def __find_next_mp3_frame__(cls, mp3file):
from audiotools.id3 import skip_id3v2_comment
# if we're starting at an ID3v2 header, skip it to save a bunch of time
bytes_skipped = skip_id3v2_comment(mp3file)
# then find the next mp3 frame
from audiotools.bitstream import BitstreamReader
reader = BitstreamReader(mp3file, False)
pos = reader.getpos()
try:
(sync, mpeg_id, layer_description) = reader.parse("11u 2u 2u 1p")
except IOError as err:
raise err
while (not ((sync == 0x7FF) and (mpeg_id in (0, 2, 3)) and
(layer_description in (1, 2, 3)))):
reader.setpos(pos)
reader.skip(8)
bytes_skipped += 1
pos = reader.getpos()
try:
(sync, mpeg_id,
layer_description) = reader.parse("11u 2u 2u 1p")
except IOError as err:
raise err
else:
reader.setpos(pos)
return bytes_skipped
def __find_next_mp3_frame__(cls, mp3file):
from audiotools.id3 import skip_id3v2_comment
# if we're starting at an ID3v2 header, skip it to save a bunch of time
bytes_skipped = skip_id3v2_comment(mp3file)
# then find the next mp3 frame
from audiotools.bitstream import BitstreamReader
reader = BitstreamReader(mp3file, False)
pos = reader.getpos()
try:
(sync,
mpeg_id,
layer_description) = reader.parse("11u 2u 2u 1p")
except IOError as err:
raise err
while (not ((sync == 0x7FF) and
(mpeg_id in (0, 2, 3)) and
(layer_description in (1, 2, 3)))):
reader.setpos(pos)
reader.skip(8)
bytes_skipped += 1
pos = reader.getpos()
try:
(sync,
mpeg_id,
layer_description) = reader.parse("11u 2u 2u 1p")
except IOError as err:
raise err
else:
reader.setpos(pos)
return bytes_skipped
def __find_mp3_start__(cls, mp3file):
"""places mp3file at the position of the MP3 file's start"""
from audiotools.id3 import skip_id3v2_comment
# if we're starting at an ID3v2 header, skip it to save a bunch of time
skip_id3v2_comment(mp3file)
from audiotools.bitstream import BitstreamReader
reader = BitstreamReader(mp3file, False)
# skip over any bytes that aren't a valid MPEG header
pos = reader.getpos()
(frame_sync, mpeg_id, layer) = reader.parse("11u 2u 2u 1p")
while (not ((frame_sync == 0x7FF) and (mpeg_id in (0, 2, 3)) and
(layer in (1, 2, 3)))):
reader.setpos(pos)
reader.skip(8)
pos = reader.getpos()
reader.setpos(pos)
def __find_mp3_start__(cls, mp3file):
"""places mp3file at the position of the MP3 file's start"""
from audiotools.id3 import skip_id3v2_comment
# if we're starting at an ID3v2 header, skip it to save a bunch of time
skip_id3v2_comment(mp3file)
from audiotools.bitstream import BitstreamReader
reader = BitstreamReader(mp3file, False)
# skip over any bytes that aren't a valid MPEG header
pos = reader.getpos()
(frame_sync, mpeg_id, layer) = reader.parse("11u 2u 2u 1p")
while (not ((frame_sync == 0x7FF) and
(mpeg_id in (0, 2, 3)) and
(layer in (1, 2, 3)))):
reader.setpos(pos)
reader.skip(8)
pos = reader.getpos()
reader.setpos(pos)
class WaveReader(object):
"""a PCMReader object for reading wave file contents"""
def __init__(self, wave_filename):
"""wave_filename is a string"""
from audiotools.bitstream import BitstreamReader
self.stream = BitstreamReader(open(wave_filename, "rb"), True)
# ensure RIFF<size>WAVE header is ok
try:
(riff,
total_size,
wave) = self.stream.parse("4b 32u 4b")
except struct.error:
from audiotools.text import ERR_WAV_INVALID_WAVE
self.stream.close()
raise ValueError(ERR_WAV_INVALID_WAVE)
if riff != b'RIFF':
from audiotools.text import ERR_WAV_NOT_WAVE
self.stream.close()
raise ValueError(ERR_WAV_NOT_WAVE)
elif wave != b'WAVE':
from audiotools.text import ERR_WAV_INVALID_WAVE
self.stream.close()
raise ValueError(ERR_WAV_INVALID_WAVE)
else:
total_size -= 4
fmt_chunk_read = False
# walk through chunks until "data" chunk encountered
while total_size > 0:
try:
(chunk_id,
chunk_size) = self.stream.parse("4b 32u")
except struct.error:
from audiotools.text import ERR_WAV_INVALID_WAVE
self.stream.close()
raise ValueError(ERR_WAV_INVALID_WAVE)
if not frozenset(chunk_id).issubset(WaveAudio.PRINTABLE_ASCII):
from audiotools.text import ERR_WAV_INVALID_CHUNK
self.stream.close()
raise ValueError(ERR_WAV_INVALID_CHUNK)
else:
total_size -= 8
if chunk_id == b"fmt ":
# when "fmt " chunk encountered,
# use it to populate PCMReader attributes
(self.channels,
self.sample_rate,
self.bits_per_sample,
channel_mask) = parse_fmt(self.stream)
self.channel_mask = int(channel_mask)
self.bytes_per_pcm_frame = ((self.bits_per_sample // 8) *
self.channels)
fmt_chunk_read = True
elif chunk_id == b"data":
# when "data" chunk encountered,
# use its size to determine total PCM frames
# and ready PCMReader for reading
if not fmt_chunk_read:
from audiotools.text import ERR_WAV_PREMATURE_DATA
