for (i, channel) in enumerate(channel_data):
samples[i::channel_count] = channel
self.reader.byte_align()
#read and verify the frame's trailing CRC-16 footer
self.reader.read(16)
self.reader.pop_callback()
if (int(crc16) != 0):
raise ValueError("CRC16 mismatch in frame footer")
#deduct the amount of PCM frames from the remaining amount
self.total_frames -= block_size
#build a pcm.FrameList object from the combined samples
framelist = from_list(samples, channel_count, bits_per_sample, True)
#update the running MD5 sum calculation with the frame's data
self.current_md5sum.update(framelist.to_bytes(0, 1))
#and finally return the frame data
return framelist
def read_frame_header(self):
crc8 = CRC8()
self.reader.add_callback(crc8.update)
#read the 32-bit FLAC frame header
sync_code = self.reader.read(14)
if (sync_code != 0x3FFE):
raise ValueError("invalid sync code")
self.reader.skip(1)
blocking_strategy = self.reader.read(1)
block_size_bits = self.reader.read(4)
sample_rate_bits = self.reader.read(4)
channel_assignment = self.reader.read(4)
bits_per_sample_bits = self.reader.read(3)
self.reader.skip(1)
#the frame number is a UTF-8 encoded value
#which takes a variable number of whole bytes
frame_number = self.read_utf8()
#unpack the 4 bit block size field
#which is the total PCM frames in the FLAC frame
#and may require up to 16 more bits if the frame is usually-sized
#(which typically happens at the end of the stream)
if (block_size_bits == 0x6):
block_size = self.reader.read(8) + 1
elif (block_size_bits == 0x7):
block_size = self.reader.read(16) + 1
else:
block_size = self.BLOCK_SIZE[block_size_bits]
#unpack the 4 bit sample rate field
#which is used for playback, but not needed for decoding
#and may require up to 16 more bits
#if the stream has a particularly unusual sample rate
if (sample_rate_bits == 0xC):
sample_rate = self.reader.read(8) * 1000
elif (sample_rate_bits == 0xD):
sample_rate = self.reader.read(16)
elif (sample_rate_bits == 0xE):
sample_rate = self.reader.read(16) * 10
elif (sample_rate_bits == 0xF):
raise ValueError("invalid sample rate")
else:
sample_rate = self.SAMPLE_RATE[sample_rate_bits]
#unpack the 3 bit bits-per-sample field
#this never requires additional bits
if ((bits_per_sample_bits == 0x3) or (bits_per_sample_bits == 0x7)):
raise ValueError("invalid bits per sample")
else:
bits_per_sample = self.BITS_PER_SAMPLE[bits_per_sample_bits]
#read and verify frame's CRC-8 value
self.reader.read(8)
self.reader.pop_callback()
if (int(crc8) != 0):
raise ValueError("CRC8 mismatch in frame header")
return (block_size, channel_assignment, bits_per_sample)
def read_subframe_header(self):
"""returns a tuple of (subframe_type, subframe_order, wasted_bps)"""
self.reader.skip(1)
subframe_type = self.reader.read(6)
if (self.reader.read(1) == 1):
wasted_bps = self.reader.unary(1) + 1
else:
wasted_bps = 0
#extract "order" value from 6 bit subframe type, if necessary
if (subframe_type == 0):
return (self.SUBFRAME_CONSTANT, None, wasted_bps)
elif (subframe_type == 1):
return (self.SUBFRAME_VERBATIM, None, wasted_bps)
elif ((subframe_type & 0x38) == 0x08):
return (self.SUBFRAME_FIXED, subframe_type & 0x07, wasted_bps)
elif ((subframe_type & 0x20) == 0x20):
return (self.SUBFRAME_LPC, (subframe_type & 0x1F) + 1, wasted_bps)
else:
raise ValueError("invalid subframe type")
def read_subframe(self, block_size, bits_per_sample):
(subframe_type,
subframe_order,
wasted_bps) = self.read_subframe_header()
#read a list of signed sample values
#depending on the subframe type, block size,
