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 ALACDecoder:
def __init__(self, filename):
self.reader = BitstreamReader(open(filename, "rb"), 0)
self.reader.mark()
try:
#locate the "alac" atom
#which is full of required decoding parameters
try:
stsd = self.find_sub_atom("moov", "trak", "mdia",
"minf", "stbl", "stsd")
except KeyError:
raise ValueError("required stsd atom not found")
(stsd_version, descriptions) = stsd.parse("8u 24p 32u")
(alac1,
alac2,
self.samples_per_frame,
self.bits_per_sample,
self.history_multiplier,
self.initial_history,
self.maximum_k,
self.channels,
self.sample_rate) = stsd.parse(
#ignore much of the stuff in the "high" ALAC atom
"32p 4b 6P 16p 16p 16p 4P 16p 16p 16p 16p 4P" +
#and use the attributes in the "low" ALAC atom instead
"32p 4b 4P 32u 8p 8u 8u 8u 8u 8u 16p 32p 32p 32u")
self.channel_mask = {1: 0x0004,
2: 0x0003,
3: 0x0007,
4: 0x0107,
5: 0x0037,
6: 0x003F,
7: 0x013F,
8: 0x00FF}.get(self.channels, 0)
if ((alac1 != 'alac') or (alac2 != 'alac')):
raise ValueError("Invalid alac atom")
#also locate the "mdhd" atom
#which contains the stream's length in PCM frames
self.reader.rewind()
mdhd = self.find_sub_atom("moov", "trak", "mdia", "mdhd")
(version, ) = mdhd.parse("8u 24p")
if (version == 0):
(self.total_pcm_frames,) = mdhd.parse(
"32p 32p 32p 32u 2P 16p")
elif (version == 1):
(self.total_pcm_frames,) = mdhd.parse(
"64p 64p 32p 64U 2P 16p")
else:
raise ValueError("invalid mdhd version")
#finally, set our stream to the "mdat" atom
self.reader.rewind()
(atom_size, atom_name) = self.reader.parse("32u 4b")
while (atom_name != "mdat"):
self.reader.skip_bytes(atom_size - 8)
(atom_size, atom_name) = self.reader.parse("32u 4b")
finally:
self.reader.unmark()
def find_sub_atom(self, *atom_names):
reader = self.reader
for (last, next_atom) in iter_last(iter(atom_names)):
try:
(length, stream_atom) = reader.parse("32u 4b")
while (stream_atom != next_atom):
reader.skip_bytes(length - 8)
(length, stream_atom) = reader.parse("32u 4b")
if (last):
return reader.substream(length - 8)
else:
reader = reader.substream(length - 8)
except IOError:
raise KeyError(next_atom)
def read(self, pcm_frames):
#if the stream is exhausted, return an empty pcm.FrameList object
if (self.total_pcm_frames == 0):
return from_list([], self.channels, self.bits_per_sample, True)
#otherwise, read one ALAC frameset's worth of frame data
frameset_data = []
frame_channels = self.reader.read(3) + 1
while (frame_channels != 0x8):
frameset_data.extend(self.read_frame(frame_channels))
frame_channels = self.reader.read(3) + 1
self.reader.byte_align()
#reorder the frameset to Wave order, depending on channel count
if ((self.channels == 1) or (self.channels == 2)):
pass
elif (self.channels == 3):
frameset_data = [frameset_data[1],
frameset_data[2],
frameset_data[0]]
elif (self.channels == 4):
frameset_data = [frameset_data[1],
frameset_data[2],
frameset_data[0],
frameset_data[3]]
elif (self.channels == 5):
frameset_data = [frameset_data[1],
frameset_data[2],
frameset_data[0],
frameset_data[3],
frameset_data[4]]
elif (self.channels == 6):
frameset_data = [frameset_data[1],
frameset_data[2],
frameset_data[0],
frameset_data[5],
frameset_data[3],
frameset_data[4]]
elif (self.channels == 7):
frameset_data = [frameset_data[1],
frameset_data[2],
frameset_data[0],
frameset_data[6],
frameset_data[3],
frameset_data[4],
frameset_data[5]]