self.stream.close()
raise ValueError(ERR_WAV_PREMATURE_DATA)
else:
self.total_pcm_frames = (chunk_size //
self.bytes_per_pcm_frame)
self.remaining_pcm_frames = self.total_pcm_frames
self.data_start = self.stream.getpos()
return
else:
# all other chunks are ignored
self.stream.skip_bytes(chunk_size)
if chunk_size % 2:
if len(self.stream.read_bytes(1)) < 1:
from audiotools.text import ERR_WAV_INVALID_CHUNK
self.stream.close()
raise ValueError(ERR_WAV_INVALID_CHUNK)
total_size -= (chunk_size + 1)
else:
total_size -= chunk_size
else:
# raise an error if no "data" chunk is encountered
from audiotools.text import ERR_WAV_NO_DATA_CHUNK
self.stream.close()
raise ValueError(ERR_WAV_NO_DATA_CHUNK)
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, traceback):
self.close()
def read(self, pcm_frames):
"""try to read a pcm.FrameList with the given number of PCM frames"""
# try to read requested PCM frames or remaining frames
requested_pcm_frames = min(max(pcm_frames, 1),
self.remaining_pcm_frames)
requested_bytes = (self.bytes_per_pcm_frame *
requested_pcm_frames)
pcm_data = self.stream.read_bytes(requested_bytes)
# raise exception if "data" chunk exhausted early
if len(pcm_data) < requested_bytes:
from audiotools.text import ERR_WAV_TRUNCATED_DATA_CHUNK
raise IOError(ERR_WAV_TRUNCATED_DATA_CHUNK)
else:
self.remaining_pcm_frames -= requested_pcm_frames
# return parsed chunk
return FrameList(pcm_data,
self.channels,
self.bits_per_sample,
False,
self.bits_per_sample != 8)
def read_closed(self, pcm_frames):
raise ValueError("cannot read closed stream")
def seek(self, pcm_frame_offset):
"""tries to seek to the given PCM frame offset
returns the total amount of frames actually seeked over"""
if pcm_frame_offset < 0:
from audiotools.text import ERR_NEGATIVE_SEEK
raise ValueError(ERR_NEGATIVE_SEEK)
# ensure one doesn't walk off the end of the file
pcm_frame_offset = min(pcm_frame_offset, self.total_pcm_frames)
# position file in "data" chunk
self.stream.setpos(self.data_start)
self.stream.seek(pcm_frame_offset * self.bytes_per_pcm_frame, 1)
self.remaining_pcm_frames = (self.total_pcm_frames -
pcm_frame_offset)
return pcm_frame_offset
def seek_closed(self, pcm_frame_offset):
raise ValueError("cannot seek closed stream")
def close(self):
"""closes the stream for reading"""
self.stream.close()
self.read = self.read_closed
self.seek = self.seek_closed
class AiffReader(object):
"""a PCMReader object for reading AIFF file contents"""
def __init__(self, aiff_filename):
"""aiff_filename is a string"""
from audiotools.bitstream import BitstreamReader
self.stream = BitstreamReader(open(aiff_filename, "rb"), False)
# ensure FORM<size>AIFF header is ok
try:
(form, total_size, aiff) = self.stream.parse("4b 32u 4b")
except struct.error:
from audiotools.text import ERR_AIFF_INVALID_AIFF
raise InvalidAIFF(ERR_AIFF_INVALID_AIFF)
if form != b'FORM':
from audiotools.text import ERR_AIFF_NOT_AIFF
raise ValueError(ERR_AIFF_NOT_AIFF)
elif aiff != b'AIFF':
from audiotools.text import ERR_AIFF_INVALID_AIFF
raise ValueError(ERR_AIFF_INVALID_AIFF)
else:
total_size -= 4
comm_chunk_read = False
# walk through chunks until "SSND" chunk encountered
while total_size > 0:
try:
(chunk_id, chunk_size) = self.stream.parse("4b 32u")
except struct.error:
from audiotools.text import ERR_AIFF_INVALID_AIFF
raise ValueError(ERR_AIFF_INVALID_AIFF)
if not frozenset(chunk_id).issubset(AiffAudio.PRINTABLE_ASCII):
from audiotools.text import ERR_AIFF_INVALID_CHUNK_ID
raise ValueError(ERR_AIFF_INVALID_CHUNK_ID)
else:
total_size -= 8
if chunk_id == b"COMM":
# when "COMM" chunk encountered,
# use it to populate PCMReader attributes
(self.channels, self.total_pcm_frames, self.bits_per_sample,
self.sample_rate, channel_mask) = parse_comm(self.stream)
self.channel_mask = int(channel_mask)
self.bytes_per_pcm_frame = ((self.bits_per_sample // 8) *
self.channels)
self.remaining_pcm_frames = self.total_pcm_frames
comm_chunk_read = True
elif chunk_id == b"SSND":
# when "SSND" chunk encountered,
# strip off the "offset" and "block_size" attributes
# and ready PCMReader for reading
if not comm_chunk_read:
from audiotools.text import ERR_AIFF_PREMATURE_SSND_CHUNK
raise ValueError(ERR_AIFF_PREMATURE_SSND_CHUNK)
else:
self.stream.skip_bytes(8)
self.ssnd_start = self.stream.getpos()
return
else:
# all other chunks are ignored
self.stream.skip_bytes(chunk_size)
if chunk_size % 2:
if len(self.stream.read_bytes(1)) < 1:
from audiotools.text import ERR_AIFF_INVALID_CHUNK
raise ValueError(ERR_AIFF_INVALID_CHUNK)
total_size -= (chunk_size + 1)
else:
total_size -= chunk_size
else:
# raise an error if no "SSND" chunk is encountered
from audiotools.text import ERR_AIFF_NO_SSND_CHUNK
raise ValueError(ERR_AIFF_NO_SSND_CHUNK)
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, traceback):
self.close()
def read(self, pcm_frames):
"""try to read a pcm.FrameList with the given number of PCM frames"""
# try to read requested PCM frames or remaining frames
requested_pcm_frames = min(max(pcm_frames, 1),
self.remaining_pcm_frames)
requested_bytes = (self.bytes_per_pcm_frame * requested_pcm_frames)
pcm_data = self.stream.read_bytes(requested_bytes)
# raise exception if "SSND" chunk exhausted early
if len(pcm_data) < requested_bytes:
from audiotools.text import ERR_AIFF_TRUNCATED_SSND_CHUNK
raise IOError(ERR_AIFF_TRUNCATED_SSND_CHUNK)
else:
self.remaining_pcm_frames -= requested_pcm_frames
# return parsed chunk
return FrameList(pcm_data, self.channels, self.bits_per_sample,
True, True)
def read_closed(self, pcm_frames):
raise ValueError("cannot read closed stream")
def seek(self, pcm_frame_offset):
"""tries to seek to the given PCM frame offset
returns the total amount of frames actually seeked over"""
if pcm_frame_offset < 0:
from audiotools.text import ERR_NEGATIVE_SEEK
raise ValueError(ERR_NEGATIVE_SEEK)
# ensure one doesn't walk off the end of the file
pcm_frame_offset = min(pcm_frame_offset, self.total_pcm_frames)
# position file in "SSND" chunk
self.stream.setpos(self.ssnd_start)
self.stream.seek((pcm_frame_offset * self.bytes_per_pcm_frame), 1)
self.remaining_pcm_frames = (self.total_pcm_frames - pcm_frame_offset)
return pcm_frame_offset
def seek_closed(self, pcm_frame_offset):
raise ValueError("cannot seek closed stream")
def close(self):
"""closes the stream for reading"""
self.stream.close()
self.read = self.read_closed
self.seek = self.seek_closed
class AiffReader(object):
"""a PCMReader object for reading AIFF file contents"""
def __init__(self, aiff_filename):
"""aiff_filename is a string"""
from audiotools.bitstream import BitstreamReader
self.stream = BitstreamReader(open(aiff_filename, "rb"), False)
# ensure FORM<size>AIFF header is ok
try:
(form,
total_size,
aiff) = self.stream.parse("4b 32u 4b")
except struct.error:
from audiotools.text import ERR_AIFF_INVALID_AIFF
raise InvalidAIFF(ERR_AIFF_INVALID_AIFF)
if form != b'FORM':
from audiotools.text import ERR_AIFF_NOT_AIFF
raise ValueError(ERR_AIFF_NOT_AIFF)
elif aiff != b'AIFF':
from audiotools.text import ERR_AIFF_INVALID_AIFF
raise ValueError(ERR_AIFF_INVALID_AIFF)
else:
total_size -= 4
comm_chunk_read = False
# walk through chunks until "SSND" chunk encountered
while total_size > 0:
try:
(chunk_id,
chunk_size) = self.stream.parse("4b 32u")
except struct.error:
from audiotools.text import ERR_AIFF_INVALID_AIFF
raise ValueError(ERR_AIFF_INVALID_AIFF)
if not frozenset(chunk_id).issubset(AiffAudio.PRINTABLE_ASCII):
from audiotools.text import ERR_AIFF_INVALID_CHUNK_ID
raise ValueError(ERR_AIFF_INVALID_CHUNK_ID)
else:
total_size -= 8
if chunk_id == b"COMM":
# when "COMM" chunk encountered,
# use it to populate PCMReader attributes
(self.channels,
self.total_pcm_frames,
self.bits_per_sample,
self.sample_rate,
channel_mask) = parse_comm(self.stream)
self.channel_mask = int(channel_mask)
self.bytes_per_pcm_frame = ((self.bits_per_sample // 8) *
self.channels)
self.remaining_pcm_frames = self.total_pcm_frames
comm_chunk_read = True
elif chunk_id == b"SSND":
# when "SSND" chunk encountered,
# strip off the "offset" and "block_size" attributes
# and ready PCMReader for reading
if not comm_chunk_read:
from audiotools.text import ERR_AIFF_PREMATURE_SSND_CHUNK
raise ValueError(ERR_AIFF_PREMATURE_SSND_CHUNK)
else:
self.stream.skip_bytes(8)
self.ssnd_start = self.stream.getpos()
return
else:
# all other chunks are ignored
self.stream.skip_bytes(chunk_size)
if chunk_size % 2:
if len(self.stream.read_bytes(1)) < 1:
from audiotools.text import ERR_AIFF_INVALID_CHUNK
raise ValueError(ERR_AIFF_INVALID_CHUNK)
total_size -= (chunk_size + 1)
else:
total_size -= chunk_size
else:
# raise an error if no "SSND" chunk is encountered
from audiotools.text import ERR_AIFF_NO_SSND_CHUNK
raise ValueError(ERR_AIFF_NO_SSND_CHUNK)
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, traceback):
self.close()
def read(self, pcm_frames):
"""try to read a pcm.FrameList with the given number of PCM frames"""
# try to read requested PCM frames or remaining frames
requested_pcm_frames = min(max(pcm_frames, 1),
self.remaining_pcm_frames)
requested_bytes = (self.bytes_per_pcm_frame *
requested_pcm_frames)
pcm_data = self.stream.read_bytes(requested_bytes)