#adjusted bits per sample and optional subframe order
if (subframe_type == self.SUBFRAME_CONSTANT):
subframe_samples = self.read_constant_subframe(
block_size, bits_per_sample - wasted_bps)
elif (subframe_type == self.SUBFRAME_VERBATIM):
subframe_samples = self.read_verbatim_subframe(
block_size, bits_per_sample - wasted_bps)
elif (subframe_type == self.SUBFRAME_FIXED):
subframe_samples = self.read_fixed_subframe(
block_size, bits_per_sample - wasted_bps, subframe_order)
else:
subframe_samples = self.read_lpc_subframe(
block_size, bits_per_sample - wasted_bps, subframe_order)
#account for wasted bits-per-sample, if necessary
if (wasted_bps):
return [sample << wasted_bps for sample in subframe_samples]
else:
return subframe_samples
def read_constant_subframe(self, block_size, bits_per_sample):
sample = self.reader.read_signed(bits_per_sample)
return [sample] * block_size
def read_verbatim_subframe(self, block_size, bits_per_sample):
return [self.reader.read_signed(bits_per_sample)
for x in xrange(block_size)]
def read_fixed_subframe(self, block_size, bits_per_sample, order):
#"order" number of warm-up samples
samples = [self.reader.read_signed(bits_per_sample)
for i in xrange(order)]
#"block_size" - "order" number of residual values
residuals = self.read_residual(block_size, order)
#which are applied to the warm-up samples
#depending on the FIXED subframe order
#and results in "block_size" number of total samples
if (order == 0):
return residuals
elif (order == 1):
for residual in residuals:
samples.append(
samples[-1] +
residual)
return samples
elif (order == 2):
for residual in residuals:
samples.append(
(2 * samples[-1]) -
samples[-2] +
residual)
return samples
elif (order == 3):
for residual in residuals:
samples.append(
(3 * samples[-1]) -
(3 * samples[-2]) +
samples[-3] +
residual)
return samples
elif (order == 4):
for residual in residuals:
samples.append(
(4 * samples[-1]) -
(6 * samples[-2]) +
(4 * samples[-3]) -
samples[-4] +
residual)
return samples
else:
raise ValueError("unsupported FIXED subframe order")
def read_lpc_subframe(self, block_size, bits_per_sample, order):
#"order" number of warm-up samples
samples = [self.reader.read_signed(bits_per_sample)
for i in xrange(order)]
#the size of each QLP coefficient, in bits
qlp_precision = self.reader.read(4)
#the amount of right shift to apply
#during LPC calculation
#(though this is a signed value, negative shifts are noops
# in the reference FLAC decoder)
qlp_shift_needed = max(self.reader.read_signed(5), 0)
#"order" number of signed QLP coefficients
qlp_coeffs = [self.reader.read_signed(qlp_precision + 1)
for i in xrange(order)]
#QLP coefficients are applied in reverse order
qlp_coeffs.reverse()
#"block_size" - "order" number of residual values
residuals = self.read_residual(block_size, order)
#which are applied to the running LPC calculation
for residual in residuals:
samples.append((sum([coeff * sample for (coeff, sample) in
zip(qlp_coeffs, samples[-order:])]) >>
qlp_shift_needed) + residual)
return samples
def read_residual(self, block_size, order):
residuals = []
coding_method = self.reader.read(2)
partition_order = self.reader.read(4)
#each parititon contains block_size / 2 ** partition_order
#number of residuals
for partition_number in xrange(2 ** partition_order):
if (partition_number == 0):
#except for the first partition
#which contains "order" less than the rest
residuals.extend(
self.read_residual_partition(
coding_method,
(block_size / 2 ** partition_order) - order))
else:
residuals.extend(
self.read_residual_partition(
coding_method,