elif (self.channels == 8):
frameset_data = [frameset_data[3],
frameset_data[4],
frameset_data[0],
frameset_data[7],
frameset_data[5],
frameset_data[6],
frameset_data[1],
frameset_data[2]]
else:
raise ValueError("unsupported channel count")
framelist = from_channels([from_list(channel,
1,
self.bits_per_sample,
True)
for channel in frameset_data])
#deduct PCM frames from remainder
self.total_pcm_frames -= framelist.frames
#return samples as a pcm.FrameList object
return framelist
def read_frame(self, channel_count):
"""returns a list of PCM sample lists, one per channel"""
#read the ALAC frame header
self.reader.skip(16)
has_sample_count = self.reader.read(1)
uncompressed_lsb_size = self.reader.read(2)
uncompressed = self.reader.read(1)
if (has_sample_count):
sample_count = self.reader.read(32)
else:
sample_count = self.samples_per_frame
if (uncompressed == 1):
#if the frame is uncompressed,
#read the raw, interlaced samples
samples = [self.reader.read_signed(self.bits_per_sample)
for i in xrange(sample_count * channel_count)]
return [samples[i::channel_count] for i in xrange(channel_count)]
else:
#if the frame is compressed,
#read the interlacing parameters
interlacing_shift = self.reader.read(8)
interlacing_leftweight = self.reader.read(8)
#subframe headers
subframe_headers = [self.read_subframe_header()
for i in xrange(channel_count)]
#optional uncompressed LSB values
if (uncompressed_lsb_size > 0):
uncompressed_lsbs = [
self.reader.read(uncompressed_lsb_size * 8)
for i in xrange(sample_count * channel_count)]
else:
uncompressed_lsbs = []
sample_size = (self.bits_per_sample -
(uncompressed_lsb_size * 8) +
channel_count - 1)
#and residual blocks
residual_blocks = [self.read_residuals(sample_size,
sample_count)
for i in xrange(channel_count)]
#calculate subframe samples based on
#subframe header's QLP coefficients and QLP shift-needed
decoded_subframes = [self.decode_subframe(header[0],
header[1],
sample_size,
residuals)
for (header, residuals) in
zip(subframe_headers,
residual_blocks)]
#decorrelate channels according interlacing shift and leftweight
decorrelated_channels = self.decorrelate_channels(
decoded_subframes,
interlacing_shift,
interlacing_leftweight)
#if uncompressed LSB values are present,
#prepend them to each sample of each channel
if (uncompressed_lsb_size > 0):
channels = []
for (i, channel) in enumerate(decorrelated_channels):
assert(len(channel) ==
len(uncompressed_lsbs[i::channel_count]))
channels.append([s << (uncompressed_lsb_size * 8) | l
for (s, l) in
zip(channel,
uncompressed_lsbs[i::channel_count])])
return channels
else:
return decorrelated_channels
def read_subframe_header(self):
prediction_type = self.reader.read(4)
qlp_shift_needed = self.reader.read(4)
rice_modifier = self.reader.read(3)
qlp_coefficients = [self.reader.read_signed(16)
for i in xrange(self.reader.read(5))]
return (qlp_shift_needed, qlp_coefficients)
def read_residuals(self, sample_size, sample_count):
residuals = []
history = self.initial_history
sign_modifier = 0
i = 0
while (i < sample_count):
#get an unsigned residual based on "history"
#and on "sample_size" as a lst resort
k = min(log2(history / (2 ** 9) + 3), self.maximum_k)
unsigned = self.read_residual(k, sample_size) + sign_modifier
#clear out old sign modifier, if any
sign_modifier = 0
#change unsigned residual to signed residual
if (unsigned & 1):