# raise exception if "SSND" chunk exhausted early
if len(pcm_data) < requested_bytes:
from audiotools.text import ERR_AIFF_TRUNCATED_SSND_CHUNK
raise IOError(ERR_AIFF_TRUNCATED_SSND_CHUNK)
else:
self.remaining_pcm_frames -= requested_pcm_frames
# return parsed chunk
return FrameList(pcm_data,
self.channels,
self.bits_per_sample,
True,
True)
def read_closed(self, pcm_frames):
raise ValueError("cannot read closed stream")
def seek(self, pcm_frame_offset):
"""tries to seek to the given PCM frame offset
returns the total amount of frames actually seeked over"""
if pcm_frame_offset < 0:
from audiotools.text import ERR_NEGATIVE_SEEK
raise ValueError(ERR_NEGATIVE_SEEK)
# ensure one doesn't walk off the end of the file
pcm_frame_offset = min(pcm_frame_offset,
self.total_pcm_frames)
# position file in "SSND" chunk
self.stream.setpos(self.ssnd_start)
self.stream.seek((pcm_frame_offset * self.bytes_per_pcm_frame), 1)
self.remaining_pcm_frames = (self.total_pcm_frames -
pcm_frame_offset)
return pcm_frame_offset
def seek_closed(self, pcm_frame_offset):
raise ValueError("cannot seek closed stream")
def close(self):
"""closes the stream for reading"""
self.stream.close()
self.read = self.read_closed
self.seek = self.seek_closed
class SHNDecoder(object):
def __init__(self, filename):
self.reader = BitstreamReader(open(filename, "rb"), False)
(self.file_type,
self.channels,
self.block_length,
self.max_LPC,
self.number_of_means) = self.read_header()
if (1 <= self.file_type) and (self.file_type <= 2):
self.bits_per_sample = 8
self.signed_samples = (self.file_type == 1)
elif (3 <= self.file_type) and (self.file_type <= 6):
self.bits_per_sample = 16
self.signed_samples = (self.file_type in (3, 5))
else:
raise ValueError("unsupported Shorten file type")
self.wrapped_samples = [[0] * 3 for c in range(self.channels)]
self.means = [[0] * self.number_of_means
for c in range(self.channels)]
self.left_shift = 0
self.stream_finished = False
# try to read the first command for a wave/aiff header
data_start = self.reader.getpos()
self.read_metadata()
self.reader.setpos(data_start)
def read_metadata(self):
from io import BytesIO
command = self.unsigned(2)
if command == 9:
# got verbatim, so read data
verbatim_bytes = ints_to_bytes([self.unsigned(8) & 0xFF
for i in range(self.unsigned(5))])
try:
wave = BitstreamReader(BytesIO(verbatim_bytes), True)
header = wave.read_bytes(12)
if header.startswith(b"RIFF") and header.endswith(b"WAVE"):
# got RIFF/WAVE header, so parse wave blocks as needed
total_size = len(verbatim_bytes) - 12
while total_size > 0:
(chunk_id, chunk_size) = wave.parse("4b 32u")
total_size -= 8
if chunk_id == b'fmt ':
(channels,
self.sample_rate,
bits_per_sample,
channel_mask) = parse_fmt(
wave.substream(chunk_size))
self.channel_mask = int(channel_mask)
return
else:
if chunk_size % 2:
wave.read_bytes(chunk_size + 1)
total_size -= (chunk_size + 1)
else:
wave.read_bytes(chunk_size)
total_size -= chunk_size
else:
# no fmt chunk, so use default metadata
pass
except (IOError, ValueError):
pass
try:
aiff = BitstreamReader(BytesIO(verbatim_bytes), False)
header = aiff.read_bytes(12)
if header.startswith(b"FORM") and header.endswith(b"AIFF"):
# got FORM/AIFF header, so parse aiff blocks as needed
total_size = len(verbatim_bytes) - 12
while total_size > 0:
(chunk_id, chunk_size) = aiff.parse("4b 32u")
total_size -= 8
if chunk_id == b'COMM':
(channels,
total_sample_frames,
bits_per_sample,
self.sample_rate,
channel_mask) = parse_comm(
aiff.substream(chunk_size))
self.channel_mask = int(channel_mask)
return
else:
if chunk_size % 2:
aiff.read_bytes(chunk_size + 1)
total_size -= (chunk_size + 1)
else:
aiff.read_bytes(chunk_size)
total_size -= chunk_size
else:
# no COMM chunk, so use default metadata
pass
except IOError:
pass
# got something else, so invent some PCM parameters
self.sample_rate = 44100
if self.channels == 1:
self.channel_mask = 0x4
elif self.channels == 2:
self.channel_mask = 0x3
else:
self.channel_mask = 0
def unsigned(self, c):
MSB = self.reader.unary(1)
LSB = self.reader.read(c)
return MSB * 2 ** c + LSB
def signed(self, c):
u = self.unsigned(c + 1)
if (u % 2) == 0:
return u // 2
else:
return -(u // 2) - 1
def long(self):
return self.unsigned(self.unsigned(2))
def skip_unsigned(self, c):
self.reader.skip_unary(1)
self.reader.skip(c)
def read_header(self):
magic = self.reader.read_bytes(4)
if magic != b"ajkg":
raise ValueError("invalid magic number")
version = self.reader.read(8)
if version != 2:
raise ValueError("unsupported version")
file_type = self.long()
channels = self.long()
block_length = self.long()
max_LPC = self.long()
number_of_means = self.long()