block_size / 2 ** partition_order))
return residuals
def read_residual_partition(self, coding_method, residual_count):
if (coding_method == 0):
#the Rice parameters determines the number of
#least-significant bits to read for each residual
rice_parameter = self.reader.read(4)
if (rice_parameter == 0xF):
escape_code = self.reader.read(5)
return [self.reader.read_signed(escape_code)
for i in xrange(residual_count)]
elif (coding_method == 1):
#24 bps streams may use a 5-bit Rice parameter
#for better compression
rice_parameter = self.reader.read(5)
if (rice_parameter == 0x1F):
escape_code = self.reader.read(5)
return [self.reader.read_signed(escape_code)
for i in xrange(residual_count)]
else:
raise ValueError("invalid Rice coding parameter")
#a list of signed residual values
partition_residuals = []
for i in xrange(residual_count):
msb = self.reader.unary(1) # most-significant bits
lsb = self.reader.read(rice_parameter) # least-significant bits
value = (msb << rice_parameter) | lsb # combined into a value
if (value & 1): # whose least-significant bit is the sign value
partition_residuals.append(-(value >> 1) - 1)
else:
partition_residuals.append(value >> 1)
return partition_residuals
def read_utf8(self):
total_bytes = self.reader.unary(0)
value = self.reader.read(7 - total_bytes)
while (total_bytes > 1):
value = ((value << 6) | self.reader.parse("2p 6u")[0])
total_bytes -= 1
return value
def close(self):
self.reader.close()
class TTADecoder:
def __init__(self, filename):
self.reader = BitstreamReader(open(filename, "rb"), True)
crc = CRC32()
self.reader.add_callback(crc.update)
#read the header
(signature,
format_,
self.channels,
self.bits_per_sample,
self.sample_rate,
self.total_pcm_frames) = self.reader.parse(
"4b 16u 16u 16u 32u 32u")
self.reader.pop_callback()
header_crc = self.reader.read(32)
if (int(crc) != header_crc):
raise ValueError(
"CRC32 mismatch in header (0x%8.8X != 0x%8.8X)" %
(header_crc, int(crc)))
self.channel_mask = {1:0x4, 2:0x3}.get(self.channels, 0)
total_tta_frames = div_ceil(self.total_pcm_frames * 245,
self.sample_rate * 256)
self.pcm_frames_per_tta_frame = (self.sample_rate * 256) / 245
#read the seektable
crc = CRC32()
self.reader.add_callback(crc.update)
self.frame_sizes = [self.reader.read(32) for i in
xrange(total_tta_frames)]
self.reader.pop_callback()
seektable_crc = self.reader.read(32)
if (int(crc) != seektable_crc):
raise ValueError(
"CRC32 mismatch in seektable (0x%8.8X != 0x%8.8X)" %
(header_crc, int(crc)))
self.current_tta_frame = 0
def read(self, pcm_frames):
if (self.total_pcm_frames == 0):
return FrameList("",
self.channels,
self.bits_per_sample,
True,
True)
pcm_frames = min(self.pcm_frames_per_tta_frame, self.total_pcm_frames)
frame_reader = self.reader.substream(
self.frame_sizes[self.current_tta_frame])
crc = CRC32()
frame_reader.add_callback(crc.update)
self.total_pcm_frames -= pcm_frames
self.current_tta_frame += 1
#setup Rice parameters for each channel
k0 = [10] * self.channels
k1 = [10] * self.channels
sum0 = [2 ** 14] * self.channels
sum1 = [2 ** 14] * self.channels
#list of unfiltered output for each channel
unfiltered = [[] for i in xrange(self.channels)]
for f in xrange(pcm_frames):
correlated = []
for (c, ch_output) in enumerate(unfiltered):
#read most-significant bits
MSB = frame_reader.unary(0)
if (MSB == 0):
#read least-significant bits
unsigned = frame_reader.read(k0[c])
else:
#read least-significant bits
LSB = frame_reader.read(k1[c])
unshifted = ((MSB - 1) << k1[c]) + LSB
unsigned = unshifted + (1 << k0[c])
#adjust sum1 and k1
sum1[c] += (unshifted - (sum1[c] >> 4))