residuals.append(-((unsigned + 1) / 2))
else:
residuals.append(unsigned / 2)
#update history based on unsigned residual
if (unsigned <= 0xFFFF):
history += ((unsigned * self.history_multiplier) -
((history * self.history_multiplier) >> 9))
else:
history = 0xFFFF
#if history gets too small, we may have a block of 0 samples
#which can be compressed more efficiently
if ((history < 128) and ((i + 1) < sample_count)):
zeroes_k = min(7 -
log2(history) +
((history + 16) / 64),
self.maximum_k)
zero_residuals = self.read_residual(zeroes_k, 16)
if (zero_residuals > 0):
residuals.extend([0] * zero_residuals)
i += zero_residuals
history = 0
if (zero_residuals <= 0xFFFF):
sign_modifier = 1
i += 1
return residuals
def read_residual(self, k, sample_size):
msb = self.reader.limited_unary(0, 9)
if (msb is None):
return self.reader.read(sample_size)
elif (k == 0):
return msb
else:
lsb = self.reader.read(k)
if (lsb > 1):
return msb * ((1 << k) - 1) + (lsb - 1)
elif (lsb == 1):
self.reader.unread(1)
return msb * ((1 << k) - 1)
else:
self.reader.unread(0)
return msb * ((1 << k) - 1)
def decode_subframe(self, qlp_shift_needed, qlp_coefficients,
sample_size, residuals):
#first sample is always copied verbatim
samples = [residuals.pop(0)]
if (len(qlp_coefficients) < 31):
#the next "coefficient count" samples
#are applied as differences to the previous
for i in xrange(len(qlp_coefficients)):
samples.append(truncate_bits(samples[-1] + residuals.pop(0),
sample_size))
#remaining samples are processed much like LPC
for residual in residuals:
base_sample = samples[-len(qlp_coefficients) - 1]
lpc_sum = sum([(s - base_sample) * c for (s, c) in
zip(samples[-len(qlp_coefficients):],
reversed(qlp_coefficients))])
outval = (1 << (qlp_shift_needed - 1)) + lpc_sum
outval >>= qlp_shift_needed
samples.append(truncate_bits(outval + residual + base_sample,
sample_size))
buf = samples[-len(qlp_coefficients) - 2:-1]
#error value then adjusts the coefficients table
if (residual > 0):
predictor_num = len(qlp_coefficients) - 1
while ((predictor_num >= 0) and residual > 0):
val = (buf[0] -
buf[len(qlp_coefficients) - predictor_num])
sign = sign_only(val)
qlp_coefficients[predictor_num] -= sign
val *= sign
residual -= ((val >> qlp_shift_needed) *
(len(qlp_coefficients) - predictor_num))
predictor_num -= 1
elif (residual < 0):
#the same as above, but we break if residual goes positive
predictor_num = len(qlp_coefficients) - 1
while ((predictor_num >= 0) and residual < 0):
val = (buf[0] -
buf[len(qlp_coefficients) - predictor_num])
sign = -sign_only(val)
qlp_coefficients[predictor_num] -= sign
val *= sign
residual -= ((val >> qlp_shift_needed) *
(len(qlp_coefficients) - predictor_num))
predictor_num -= 1
else:
#residuals are encoded as simple difference values
for residual in residuals:
samples.append(truncate_bits(samples[-1] + residual,
sample_size))
return samples
def decorrelate_channels(self, channel_data,
interlacing_shift, interlacing_leftweight):
if (len(channel_data) != 2):
return channel_data
elif (interlacing_leftweight == 0):
return channel_data
else:
left = []
right = []
for (ch1, ch2) in zip(*channel_data):
right.append(ch1 - ((ch2 * interlacing_leftweight) /
(2 ** interlacing_shift)))
left.append(ch2 + right[-1])
return [left, right]
def close(self):
pass
class ALACDecoder(object):
def __init__(self, filename):
self.reader = BitstreamReader(open(filename, "rb"), False)
