mutagen/oggflac.py

   1 # Ogg FLAC 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: oggflac.py 3976 2007-01-13 22:00:14Z piman $
  10
  11 """Read and write Ogg FLAC comments.
  12
  13 This module handles FLAC files wrapped in an Ogg bitstream. The first
  14 FLAC stream found is used. For 'naked' FLACs, see mutagen.flac.
  15
  16 This module is based off the specification at
  17 http://flac.sourceforge.net/ogg_mapping.html.
  18 """
  19
  20 __all__ = ["OggFLAC", "Open", "delete"]
  21
  22 import struct
  23
  24 from cStringIO import StringIO
  25
  26 from mutagen.flac import StreamInfo, VCFLACDict
  27 from mutagen.ogg import OggPage, OggFileType, error as OggError
  28
  29 class error(OggError): pass
  30 class OggFLACHeaderError(error): pass
  31
  32 class OggFLACStreamInfo(StreamInfo):
  33     """Ogg FLAC general header and stream info.
  34
  35     This encompasses the Ogg wrapper for the FLAC STREAMINFO metadata
  36     block, as well as the Ogg codec setup that precedes it.
  37
  38     Attributes (in addition to StreamInfo's):
  39     packets -- number of metadata packets
  40     serial -- Ogg logical stream serial number
  41     """
  42
  43     packets = 0
  44     serial = 0
  45
  46     def load(self, data):
  47         page = OggPage(data)
  48         while not page.packets[0].startswith("\x7FFLAC"):
  49             page = OggPage(data)
  50         major, minor, self.packets, flac = struct.unpack(
  51             ">BBH4s", page.packets[0][5:13])
  52         if flac != "fLaC":
  53             raise OggFLACHeaderError("invalid FLAC marker (%r)" % flac)
  54         elif (major, minor) != (1, 0):
  55             raise OggFLACHeaderError(
  56                 "unknown mapping version: %d.%d" % (major, minor))
  57         self.serial = page.serial
  58
  59         # Skip over the block header.
  60         stringobj = StringIO(page.packets[0][17:])
  61         super(OggFLACStreamInfo, self).load(StringIO(page.packets[0][17:]))
  62
  63     def pprint(self):
  64         return "Ogg " + super(OggFLACStreamInfo, self).pprint()
  65
  66 class OggFLACVComment(VCFLACDict):
  67     def load(self, data, info, errors='replace'):
  68         # data should be pointing at the start of an Ogg page, after
  69         # the first FLAC page.
  70         pages = []
  71         complete = False
  72         while not complete:
  73             page = OggPage(data)
  74             if page.serial == info.serial:
  75                 pages.append(page)
  76                 complete = page.complete or (len(page.packets) > 1)
  77         comment = StringIO(OggPage.to_packets(pages)[0][4:])
  78         super(OggFLACVComment, self).load(comment, errors=errors)
  79
  80     def _inject(self, fileobj):
  81         """Write tag data into the FLAC Vorbis comment packet/page."""
  82
  83         # Ogg FLAC has no convenient data marker like Vorbis, but the
  84         # second packet - and second page - must be the comment data.
  85         fileobj.seek(0)
  86         page = OggPage(fileobj)
  87         while not page.packets[0].startswith("\x7FFLAC"):
  88             page = OggPage(fileobj)
  89
  90         first_page = page
  91         while not (page.sequence == 1 and page.serial == first_page.serial):
  92             page = OggPage(fileobj)
  93
  94         old_pages = [page]
  95         while not (old_pages[-1].complete or len(old_pages[-1].packets) > 1):
  96             page = OggPage(fileobj)
  97             if page.serial == first_page.serial:
  98                 old_pages.append(page)
  99
 100         packets = OggPage.to_packets(old_pages, strict=False)
 101
 102         # Set the new comment block.
 103         data = self.write()
 104         data = packets[0][0] + struct.pack(">I", len(data))[-3:] + data
 105         packets[0] = data
 106
 107         new_pages = OggPage.from_packets(packets, old_pages[0].sequence)
 108         OggPage.replace(fileobj, old_pages, new_pages)
 109
 110 class OggFLAC(OggFileType):
 111     """An Ogg FLAC file."""
 112
 113     _Info = OggFLACStreamInfo
 114     _Tags = OggFLACVComment
 115     _Error = OggFLACHeaderError
 116     _mimes = ["audio/x-oggflac"]
 117
 118     def score(filename, fileobj, header):
 119         return (header.startswith("OggS") * (
 120             ("FLAC" in header) + ("fLaC" in header)))
 121     score = staticmethod(score)
 122
 123 Open = OggFLAC
 124
 125 def delete(filename):
 126     """Remove tags from a file."""
 127     OggFLAC(filename).delete()