if (sum1[c] < (2 ** (k1[c] + 4))):
k1[c] = max(k1[c] - 1, 0)
elif (sum1[c] > (2 ** (k1[c] + 5))):
k1[c] += 1
#adjust sum0 and k0
sum0[c] += (unsigned - (sum0[c] >> 4))
if (sum0[c] < (2 ** (k0[c] + 4))):
k0[c] = max(k0[c] - 1, 0)
elif (sum0[c] > (2 ** (k0[c] + 5))):
k0[c] += 1
#apply sign bit
if ((unsigned % 2) == 1):
#positive
ch_output.append((unsigned + 1) / 2)
else:
#negative
ch_output.append(-(unsigned / 2))
#check frame's trailing CRC32 now that reading is finished
frame_reader.byte_align()
frame_reader.pop_callback()
frame_crc = frame_reader.read(32)
if (int(crc) != frame_crc):
raise ValueError("CRC32 mismatch in frame (0x%8.8X != 0x%8.8X)" %
(frame_crc, int(crc)))
#run hybrid filter on each channel
filtered = []
for unfiltered_ch in unfiltered:
filtered.append(
tta_filter(self.bits_per_sample, unfiltered_ch))
#run fixed order prediction on each channel
predicted = []
for filtered_ch in filtered:
predicted.append(
fixed_predictor(self.bits_per_sample, filtered_ch))
if (self.channels == 1):
#send channel as-is
return from_list(predicted[0],
1,
self.bits_per_sample,
True)
else:
#decorrelate channels
decorrelated = decorrelate(predicted)
#return all channels as single FrameList
return from_channels([from_list(decorrelated_ch,
1,
self.bits_per_sample,
True)
for decorrelated_ch in decorrelated])
def close(self):
#FIXME
pass
class TTADecoder(object):
def __init__(self, filename):
self.reader = BitstreamReader(open(filename, "rb"), True)
crc = CRC32()
self.reader.add_callback(crc.update)
# read the header
(signature, format_, self.channels, self.bits_per_sample,
self.sample_rate,
self.total_pcm_frames) = self.reader.parse("4b 16u 16u 16u 32u 32u")
self.reader.pop_callback()
header_crc = self.reader.read(32)
if (int(crc) != header_crc):
raise ValueError("CRC32 mismatch in header (0x%8.8X != 0x%8.8X)" %
(header_crc, int(crc)))
self.channel_mask = {1: 0x4, 2: 0x3}.get(self.channels, 0)
total_tta_frames = div_ceil(self.total_pcm_frames * 245,
self.sample_rate * 256)
self.pcm_frames_per_tta_frame = (self.sample_rate * 256) // 245
# read the seektable
crc = CRC32()
self.reader.add_callback(crc.update)
self.frame_sizes = [
self.reader.read(32) for i in range(total_tta_frames)
]
self.reader.pop_callback()
seektable_crc = self.reader.read(32)
if (int(crc) != seektable_crc):
raise ValueError(
"CRC32 mismatch in seektable (0x%8.8X != 0x%8.8X)" %
(header_crc, int(crc)))
self.current_tta_frame = 0
def read(self, pcm_frames):
if (self.total_pcm_frames == 0):
return FrameList("", self.channels, self.bits_per_sample, True,
True)
pcm_frames = min(self.pcm_frames_per_tta_frame, self.total_pcm_frames)
frame_reader = self.reader.substream(
self.frame_sizes[self.current_tta_frame])
crc = CRC32()
frame_reader.add_callback(crc.update)
self.total_pcm_frames -= pcm_frames
self.current_tta_frame += 1
# setup Rice parameters for each channel
k0 = [10] * self.channels
k1 = [10] * self.channels
sum0 = [2**14] * self.channels
sum1 = [2**14] * self.channels
# list of unfiltered output for each channel
unfiltered = [[] for i in range(self.channels)]
for f in range(pcm_frames):
correlated = []
for (c, ch_output) in enumerate(unfiltered):
# read most-significant bits
MSB = frame_reader.unary(0)
if (MSB == 0):
# read least-significant bits
unsigned = frame_reader.read(k0[c])
else:
# read least-significant bits
LSB = frame_reader.read(k1[c])
unshifted = ((MSB - 1) << k1[c]) + LSB
unsigned = unshifted + (1 << k0[c])
# adjust sum1 and k1
sum1[c] += (unshifted - (sum1[c] >> 4))
if (sum1[c] < (2**(k1[c] + 4))):
