mutagen/musepack.py

   1 # A Musepack reader/tagger
   2 #
   3 # Copyright 2006 Lukas Lalinsky <lalinsky@gmail.com>
   4 #
   5 # This program is free software; you can redistribute it and/or modify
   6 # it under the terms of the GNU General Public License version 2 as
   7 # published by the Free Software Foundation.
   8 #
   9 # $Id: musepack.py 4013 2007-04-23 09:18:22Z luks $
  10
  11 """Musepack audio streams with APEv2 tags.
  12
  13 Musepack is an audio format originally based on the MPEG-1 Layer-2
  14 algorithms. Stream versions 4 through 7 are supported.
  15
  16 For more information, see http://www.musepack.net/.
  17 """
  18
  19 __all__ = ["Musepack", "Open", "delete"]
  20
  21 import struct
  22
  23 from mutagen.apev2 import APEv2File, error, delete
  24 from mutagen.id3 import BitPaddedInt
  25 from mutagen._util import cdata
  26
  27 class MusepackHeaderError(error): pass
  28
  29 RATES = [44100, 48000, 37800, 32000]
  30
  31 class MusepackInfo(object):
  32     """Musepack stream information.
  33
  34     Attributes:
  35     channels -- number of audio channels
  36     length -- file length in seconds, as a float
  37     sample_rate -- audio sampling rate in Hz
  38     bitrate -- audio bitrate, in bits per second
  39     version -- Musepack stream version
  40
  41     Optional Attributes:
  42     title_gain, title_peak -- Replay Gain and peak data for this song
  43     album_gain, album_peak -- Replay Gain and peak data for this album
  44
  45     These attributes are only available in stream version 7. The
  46     gains are a float, +/- some dB. The peaks are a percentage [0..1] of
  47     the maximum amplitude. This means to get a number comparable to
  48     VorbisGain, you must multiply the peak by 2.
  49     """
  50
  51     def __init__(self, fileobj):
  52         header = fileobj.read(32)
  53         if len(header) != 32:
  54             raise MusepackHeaderError("not a Musepack file")
  55         # Skip ID3v2 tags
  56         if header[:3] == "ID3":
  57             size = 10 + BitPaddedInt(header[6:10])
  58             fileobj.seek(size)
  59             header = fileobj.read(32)
  60             if len(header) != 32:
  61                 raise MusepackHeaderError("not a Musepack file")
  62         # SV7
  63         if header.startswith("MP+"):
  64             self.version = ord(header[3]) & 0xF
  65             if self.version < 7:
  66                 raise MusepackHeaderError("not a Musepack file")
  67             frames = cdata.uint_le(header[4:8])
  68             flags = cdata.uint_le(header[8:12])
  69
  70             self.title_peak, self.title_gain = struct.unpack(
  71                 "<Hh", header[12:16])
  72             self.album_peak, self.album_gain = struct.unpack(
  73                 "<Hh", header[16:20])
  74             self.title_gain /= 100.0
  75             self.album_gain /= 100.0
  76             self.title_peak /= 65535.0
  77             self.album_peak /= 65535.0
  78
  79             self.sample_rate = RATES[(flags >> 16) & 0x0003]
  80             self.bitrate = 0
  81         # SV4-SV6
  82         else:
  83             header_dword = cdata.uint_le(header[0:4])
  84             self.version = (header_dword >> 11) & 0x03FF;
  85             if self.version < 4 or self.version > 6:
  86                 raise MusepackHeaderError("not a Musepack file")
  87             self.bitrate = (header_dword >> 23) & 0x01FF;
  88             self.sample_rate = 44100
  89             if self.version >= 5:
  90                 frames = cdata.uint_le(header[4:8])
  91             else:
  92                 frames = cdata.ushort_le(header[6:8])
  93             if self.version < 6:
  94                 frames -= 1
  95         self.channels = 2
  96         self.length = float(frames * 1152 - 576) / self.sample_rate
  97         if not self.bitrate and self.length != 0:
  98             fileobj.seek(0, 2)
  99             self.bitrate = int(fileobj.tell() * 8 / (self.length * 1000) + 0.5)
 100
 101     def pprint(self):
 102         if self.version >= 7:
 103             rg_data = ", Gain: %+0.2f (title), %+0.2f (album)" %(
 104                 self.title_gain, self.album_gain)
 105         else:
 106             rg_data = ""
 107         return "Musepack, %.2f seconds, %d Hz%s" % (
 108             self.length, self.sample_rate, rg_data)
 109
 110 class Musepack(APEv2File):
 111     _Info = MusepackInfo
 112     _mimes = ["audio/x-musepack", "audio/x-mpc"]
 113
 114     def score(filename, fileobj, header):
 115         return header.startswith("MP+") + filename.endswith(".mpc")
 116     score = staticmethod(score)
 117
 118 Open = Musepack