self.reader.mark()
try:
# locate the "alac" atom
# which is full of required decoding parameters
try:
stsd = self.find_sub_atom(b"moov", b"trak", b"mdia", b"minf",
b"stbl", b"stsd")
except KeyError:
raise ValueError("required stsd atom not found")
(stsd_version, descriptions) = stsd.parse("8u 24p 32u")
(alac1, alac2, self.samples_per_frame, self.bits_per_sample,
self.history_multiplier, self.initial_history, self.maximum_k,
self.channels, self.sample_rate) = stsd.parse(
# ignore much of the stuff in the "high" ALAC atom
"32p 4b 6P 16p 16p 16p 4P 16p 16p 16p 16p 4P" +
# and use the attributes in the "low" ALAC atom instead
"32p 4b 4P 32u 8p 8u 8u 8u 8u 8u 16p 32p 32p 32u")
self.channel_mask = {
1: 0x0004,
2: 0x0003,
3: 0x0007,
4: 0x0107,
5: 0x0037,
6: 0x003F,
7: 0x013F,
8: 0x00FF
}.get(self.channels, 0)
if ((alac1 != b'alac') or (alac2 != b'alac')):
raise ValueError("Invalid alac atom")
# also locate the "mdhd" atom
# which contains the stream's length in PCM frames
self.reader.rewind()
mdhd = self.find_sub_atom(b"moov", b"trak", b"mdia", b"mdhd")
(version, ) = mdhd.parse("8u 24p")
if (version == 0):
(self.total_pcm_frames,
) = mdhd.parse("32p 32p 32p 32u 2P 16p")
elif (version == 1):
(self.total_pcm_frames,
) = mdhd.parse("64p 64p 32p 64U 2P 16p")
else:
raise ValueError("invalid mdhd version")
# finally, set our stream to the "mdat" atom
self.reader.rewind()
(atom_size, atom_name) = self.reader.parse("32u 4b")
while (atom_name != b"mdat"):
self.reader.skip_bytes(atom_size - 8)
(atom_size, atom_name) = self.reader.parse("32u 4b")
finally:
self.reader.unmark()
def find_sub_atom(self, *atom_names):
reader = self.reader
for (last, next_atom) in iter_last(iter(atom_names)):
try:
(length, stream_atom) = reader.parse("32u 4b")
while (stream_atom != next_atom):
reader.skip_bytes(length - 8)
(length, stream_atom) = reader.parse("32u 4b")
if (last):
return reader.substream(length - 8)
else:
reader = reader.substream(length - 8)
except IOError:
raise KeyError(next_atom)
def read(self, pcm_frames):
# if the stream is exhausted, return an empty pcm.FrameList object
if (self.total_pcm_frames == 0):
return empty_framelist(self.channels, self.bits_per_sample)
# otherwise, read one ALAC frameset's worth of frame data
frameset_data = []
frame_channels = self.reader.read(3) + 1
while (frame_channels != 0x8):
frameset_data.extend(self.read_frame(frame_channels))
frame_channels = self.reader.read(3) + 1
self.reader.byte_align()
# reorder the frameset to Wave order, depending on channel count
if ((self.channels == 1) or (self.channels == 2)):
pass
elif (self.channels == 3):
frameset_data = [
frameset_data[1], frameset_data[2], frameset_data[0]
]
elif (self.channels == 4):
frameset_data = [
frameset_data[1], frameset_data[2], frameset_data[0],
frameset_data[3]
]
elif (self.channels == 5):
frameset_data = [
frameset_data[1], frameset_data[2], frameset_data[0],
frameset_data[3], frameset_data[4]
]
elif (self.channels == 6):
frameset_data = [
frameset_data[1], frameset_data[2], frameset_data[0],
frameset_data[5], frameset_data[3], frameset_data[4]
]
elif (self.channels == 7):
frameset_data = [
frameset_data[1], frameset_data[2], frameset_data[0],
frameset_data[6], frameset_data[3], frameset_data[4],
frameset_data[5]
]
elif (self.channels == 8):
frameset_data = [
frameset_data[3], frameset_data[4], frameset_data[0],