k1[c] = max(k1[c] - 1, 0)
elif (sum1[c] > (2**(k1[c] + 5))):
k1[c] += 1
# adjust sum0 and k0
sum0[c] += (unsigned - (sum0[c] >> 4))
if (sum0[c] < (2**(k0[c] + 4))):
k0[c] = max(k0[c] - 1, 0)
elif (sum0[c] > (2**(k0[c] + 5))):
k0[c] += 1
# apply sign bit
if ((unsigned % 2) == 1):
# positive
ch_output.append((unsigned + 1) // 2)
else:
# negative
ch_output.append(-(unsigned // 2))
# check frame's trailing CRC32 now that reading is finished
frame_reader.byte_align()
frame_reader.pop_callback()
frame_crc = frame_reader.read(32)
if (int(crc) != frame_crc):
raise ValueError("CRC32 mismatch in frame (0x%8.8X != 0x%8.8X)" %
(frame_crc, int(crc)))
# run hybrid filter on each channel
filtered = []
for unfiltered_ch in unfiltered:
filtered.append(tta_filter(self.bits_per_sample, unfiltered_ch))
# run fixed order prediction on each channel
predicted = []
for filtered_ch in filtered:
predicted.append(fixed_predictor(self.bits_per_sample,
filtered_ch))
if (self.channels == 1):
# send channel as-is
return from_list(predicted[0], 1, self.bits_per_sample, True)
else:
# decorrelate channels
decorrelated = decorrelate(predicted)
# return all channels as single FrameList
return from_channels([
from_list(decorrelated_ch, 1, self.bits_per_sample, True)
for decorrelated_ch in decorrelated
])
def close(self):
# FIXME
pass
class FlacDecoder(object):
CHANNEL_COUNT = [
1, 2, 3, 4, 5, 6, 7, 8, 2, 2, 2, None, None, None, None, None
]
(SUBFRAME_CONSTANT, SUBFRAME_VERBATIM, SUBFRAME_FIXED,
SUBFRAME_LPC) = range(4)
def __init__(self, filename, channel_mask):
self.reader = BitstreamReader(open(filename, "rb"), False)
if (self.reader.read_bytes(4) != b'fLaC'):
raise ValueError("invalid FLAC file")
self.current_md5sum = md5()
# locate the STREAMINFO,
# which is sometimes needed to handle non-subset streams
for (block_id, block_size,
block_reader) in self.metadata_blocks(self.reader):
if (block_id == 0):
# read STREAMINFO
self.minimum_block_size = block_reader.read(16)
self.maximum_block_size = block_reader.read(16)
self.minimum_frame_size = block_reader.read(24)
self.maximum_frame_size = block_reader.read(24)
self.sample_rate = block_reader.read(20)
self.channels = block_reader.read(3) + 1
self.channel_mask = channel_mask
self.bits_per_sample = block_reader.read(5) + 1
self.total_frames = block_reader.read(36)
self.md5sum = block_reader.read_bytes(16)
# these are frame header lookup tables
# which vary slightly depending on STREAMINFO's values
self.BLOCK_SIZE = [
self.maximum_block_size, 192, 576, 1152, 2304, 4608, None,
None, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768
]
self.SAMPLE_RATE = [
self.sample_rate, 88200, 176400, 192000, 8000, 16000,
22050, 24000, 32000, 44100, 48000, 96000, None, None, None,
None
]
self.BITS_PER_SAMPLE = [
self.bits_per_sample, 8, 12, None, 16, 20, 24, None
]
def metadata_blocks(self, reader):
"""yields a (block_id, block_size, block_reader) tuple
per metadata block where block_reader is a BitstreamReader substream"""
(last_block, block_id, block_size) = self.reader.parse("1u 7u 24u")
while (last_block == 0):
yield (block_id, block_size, self.reader.substream(block_size))
(last_block, block_id, block_size) = self.reader.parse("1u 7u 24u")
else:
yield (block_id, block_size, self.reader.substream(block_size))
def read(self, pcm_frames):
# if the stream is exhausted,
# verify its MD5 sum and return an empty pcm.FrameList object
if (self.total_frames < 1):
if (self.md5sum == self.current_md5sum.digest()):
return empty_framelist(self.channels, self.bits_per_sample)
else:
raise ValueError("MD5 checksum mismatch")
