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#!/usr/bin/env python2
#
# Analyse an mp2 file for debugging
#
# The MIT License (MIT)
#
# Copyright (c) 2016 Matthias P. Braendli
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
from pprint import pprint
import sys
import struct
# Header:
# AAAAAAAA AAABBCCD EEEEFFGH IIJJKLMM
# see http://mpgedit.org/mpgedit/mpeg_format/mpeghdr.htm
audio_version_ids = ["MPEG version 2.5", "reserved", "MPEG Version 2 (ISO/IEC 13818-3)", "MPEG Version 1 (ISO/IEC 11172-3)"]
layer_descriptions = ["reserved", "Layer III", "Layer II", "Layer I"]
# bitrate index:
# bits V1,L1 V1,L2 V1,L3 V2,L1 V2, L2 & L3
# 0000 free free free free free
# 0001 32 32 32 32 8
# 0010 64 48 40 48 16
# 0011 96 56 48 56 24
# 0100 128 64 56 64 32
# 0101 160 80 64 80 40
# 0110 192 96 80 96 48
# 0111 224 112 96 112 56
# 1000 256 128 112 128 64
# 1001 288 160 128 144 80
# 1010 320 192 160 160 96
# 1011 352 224 192 176 112
# 1100 384 256 224 192 128
# 1101 416 320 256 224 144
# 1110 448 384 320 256 160
# 1111 bad bad bad bad bad
ver1_layer2_bitrates = [0,
32, 48, 56, 64, 80, 96, 112, 128,
160, 192, 224, 256, 320, 384, -1]
fd = open(sys.argv[1], "rb")
while fd:
headerdata = struct.unpack("!BBBB", fd.read(4))
sync = (headerdata[0] << 3) | (headerdata[1] >> 5)
print("Sync: {:x}".format(sync))
audio_version_id = (headerdata[1] >> 3) & 0x3
print("audio_version_id {}".format(audio_version_ids[audio_version_id]))
layer_description = (headerdata[1] >> 1) & 0x3
print("layer_description {}".format(layer_descriptions[layer_description]))
protection_bit = headerdata[1] & 0x1
if protection_bit:
print("Without protection")
else:
print("With protection")
bitrate_index = headerdata[2] >> 4
print("bitrate_index {}".format(bitrate_index))
sampling_rate = (headerdata[2] >> 2) & 0x3
print("sampling_rate {}".format(sampling_rate))
padding_bit = (headerdata[2] >> 1) & 0x1
if padding_bit:
print("With padding")
else:
print("Without padding")
private_bit = headerdata[2] & 0x1
if private_bit:
print("Private bit set")
else:
print("Private bit unset")
channel_mode = headerdata[3] >> 6
print("channel_mode {}".format(channel_mode))
mode_extension = (headerdata[3] >> 4) & 0x3
print("mode_extension {}".format(mode_extension))
copyright = (headerdata[3] >> 3) & 0x1
if copyright:
print("With copyright")
else:
print("Without copyright")
original = (headerdata[3] >> 2) & 0x1
if original:
print("With original")
else:
print("Without original")
emphasis = headerdata[3] & 0x3
print("emphasis {}".format(emphasis))
if "MPEG Version 1" in audio_version_ids[audio_version_id] and \
layer_descriptions[layer_description] == "Layer II" and \
sampling_rate == 1:
BitRate = ver1_layer2_bitrates[bitrate_index] * 1000
print("bitrate {}".format(BitRate))
SampleRate = 48000
FrameLengthInBytes = 144 * BitRate / SampleRate + padding_bit
print("Frame size {}".format(FrameLengthInBytes))
databytes = fd.read(FrameLengthInBytes - 4)
pprint(["{:02x}".format(ord(d)) for d in databytes[-10:]])
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