frameset_data[7], frameset_data[5], frameset_data[6],
frameset_data[1], frameset_data[2]
]
else:
raise ValueError("unsupported channel count")
framelist = from_channels([
from_list(channel, 1, self.bits_per_sample, True)
for channel in frameset_data
])
# deduct PCM frames from remainder
self.total_pcm_frames -= framelist.frames
# return samples as a pcm.FrameList object
return framelist
def read_frame(self, channel_count):
"""returns a list of PCM sample lists, one per channel"""
# read the ALAC frame header
self.reader.skip(16)
has_sample_count = self.reader.read(1)
uncompressed_lsb_size = self.reader.read(2)
uncompressed = self.reader.read(1)
if (has_sample_count):
sample_count = self.reader.read(32)
else:
sample_count = self.samples_per_frame
if (uncompressed == 1):
# if the frame is uncompressed,
# read the raw, interlaced samples
samples = [
self.reader.read_signed(self.bits_per_sample)
for i in range(sample_count * channel_count)
]
return [samples[i::channel_count] for i in range(channel_count)]
else:
# if the frame is compressed,
# read the interlacing parameters
interlacing_shift = self.reader.read(8)
interlacing_leftweight = self.reader.read(8)
# subframe headers
subframe_headers = [
self.read_subframe_header() for i in range(channel_count)
]
# optional uncompressed LSB values
if (uncompressed_lsb_size > 0):
uncompressed_lsbs = [
self.reader.read(uncompressed_lsb_size * 8)
for i in range(sample_count * channel_count)
]
else:
uncompressed_lsbs = []
sample_size = (self.bits_per_sample - (uncompressed_lsb_size * 8) +
channel_count - 1)
# and residual blocks
residual_blocks = [
self.read_residuals(sample_size, sample_count)
for i in range(channel_count)
]
# calculate subframe samples based on
# subframe header's QLP coefficients and QLP shift-needed
decoded_subframes = [
self.decode_subframe(header[0], header[1], sample_size,
residuals)
for (header,
residuals) in zip(subframe_headers, residual_blocks)
]
# decorrelate channels according interlacing shift and leftweight
decorrelated_channels = self.decorrelate_channels(
decoded_subframes, interlacing_shift, interlacing_leftweight)
# if uncompressed LSB values are present,
# prepend them to each sample of each channel
if (uncompressed_lsb_size > 0):
channels = []
for (i, channel) in enumerate(decorrelated_channels):
assert (len(channel) == len(
uncompressed_lsbs[i::channel_count]))
channels.append([
s << (uncompressed_lsb_size * 8) | l for (s, l) in zip(
channel, uncompressed_lsbs[i::channel_count])
])
return channels
else:
return decorrelated_channels
def read_subframe_header(self):
prediction_type = self.reader.read(4)
qlp_shift_needed = self.reader.read(4)
rice_modifier = self.reader.read(3)
qlp_coefficients = [
self.reader.read_signed(16) for i in range(self.reader.read(5))
]
return (qlp_shift_needed, qlp_coefficients)
def read_residuals(self, sample_size, sample_count):
residuals = []
history = self.initial_history
sign_modifier = 0
i = 0
while (i < sample_count):
# get an unsigned residual based on "history"
# and on "sample_size" as a lst resort
k = min(log2(history // (2**9) + 3), self.maximum_k)
unsigned = self.read_residual(k, sample_size) + sign_modifier
# clear out old sign modifier, if any
sign_modifier = 0
# change unsigned residual to signed residual
if (unsigned & 1):
residuals.append(-((unsigned + 1) // 2))
else:
residuals.append(unsigned // 2)