bytes_to_skip = self.long()
self.reader.read_bytes(bytes_to_skip)
return (file_type, channels, block_length, max_LPC, number_of_means)
def read(self, pcm_frames):
if self.stream_finished:
return from_channels([empty_framelist(1, self.bits_per_sample)
for channel in range(self.channels)])
c = 0
samples = []
unshifted = []
while True:
command = self.unsigned(2)
if (((0 <= command) and (command <= 3) or
(7 <= command) and (command <= 8))):
# audio data commands
if command == 0: # DIFF0
samples.append(self.read_diff0(self.block_length,
self.means[c]))
elif command == 1: # DIFF1
samples.append(self.read_diff1(self.block_length,
self.wrapped_samples[c]))
elif command == 2: # DIFF2
samples.append(self.read_diff2(self.block_length,
self.wrapped_samples[c]))
elif command == 3: # DIFF3
samples.append(self.read_diff3(self.block_length,
self.wrapped_samples[c]))
elif command == 7: # QLPC
samples.append(self.read_qlpc(self.block_length,
self.means[c],
self.wrapped_samples[c]))
elif command == 8: # ZERO
samples.append([0] * self.block_length)
# update means for channel
self.means[c].append(shnmean(samples[c]))
self.means[c] = self.means[c][1:]
# wrap samples for next command in channel
self.wrapped_samples[c] = samples[c][-(max(3, self.max_LPC)):]
# apply left shift to samples
if self.left_shift > 0:
unshifted.append([s << self.left_shift
for s in samples[c]])
else:
unshifted.append(samples[c])
c += 1
if c == self.channels:
# return a FrameList from shifted data
return from_channels([from_list(channel, 1,
self.bits_per_sample,
self.signed_samples)
for channel in unshifted])
else:
# non audio commands
if command == 4: # QUIT
self.stream_finished = True
return from_channels(
[empty_framelist(1, self.bits_per_sample)
for channel in range(self.channels)])
elif command == 5: # BLOCKSIZE
self.block_length = self.long()
elif command == 6: # BITSHIFT
self.left_shift = self.unsigned(2)
elif command == 9: # VERBATIM
# skip this command during reading
size = self.unsigned(5)
for i in range(size):
self.skip_unsigned(8)
else:
raise ValueError("unsupported Shorten command")
def read_diff0(self, block_length, means):
offset = shnmean(means)
energy = self.unsigned(3)
samples = []
for i in range(block_length):
residual = self.signed(energy)
samples.append(residual + offset)
return samples
def read_diff1(self, block_length, previous_samples):
samples = previous_samples[-1:]
energy = self.unsigned(3)
for i in range(1, block_length + 1):
residual = self.signed(energy)
samples.append(samples[i - 1] + residual)
return samples[1:]
def read_diff2(self, block_length, previous_samples):
samples = previous_samples[-2:]
energy = self.unsigned(3)
for i in range(2, block_length + 2):
residual = self.signed(energy)
samples.append((2 * samples[i - 1]) - samples[i - 2] + residual)
return samples[2:]
def read_diff3(self, block_length, previous_samples):
samples = previous_samples[-3:]
energy = self.unsigned(3)
for i in range(3, block_length + 3):
residual = self.signed(energy)
samples.append((3 * (samples[i - 1] - samples[i - 2])) +
samples[i - 3] + residual)
return samples[3:]
def read_qlpc(self, block_length, means, previous_samples):
offset = shnmean(means)
energy = self.unsigned(3)
LPC_count = self.unsigned(2)
LPC_coeff = [self.signed(5) for i in range(LPC_count)]
unoffset = []
samples = previous_samples[-LPC_count:]
for i in range(block_length):
residual = self.signed(energy)
LPC_sum = 2 ** 5
for j in range(LPC_count):
if (i - j - 1) < 0:
# apply offset to warm-up samples
LPC_sum += (LPC_coeff[j] *
(samples[LPC_count + (i - j - 1)] - offset))
else:
LPC_sum += LPC_coeff[j] * unoffset[i - j - 1]
unoffset.append(LPC_sum // 2 ** 5 + residual)
return [u + offset for u in unoffset]
def close(self):
self.reader.close()
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, traceback):
self.close()
class SHNDecoder(object):
def __init__(self, filename):
self.reader = BitstreamReader(open(filename, "rb"), False)
(self.file_type, self.channels, self.block_length, self.max_LPC,
self.number_of_means) = self.read_header()
if (1 <= self.file_type) and (self.file_type <= 2):
self.bits_per_sample = 8
self.signed_samples = (self.file_type == 1)
elif (3 <= self.file_type) and (self.file_type <= 6):
self.bits_per_sample = 16
self.signed_samples = (self.file_type in (3, 5))
else:
raise ValueError("unsupported Shorten file type")
self.wrapped_samples = [[0] * 3 for c in range(self.channels)]
self.means = [[0] * self.number_of_means for c in range(self.channels)]
self.left_shift = 0
self.stream_finished = False
# try to read the first command for a wave/aiff header
data_start = self.reader.getpos()