crc16 = CRC16()
self.reader.add_callback(crc16.update)
# fetch the decoding parameters from the frame header
(block_size, channel_assignment,
bits_per_sample) = self.read_frame_header()
channel_count = self.CHANNEL_COUNT[channel_assignment]
if (channel_count is None):
raise ValueError("invalid channel assignment")
# channel data will be a list of signed sample lists, one per channel
# such as [[1, 2, 3, ...], [4, 5, 6, ...]] for a 2 channel stream
channel_data = []
for channel_number in range(channel_count):
if ((channel_assignment == 0x8) and (channel_number == 1)):
# for left-difference assignment
# the difference channel has 1 additional bit
channel_data.append(
self.read_subframe(block_size, bits_per_sample + 1))
elif ((channel_assignment == 0x9) and (channel_number == 0)):
# for difference-right assignment
# the difference channel has 1 additional bit
channel_data.append(
self.read_subframe(block_size, bits_per_sample + 1))
elif ((channel_assignment == 0xA) and (channel_number == 1)):
# for average-difference assignment
# the difference channel has 1 additional bit
channel_data.append(
self.read_subframe(block_size, bits_per_sample + 1))
else:
# otherwise, use the frame's bits-per-sample value
channel_data.append(
self.read_subframe(block_size, bits_per_sample))
# one all the subframes have been decoded,
# reconstruct them depending on the channel assignment
if (channel_assignment == 0x8):
# left-difference
samples = []
for (left, difference) in zip(*channel_data):
samples.append(left)
samples.append(left - difference)
elif (channel_assignment == 0x9):
# difference-right
samples = []
for (difference, right) in zip(*channel_data):
samples.append(difference + right)
samples.append(right)
elif (channel_assignment == 0xA):
# mid-side
samples = []
for (mid, side) in zip(*channel_data):
samples.append((((mid * 2) + (side % 2)) + side) // 2)
samples.append((((mid * 2) + (side % 2)) - side) // 2)
else:
# independent
samples = [0] * block_size * channel_count
for (i, channel) in enumerate(channel_data):
samples[i::channel_count] = channel
self.reader.byte_align()
# read and verify the frame's trailing CRC-16 footer
self.reader.read(16)
self.reader.pop_callback()
if (int(crc16) != 0):
raise ValueError("CRC16 mismatch in frame footer")
# deduct the amount of PCM frames from the remaining amount
self.total_frames -= block_size
# build a pcm.FrameList object from the combined samples
framelist = from_list(samples, channel_count, bits_per_sample, True)
# update the running MD5 sum calculation with the frame's data
self.current_md5sum.update(framelist.to_bytes(0, 1))
# and finally return the frame data
return framelist
def read_frame_header(self):
crc8 = CRC8()
self.reader.add_callback(crc8.update)
# read the 32-bit FLAC frame header
sync_code = self.reader.read(14)
if (sync_code != 0x3FFE):
raise ValueError("invalid sync code")
self.reader.skip(1)
blocking_strategy = self.reader.read(1)
block_size_bits = self.reader.read(4)
sample_rate_bits = self.reader.read(4)
channel_assignment = self.reader.read(4)
bits_per_sample_bits = self.reader.read(3)
self.reader.skip(1)
# the frame number is a UTF-8 encoded value
# which takes a variable number of whole bytes
frame_number = self.read_utf8()
# unpack the 4 bit block size field
# which is the total PCM frames in the FLAC frame
# and may require up to 16 more bits if the frame is usually-sized
# (which typically happens at the end of the stream)
if (block_size_bits == 0x6):
block_size = self.reader.read(8) + 1
elif (block_size_bits == 0x7):