# update history based on unsigned residual
if (unsigned <= 0xFFFF):
history += ((unsigned * self.history_multiplier) -
((history * self.history_multiplier) >> 9))
else:
history = 0xFFFF
# if history gets too small, we may have a block of 0 samples
# which can be compressed more efficiently
if ((history < 128) and ((i + 1) < sample_count)):
zeroes_k = min(7 - log2(history) + ((history + 16) // 64),
self.maximum_k)
zero_residuals = self.read_residual(zeroes_k, 16)
if (zero_residuals > 0):
residuals.extend([0] * zero_residuals)
i += zero_residuals
history = 0
if (zero_residuals <= 0xFFFF):
sign_modifier = 1
i += 1
return residuals
def read_residual(self, k, sample_size):
msb = self.reader.read_huffman_code(RESIDUAL)
if (msb == -1):
return self.reader.read(sample_size)
elif (k == 0):
return msb
else:
lsb = self.reader.read(k)
if (lsb > 1):
return msb * ((1 << k) - 1) + (lsb - 1)
elif (lsb == 1):
self.reader.unread(1)
return msb * ((1 << k) - 1)
else:
self.reader.unread(0)
return msb * ((1 << k) - 1)
def decode_subframe(self, qlp_shift_needed, qlp_coefficients, sample_size,
residuals):
# first sample is always copied verbatim
samples = [residuals.pop(0)]
if (len(qlp_coefficients) < 31):
# the next "coefficient count" samples
# are applied as differences to the previous
for i in range(len(qlp_coefficients)):
samples.append(
truncate_bits(samples[-1] + residuals.pop(0), sample_size))
# remaining samples are processed much like LPC
for residual in residuals:
base_sample = samples[-len(qlp_coefficients) - 1]
lpc_sum = sum([(s - base_sample) * c
for (s,
c) in zip(samples[-len(qlp_coefficients):],
reversed(qlp_coefficients))])
outval = (1 << (qlp_shift_needed - 1)) + lpc_sum
outval >>= qlp_shift_needed
samples.append(
truncate_bits(outval + residual + base_sample,
sample_size))
buf = samples[-len(qlp_coefficients) - 2:-1]
# error value then adjusts the coefficients table
if (residual > 0):
predictor_num = len(qlp_coefficients) - 1
while ((predictor_num >= 0) and residual > 0):
val = (buf[0] -
buf[len(qlp_coefficients) - predictor_num])
sign = sign_only(val)
qlp_coefficients[predictor_num] -= sign
val *= sign
residual -= ((val >> qlp_shift_needed) *
(len(qlp_coefficients) - predictor_num))
predictor_num -= 1
elif (residual < 0):
# the same as above, but we break if residual goes positive
predictor_num = len(qlp_coefficients) - 1
while ((predictor_num >= 0) and residual < 0):
val = (buf[0] -
buf[len(qlp_coefficients) - predictor_num])
sign = -sign_only(val)
qlp_coefficients[predictor_num] -= sign
val *= sign
residual -= ((val >> qlp_shift_needed) *
(len(qlp_coefficients) - predictor_num))
predictor_num -= 1
else:
# residuals are encoded as simple difference values
for residual in residuals:
samples.append(
truncate_bits(samples[-1] + residual, sample_size))
return samples
def decorrelate_channels(self, channel_data, interlacing_shift,
interlacing_leftweight):
if (len(channel_data) != 2):
return channel_data
elif (interlacing_leftweight == 0):
return channel_data
else:
left = []
right = []
for (ch1, ch2) in zip(*channel_data):
right.append(ch1 - ((ch2 * interlacing_leftweight) //
(2**interlacing_shift)))
left.append(ch2 + right[-1])
return [left, right]
def close(self):
self.reader.close()
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, traceback):
self.close()
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()