self.read_metadata()
self.reader.setpos(data_start)
def read_metadata(self):
from io import BytesIO
command = self.unsigned(2)
if command == 9:
# got verbatim, so read data
verbatim_bytes = ints_to_bytes(
[self.unsigned(8) & 0xFF for i in range(self.unsigned(5))])
try:
wave = BitstreamReader(BytesIO(verbatim_bytes), True)
header = wave.read_bytes(12)
if header.startswith(b"RIFF") and header.endswith(b"WAVE"):
# got RIFF/WAVE header, so parse wave blocks as needed
total_size = len(verbatim_bytes) - 12
while total_size > 0:
(chunk_id, chunk_size) = wave.parse("4b 32u")
total_size -= 8
if chunk_id == b'fmt ':
(channels, self.sample_rate, bits_per_sample,
channel_mask) = parse_fmt(
wave.substream(chunk_size))
self.channel_mask = int(channel_mask)
return
else:
if chunk_size % 2:
wave.read_bytes(chunk_size + 1)
total_size -= (chunk_size + 1)
else:
wave.read_bytes(chunk_size)
total_size -= chunk_size
else:
# no fmt chunk, so use default metadata
pass
except (IOError, ValueError):
pass
try:
aiff = BitstreamReader(BytesIO(verbatim_bytes), False)
header = aiff.read_bytes(12)
if header.startswith(b"FORM") and header.endswith(b"AIFF"):
# got FORM/AIFF header, so parse aiff blocks as needed
total_size = len(verbatim_bytes) - 12
while total_size > 0:
(chunk_id, chunk_size) = aiff.parse("4b 32u")
total_size -= 8
if chunk_id == b'COMM':
(channels, total_sample_frames, bits_per_sample,
self.sample_rate, channel_mask) = parse_comm(
aiff.substream(chunk_size))
self.channel_mask = int(channel_mask)
return
else:
if chunk_size % 2:
aiff.read_bytes(chunk_size + 1)
total_size -= (chunk_size + 1)
else:
aiff.read_bytes(chunk_size)
total_size -= chunk_size
else:
# no COMM chunk, so use default metadata
pass
except IOError:
pass
# got something else, so invent some PCM parameters
self.sample_rate = 44100
if self.channels == 1:
self.channel_mask = 0x4
elif self.channels == 2:
self.channel_mask = 0x3
else:
self.channel_mask = 0
def unsigned(self, c):
MSB = self.reader.unary(1)
LSB = self.reader.read(c)
return MSB * 2**c + LSB
def signed(self, c):
u = self.unsigned(c + 1)
if (u % 2) == 0:
return u // 2
else:
return -(u // 2) - 1
def long(self):
return self.unsigned(self.unsigned(2))
def skip_unsigned(self, c):
self.reader.skip_unary(1)
self.reader.skip(c)
def read_header(self):
magic = self.reader.read_bytes(4)
if magic != b"ajkg":
raise ValueError("invalid magic number")
version = self.reader.read(8)
if version != 2:
raise ValueError("unsupported version")
file_type = self.long()
channels = self.long()
block_length = self.long()
max_LPC = self.long()
number_of_means = self.long()
bytes_to_skip = self.long()
self.reader.read_bytes(bytes_to_skip)
return (file_type, channels, block_length, max_LPC, number_of_means)
def read(self, pcm_frames):
if self.stream_finished:
return from_channels([
empty_framelist(1, self.bits_per_sample)
for channel in range(self.channels)
])
c = 0
samples = []
unshifted = []
while True:
command = self.unsigned(2)
if (((0 <= command) and (command <= 3)
or (7 <= command) and (command <= 8))):
# audio data commands
if command == 0: # DIFF0
samples.append(
self.read_diff0(self.block_length, self.means[c]))
elif command == 1: # DIFF1
samples.append(
self.read_diff1(self.block_length,
self.wrapped_samples[c]))
elif command == 2: # DIFF2
samples.append(
self.read_diff2(self.block_length,
self.wrapped_samples[c]))
elif command == 3: # DIFF3
samples.append(
self.read_diff3(self.block_length,
self.wrapped_samples[c]))
elif command == 7: # QLPC
samples.append(
self.read_qlpc(self.block_length, self.means[c],
self.wrapped_samples[c]))
elif command == 8: # ZERO
samples.append([0] * self.block_length)
# update means for channel
self.means[c].append(shnmean(samples[c]))
self.means[c] = self.means[c][1:]
# wrap samples for next command in channel
self.wrapped_samples[c] = samples[c][-(max(3, self.max_LPC)):]
# apply left shift to samples
if self.left_shift > 0:
unshifted.append(
[s << self.left_shift for s in samples[c]])
else:
unshifted.append(samples[c])
c += 1
if c == self.channels:
# return a FrameList from shifted data
return from_channels([
from_list(channel, 1, self.bits_per_sample,
self.signed_samples) for channel in unshifted
])
else:
# non audio commands
if command == 4: # QUIT
self.stream_finished = True
return from_channels([
empty_framelist(1, self.bits_per_sample)
for channel in range(self.channels)
])
elif command == 5: # BLOCKSIZE
self.block_length = self.long()
elif command == 6: # BITSHIFT
self.left_shift = self.unsigned(2)
elif command == 9: # VERBATIM
# skip this command during reading
size = self.unsigned(5)
