mutagen/oggvorbis.py

   1 # Ogg Vorbis support.
   2 #
   3 # Copyright 2006 Joe Wreschnig <piman@sacredchao.net>
   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         if nominal_bitrate == 0:
  52             self.bitrate = (max_bitrate + min_bitrate) // 2
  53         elif max_bitrate and max_bitrate < nominal_bitrate:
  54             # If the max bitrate is less than the nominal, we know
  55             # the nominal is wrong.
  56             self.bitrate = max_bitrate
  57         elif min_bitrate > nominal_bitrate:
  58             self.bitrate = min_bitrate
  59         else:
  60             self.bitrate = nominal_bitrate
  61
  62     def pprint(self):
  63         return "Ogg Vorbis, %.2f seconds, %d bps" % (self.length, self.bitrate)
  64
  65 class OggVCommentDict(VCommentDict):
  66     """Vorbis comments embedded in an Ogg bitstream."""
  67
  68     def __init__(self, fileobj, info):
  69         pages = []
  70         complete = False
  71         while not complete:
  72             page = OggPage(fileobj)
  73             if page.serial == info.serial:
  74                 pages.append(page)
  75                 complete = page.complete or (len(page.packets) > 1)
  76         data = OggPage.to_packets(pages)[0][7:] # Strip off "\x03vorbis".
  77         super(OggVCommentDict, self).__init__(data)
  78
  79     def _inject(self, fileobj):
  80         """Write tag data into the Vorbis comment packet/page."""
  81
  82         # Find the old pages in the file; we'll need to remove them,
  83         # plus grab any stray setup packet data out of them.
  84         fileobj.seek(0)
  85         page = OggPage(fileobj)
  86         while not page.packets[0].startswith("\x03vorbis"):
  87             page = OggPage(fileobj)
  88
  89         old_pages = [page]
  90         while not (old_pages[-1].complete or len(old_pages[-1].packets) > 1):
  91             page = OggPage(fileobj)
  92             if page.serial == old_pages[0].serial:
  93                 old_pages.append(page)
  94
  95         packets = OggPage.to_packets(old_pages, strict=False)
  96
  97         # Set the new comment packet.
  98         packets[0] = "\x03vorbis" + self.write()
  99
 100         new_pages = OggPage.from_packets(packets, old_pages[0].sequence)
 101         OggPage.replace(fileobj, old_pages, new_pages)
 102
 103 class OggVorbis(OggFileType):
 104     """An Ogg Vorbis file."""
 105
 106     _Info = OggVorbisInfo
 107     _Tags = OggVCommentDict
 108     _Error = OggVorbisHeaderError
 109     _mimes = ["audio/vorbis", "audio/x-vorbis"]
 110
 111     def score(filename, fileobj, header):
 112         return (header.startswith("OggS") * ("\x01vorbis" in header))
 113     score = staticmethod(score)
 114
 115 Open = OggVorbis
 116
 117 def delete(filename):
 118     """Remove tags from a file."""
 119     OggVorbis(filename).delete()