block_size = self.reader.read(16) + 1
else:
block_size = self.BLOCK_SIZE[block_size_bits]
# unpack the 4 bit sample rate field
# which is used for playback, but not needed for decoding
# and may require up to 16 more bits
# if the stream has a particularly unusual sample rate
if (sample_rate_bits == 0xC):
sample_rate = self.reader.read(8) * 1000
elif (sample_rate_bits == 0xD):
sample_rate = self.reader.read(16)
elif (sample_rate_bits == 0xE):
sample_rate = self.reader.read(16) * 10
elif (sample_rate_bits == 0xF):
raise ValueError("invalid sample rate")
else:
sample_rate = self.SAMPLE_RATE[sample_rate_bits]
# unpack the 3 bit bits-per-sample field
# this never requires additional bits
if ((bits_per_sample_bits == 0x3) or (bits_per_sample_bits == 0x7)):
raise ValueError("invalid bits per sample")
else:
bits_per_sample = self.BITS_PER_SAMPLE[bits_per_sample_bits]
# read and verify frame's CRC-8 value
self.reader.read(8)
self.reader.pop_callback()
if (int(crc8) != 0):
raise ValueError("CRC8 mismatch in frame header")
return (block_size, channel_assignment, bits_per_sample)
def read_subframe_header(self):
"""returns a tuple of (subframe_type, subframe_order, wasted_bps)"""
self.reader.skip(1)
subframe_type = self.reader.read(6)
if (self.reader.read(1) == 1):
wasted_bps = self.reader.unary(1) + 1
else:
wasted_bps = 0
# extract "order" value from 6 bit subframe type, if necessary
if (subframe_type == 0):
return (self.SUBFRAME_CONSTANT, None, wasted_bps)
elif (subframe_type == 1):
return (self.SUBFRAME_VERBATIM, None, wasted_bps)
elif ((subframe_type & 0x38) == 0x08):
return (self.SUBFRAME_FIXED, subframe_type & 0x07, wasted_bps)
elif ((subframe_type & 0x20) == 0x20):
return (self.SUBFRAME_LPC, (subframe_type & 0x1F) + 1, wasted_bps)
else:
raise ValueError("invalid subframe type")
def read_subframe(self, block_size, bits_per_sample):
(subframe_type, subframe_order,
wasted_bps) = self.read_subframe_header()
# read a list of signed sample values
# depending on the subframe type, block size,
# adjusted bits per sample and optional subframe order
if (subframe_type == self.SUBFRAME_CONSTANT):
subframe_samples = self.read_constant_subframe(
block_size, bits_per_sample - wasted_bps)
elif (subframe_type == self.SUBFRAME_VERBATIM):
subframe_samples = self.read_verbatim_subframe(
block_size, bits_per_sample - wasted_bps)
elif (subframe_type == self.SUBFRAME_FIXED):
subframe_samples = self.read_fixed_subframe(
block_size, bits_per_sample - wasted_bps, subframe_order)
else:
subframe_samples = self.read_lpc_subframe(
block_size, bits_per_sample - wasted_bps, subframe_order)
# account for wasted bits-per-sample, if necessary
if (wasted_bps):
return [sample << wasted_bps for sample in subframe_samples]
else:
return subframe_samples
def read_constant_subframe(self, block_size, bits_per_sample):
sample = self.reader.read_signed(bits_per_sample)
return [sample] * block_size
def read_verbatim_subframe(self, block_size, bits_per_sample):
return [
self.reader.read_signed(bits_per_sample) for x in range(block_size)
]
def read_fixed_subframe(self, block_size, bits_per_sample, order):
# "order" number of warm-up samples
samples = [
self.reader.read_signed(bits_per_sample) for i in range(order)
]
# "block_size" - "order" number of residual values
residuals = self.read_residual(block_size, order)
# which are applied to the warm-up samples
# depending on the FIXED subframe order
# and results in "block_size" number of total samples
if (order == 0):
return residuals
elif (order == 1):
for residual in residuals:
samples.append(samples[-1] + residual)