for i in range(size):
self.skip_unsigned(8)
else:
raise ValueError("unsupported Shorten command")
def read_diff0(self, block_length, means):
offset = shnmean(means)
energy = self.unsigned(3)
samples = []
for i in range(block_length):
residual = self.signed(energy)
samples.append(residual + offset)
return samples
def read_diff1(self, block_length, previous_samples):
samples = previous_samples[-1:]
energy = self.unsigned(3)
for i in range(1, block_length + 1):
residual = self.signed(energy)
samples.append(samples[i - 1] + residual)
return samples[1:]
def read_diff2(self, block_length, previous_samples):
samples = previous_samples[-2:]
energy = self.unsigned(3)
for i in range(2, block_length + 2):
residual = self.signed(energy)
samples.append((2 * samples[i - 1]) - samples[i - 2] + residual)
return samples[2:]
def read_diff3(self, block_length, previous_samples):
samples = previous_samples[-3:]
energy = self.unsigned(3)
for i in range(3, block_length + 3):
residual = self.signed(energy)
samples.append((3 * (samples[i - 1] - samples[i - 2])) +
samples[i - 3] + residual)
return samples[3:]
def read_qlpc(self, block_length, means, previous_samples):
offset = shnmean(means)
energy = self.unsigned(3)
LPC_count = self.unsigned(2)
LPC_coeff = [self.signed(5) for i in range(LPC_count)]
unoffset = []
samples = previous_samples[-LPC_count:]
for i in range(block_length):
residual = self.signed(energy)
LPC_sum = 2**5
for j in range(LPC_count):
if (i - j - 1) < 0:
# apply offset to warm-up samples
LPC_sum += (LPC_coeff[j] * (samples[LPC_count +
(i - j - 1)] - offset))
else:
LPC_sum += LPC_coeff[j] * unoffset[i - j - 1]
unoffset.append(LPC_sum // 2**5 + residual)
return [u + offset for u in unoffset]
def close(self):
self.reader.close()
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, traceback):
self.close()
class WavPackDecoder(object):
def __init__(self, filename):
self.reader = BitstreamReader(open(filename, "rb"), True)
stream_start = self.reader.getpos()
# read initial block to populate
# sample_rate, bits_per_sample, channels, and channel_mask
block_header = Block_Header.read(self.reader)
sub_blocks_size = block_header.block_size - 24
sub_blocks_data = self.reader.substream(sub_blocks_size)
if block_header.sample_rate != 15:
self.sample_rate = [6000, 8000, 9600, 11025, 12000,
16000, 22050, 24000, 32000, 44100,
48000, 64000, 88200, 96000,
192000][block_header.sample_rate]
else:
sub_blocks_start = sub_blocks_data.getpos()
try:
for sub_block in sub_blocks(sub_blocks_data,
sub_blocks_size):
if (((sub_block.metadata_function == 7) and
(sub_block.nondecoder_data == 1))):
self.sample_rate = sub_block.data.read(
sub_block.data_size() * 8)
break
else:
raise ValueError("invalid sample rate")
finally:
sub_blocks_data.setpos(sub_blocks_start)
self.bits_per_sample = \
[8, 16, 24, 32][block_header.bits_per_sample]
if block_header.initial_block and block_header.final_block:
if (((block_header.mono_output == 0) or
(block_header.false_stereo == 1))):
self.channels = 2
self.channel_mask = 0x3
else:
self.channels = 1
self.channel_mask = 0x4
else:
# look for channel mask sub block
sub_blocks_start = sub_blocks_data.getpos()
try:
for sub_block in sub_blocks(sub_blocks_data, sub_blocks_size):
if (((sub_block.metadata_function == 13) and
(sub_block.nondecoder_data == 0))):
self.channels = sub_block.data.read(8)
self.channel_mask = sub_block.data.read(
(sub_block.data_size() - 1) * 8)
break
else:
# FIXME - handle case of no channel mask sub block
raise NotImplementedError()
finally:
sub_blocks_data.setpos(sub_blocks_start)
self.reader.setpos(stream_start)
self.pcm_finished = False
self.md5_checked = False
self.md5sum = md5()
def read(self, pcm_frames):
if self.pcm_finished:
if not self.md5_checked:
block_start = self.reader.getpos()
try:
try:
header = Block_Header.read(self.reader)
sub_blocks_size = header.block_size - 24
sub_blocks_data = \
self.reader.substream(sub_blocks_size)
for sub_block in sub_blocks(sub_blocks_data,
sub_blocks_size):
if (((sub_block.metadata_function == 6) and
(sub_block.nondecoder_data == 1))):
if ((sub_block.data.read_bytes(16) !=
self.md5sum.digest())):
raise ValueError("invalid stream MD5 sum")
except (IOError, ValueError):
# no error if a block isn't found
pass
finally:
self.reader.setpos(block_start)
return empty_framelist(self.channels, self.bits_per_sample)
channels = []
while True: # in place of a do-while loop
try:
block_header = Block_Header.read(self.reader)
except (ValueError, IOError):
self.pcm_finished = True
return empty_framelist(self.channels, self.bits_per_sample)
