mutagen/oggvorbis.py

   1 # Ogg Vorbis support.
   2 #
   3 # Copyright 2006 Joe Wreschnig
   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: oggvorbis.py 3976 2007-01-13 22:00:14Z piman $
  10
  11 """Read and write Ogg Vorbis comments.
  12
  13 This module handles Vorbis files wrapped in an Ogg bitstream. The
  14 first Vorbis stream found is used.
  15
  16 Read more about Ogg Vorbis at http://vorbis.com/. This module is based
  17 on the specification at http://www.xiph.org/vorbis/doc/Vorbis_I_spec.html.
  18 """
  19
  20 __all__ = ["OggVorbis", "Open", "delete"]
  21
  22 import struct
  23
  24 from mutagen._vorbis import VCommentDict
  25 from mutagen.ogg import OggPage, OggFileType, error as OggError
  26
  27 class error(OggError): pass
  28 class OggVorbisHeaderError(error): pass
  29
  30 class OggVorbisInfo(object):
  31     """Ogg Vorbis stream information.
  32
  33     Attributes:
  34     length - file length in seconds, as a float
  35     bitrate - nominal ('average') bitrate in bits per second, as an int
  36     """
  37
  38     length = 0
  39
  40     def __init__(self, fileobj):
  41         page = OggPage(fileobj)
  42         while not page.packets[0].startswith("\x01vorbis"):
  43             page = OggPage(fileobj)
  44         if not page.first:
  45             raise OggVorbisHeaderError(
  46                 "page has ID header, but doesn't start a stream")
  47         (self.channels, self.sample_rate, max_bitrate, nominal_bitrate,
  48          min_bitrate) = struct.unpack("<B4i", page.packets[0][11:28])
  49         self.serial = page.serial
  50
  51         max_bitrate = max(0, max_bitrate)
  52         min_bitrate = max(0, min_bitrate)
  53         nominal_bitrate = max(0, nominal_bitrate)
  54
  55         if nominal_bitrate == 0:
  56             self.bitrate = (max_bitrate + min_bitrate) // 2
  57         elif max_bitrate and max_bitrate < nominal_bitrate:
  58             # If the max bitrate is less than the nominal, we know
  59             # the nominal is wrong.
  60             self.bitrate = max_bitrate
  61         elif min_bitrate > nominal_bitrate:
  62             self.bitrate = min_bitrate
  63         else:
  64             self.bitrate = nominal_bitrate
  65
  66         if self.bitrate == 0 and self.length > 0:
  67             fileobj.seek(0, 2)
  68             self.bitrate = int((fileobj.tell() * 8) / self.length)
  69
  70
  71     def pprint(self):
  72         return "Ogg Vorbis, %.2f seconds, %d bps" % (self.length, self.bitrate)
  73
  74 class OggVCommentDict(VCommentDict):
  75     """Vorbis comments embedded in an Ogg bitstream."""
  76
  77     def __init__(self, fileobj, info):
  78         pages = []
  79         complete = False
  80         while not complete:
  81             page = OggPage(fileobj)
  82             if page.serial == info.serial:
  83                 pages.append(page)
  84                 complete = page.complete or (len(page.packets) > 1)
  85         data = OggPage.to_packets(pages)[0][7:] # Strip off "\x03vorbis".
  86         super(OggVCommentDict, self).__init__(data)
  87
  88     def _inject(self, fileobj):
  89         """Write tag data into the Vorbis comment packet/page."""
  90
  91         # Find the old pages in the file; we'll need to remove them,
  92         # plus grab any stray setup packet data out of them.
  93         fileobj.seek(0)
  94         page = OggPage(fileobj)
  95         while not page.packets[0].startswith("\x03vorbis"):
  96             page = OggPage(fileobj)
  97
  98         old_pages = [page]
  99         while not (old_pages[-1].complete or len(old_pages[-1].packets) > 1):
 100             page = OggPage(fileobj)
 101             if page.serial == old_pages[0].serial:
 102                 old_pages.append(page)
 103
 104         packets = OggPage.to_packets(old_pages, strict=False)
 105
 106         # Set the new comment packet.
 107         packets[0] = "\x03vorbis" + self.write()
 108
 109         new_pages = OggPage.from_packets(packets, old_pages[0].sequence)
 110         OggPage.replace(fileobj, old_pages, new_pages)
 111
 112 class OggVorbis(OggFileType):
 113     """An Ogg Vorbis file."""
 114
 115     _Info = OggVorbisInfo
 116     _Tags = OggVCommentDict
 117     _Error = OggVorbisHeaderError
 118     _mimes = ["audio/vorbis", "audio/x-vorbis"]
 119
 120     def score(filename, fileobj, header):
 121         return (header.startswith("OggS") * ("\x01vorbis" in header))
 122     score = staticmethod(score)
 123
 124 Open = OggVorbis
 125
 126 def delete(filename):
 127     """Remove tags from a file."""
 128     OggVorbis(filename).delete()