return samples
elif (order == 2):
for residual in residuals:
samples.append((2 * samples[-1]) - samples[-2] + residual)
return samples
elif (order == 3):
for residual in residuals:
samples.append((3 * samples[-1]) - (3 * samples[-2]) +
samples[-3] + residual)
return samples
elif (order == 4):
for residual in residuals:
samples.append((4 * samples[-1]) - (6 * samples[-2]) +
(4 * samples[-3]) - samples[-4] + residual)
return samples
else:
raise ValueError("unsupported FIXED subframe order")
def read_lpc_subframe(self, block_size, bits_per_sample, order):
# "order" number of warm-up samples
samples = [
self.reader.read_signed(bits_per_sample) for i in range(order)
]
# the size of each QLP coefficient, in bits
qlp_precision = self.reader.read(4)
# the amount of right shift to apply
# during LPC calculation
# (though this is a signed value, negative shifts are noops
# in the reference FLAC decoder)
qlp_shift_needed = max(self.reader.read_signed(5), 0)
# "order" number of signed QLP coefficients
qlp_coeffs = [
self.reader.read_signed(qlp_precision + 1) for i in range(order)
]
# QLP coefficients are applied in reverse order
qlp_coeffs.reverse()
# "block_size" - "order" number of residual values
residuals = self.read_residual(block_size, order)
# which are applied to the running LPC calculation
for residual in residuals:
samples.append((sum([
coeff * sample
for (coeff, sample) in zip(qlp_coeffs, samples[-order:])
]) >> qlp_shift_needed) + residual)
return samples
def read_residual(self, block_size, order):
residuals = []
coding_method = self.reader.read(2)
partition_order = self.reader.read(4)
# each parititon contains block_size / 2 ** partition_order
# number of residuals
for partition_number in range(2**partition_order):
if (partition_number == 0):
# except for the first partition
# which contains "order" less than the rest
residuals.extend(
self.read_residual_partition(
coding_method,
(block_size // 2**partition_order) - order))
else:
residuals.extend(
self.read_residual_partition(
coding_method, block_size // 2**partition_order))
return residuals
def read_residual_partition(self, coding_method, residual_count):
if (coding_method == 0):
# the Rice parameters determines the number of
# least-significant bits to read for each residual
rice_parameter = self.reader.read(4)
if (rice_parameter == 0xF):
escape_code = self.reader.read(5)
return [
self.reader.read_signed(escape_code)
for i in range(residual_count)
]
elif (coding_method == 1):
# 24 bps streams may use a 5-bit Rice parameter
# for better compression
rice_parameter = self.reader.read(5)
if (rice_parameter == 0x1F):
escape_code = self.reader.read(5)
return [
self.reader.read_signed(escape_code)
for i in range(residual_count)
]
else:
raise ValueError("invalid Rice coding parameter")
# a list of signed residual values
partition_residuals = []
for i in range(residual_count):
msb = self.reader.unary(1) # most-significant bits
lsb = self.reader.read(rice_parameter) # least-significant bits
value = (msb << rice_parameter) | lsb # combined into a value
if (value & 1): # whose least-significant bit is the sign value
partition_residuals.append(-(value >> 1) - 1)
else:
partition_residuals.append(value >> 1)
return partition_residuals
def read_utf8(self):
total_bytes = self.reader.unary(0)
value = self.reader.read(7 - total_bytes)
while (total_bytes > 1):
value = ((value << 6) | self.reader.parse("2p 6u")[0])
total_bytes -= 1
return value
def close(self):
self.reader.close()
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, traceback):
self.close()