sub_blocks_size = block_header.block_size - 24
sub_blocks_data = self.reader.substream(sub_blocks_size)
channels.extend(read_block(block_header,
sub_blocks_size,
sub_blocks_data))
if block_header.final_block == 1:
break
if ((block_header.block_index +
block_header.block_samples) >= block_header.total_samples):
self.pcm_finished = True
# combine channels of audio data into single block
block = from_channels([from_list(ch, 1, self.bits_per_sample, True)
for ch in channels])
# update MD5 sum
self.md5sum.update(block.to_bytes(False, self.bits_per_sample > 8))
# return single block of audio data
return block
def close(self):
self.reader.close()
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, traceback):
self.close()
class WavPackDecoder(object):
def __init__(self, filename):
self.reader = BitstreamReader(open(filename, "rb"), True)
stream_start = self.reader.getpos()
# read initial block to populate
# sample_rate, bits_per_sample, channels, and channel_mask
block_header = Block_Header.read(self.reader)
sub_blocks_size = block_header.block_size - 24
sub_blocks_data = self.reader.substream(sub_blocks_size)
if block_header.sample_rate != 15:
self.sample_rate = [
6000, 8000, 9600, 11025, 12000, 16000, 22050, 24000, 32000,
44100, 48000, 64000, 88200, 96000, 192000
][block_header.sample_rate]
else:
sub_blocks_start = sub_blocks_data.getpos()
try:
for sub_block in sub_blocks(sub_blocks_data, sub_blocks_size):
if (((sub_block.metadata_function == 7)
and (sub_block.nondecoder_data == 1))):
self.sample_rate = sub_block.data.read(
sub_block.data_size() * 8)
break
else:
raise ValueError("invalid sample rate")
finally:
sub_blocks_data.setpos(sub_blocks_start)
self.bits_per_sample = \
[8, 16, 24, 32][block_header.bits_per_sample]
if block_header.initial_block and block_header.final_block:
if (((block_header.mono_output == 0)
or (block_header.false_stereo == 1))):
self.channels = 2
self.channel_mask = 0x3
else:
self.channels = 1
self.channel_mask = 0x4
else:
# look for channel mask sub block
sub_blocks_start = sub_blocks_data.getpos()
try:
for sub_block in sub_blocks(sub_blocks_data, sub_blocks_size):
if (((sub_block.metadata_function == 13)
and (sub_block.nondecoder_data == 0))):
self.channels = sub_block.data.read(8)
self.channel_mask = sub_block.data.read(
(sub_block.data_size() - 1) * 8)
break
else:
# FIXME - handle case of no channel mask sub block
raise NotImplementedError()
finally:
sub_blocks_data.setpos(sub_blocks_start)
self.reader.setpos(stream_start)
self.pcm_finished = False
self.md5_checked = False
self.md5sum = md5()
def read(self, pcm_frames):
if self.pcm_finished:
if not self.md5_checked:
block_start = self.reader.getpos()
try:
try:
header = Block_Header.read(self.reader)
sub_blocks_size = header.block_size - 24
sub_blocks_data = \
self.reader.substream(sub_blocks_size)
for sub_block in sub_blocks(sub_blocks_data,
sub_blocks_size):
if (((sub_block.metadata_function == 6)
and (sub_block.nondecoder_data == 1))):
if ((sub_block.data.read_bytes(16) !=
self.md5sum.digest())):
raise ValueError("invalid stream MD5 sum")
except (IOError, ValueError):
# no error if a block isn't found
pass
finally:
self.reader.setpos(block_start)
return empty_framelist(self.channels, self.bits_per_sample)
channels = []
while True: # in place of a do-while loop
try:
block_header = Block_Header.read(self.reader)
except (ValueError, IOError):
self.pcm_finished = True
return empty_framelist(self.channels, self.bits_per_sample)
sub_blocks_size = block_header.block_size - 24
sub_blocks_data = self.reader.substream(sub_blocks_size)
channels.extend(
read_block(block_header, sub_blocks_size, sub_blocks_data))
if block_header.final_block == 1:
break
if ((block_header.block_index + block_header.block_samples) >=
block_header.total_samples):
self.pcm_finished = True
# combine channels of audio data into single block
block = from_channels(
[from_list(ch, 1, self.bits_per_sample, True) for ch in channels])
# update MD5 sum
self.md5sum.update(block.to_bytes(False, self.bits_per_sample > 8))
# return single block of audio data
return block
def close(self):
self.reader.close()
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, traceback):
self.close()
class ALACDecoder(object):
def __init__(self, filename):
self.reader = BitstreamReader(open(filename, "rb"), False)
stream_start = self.reader.getpos()
# 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.setpos(stream_start)
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.setpos(stream_start)
(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")
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()
