Initial Commit

lib/mutagen/asf.py

@@ -0,0 +1,862 @@
+# -*- coding: utf-8 -*-
+
+# Copyright (C) 2005-2006  Joe Wreschnig
+# Copyright (C) 2006-2007  Lukas Lalinsky
+
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 as
+# published by the Free Software Foundation.
+
+"""Read and write ASF (Window Media Audio) files."""
+
+__all__ = ["ASF", "Open"]
+
+import sys
+import struct
+from mutagen import FileType, Metadata, StreamInfo
+from mutagen._util import (insert_bytes, delete_bytes, DictMixin,
+                           total_ordering, MutagenError)
+from ._compat import swap_to_string, text_type, PY2, string_types, reraise, \
+    xrange, long_, PY3
+
+
+class error(IOError, MutagenError):
+    pass
+
+
+class ASFError(error):
+    pass
+
+
+class ASFHeaderError(error):
+    pass
+
+
+class ASFInfo(StreamInfo):
+    """ASF stream information."""
+
+    def __init__(self):
+        self.length = 0.0
+        self.sample_rate = 0
+        self.bitrate = 0
+        self.channels = 0
+
+    def pprint(self):
+        s = "Windows Media Audio %d bps, %s Hz, %d channels, %.2f seconds" % (
+            self.bitrate, self.sample_rate, self.channels, self.length)
+        return s
+
+
+class ASFTags(list, DictMixin, Metadata):
+    """Dictionary containing ASF attributes."""
+
+    def pprint(self):
+        return "\n".join("%s=%s" % (k, v) for k, v in self)
+
+    def __getitem__(self, key):
+        """A list of values for the key.
+
+        This is a copy, so comment['title'].append('a title') will not
+        work.
+
+        """
+
+        # PY3 only
+        if isinstance(key, slice):
+            return list.__getitem__(self, key)
+
+        values = [value for (k, value) in self if k == key]
+        if not values:
+            raise KeyError(key)
+        else:
+            return values
+
+    def __delitem__(self, key):
+        """Delete all values associated with the key."""
+
+        # PY3 only
+        if isinstance(key, slice):
+            return list.__delitem__(self, key)
+
+        to_delete = [x for x in self if x[0] == key]
+        if not to_delete:
+            raise KeyError(key)
+        else:
+            for k in to_delete:
+                self.remove(k)
+
+    def __contains__(self, key):
+        """Return true if the key has any values."""
+        for k, value in self:
+            if k == key:
+                return True
+        else:
+            return False
+
+    def __setitem__(self, key, values):
+        """Set a key's value or values.
+
+        Setting a value overwrites all old ones. The value may be a
+        list of Unicode or UTF-8 strings, or a single Unicode or UTF-8
+        string.
+
+        """
+
+        # PY3 only
+        if isinstance(key, slice):
+            return list.__setitem__(self, key, values)
+
+        if not isinstance(values, list):
+            values = [values]
+
+        to_append = []
+        for value in values:
+            if not isinstance(value, ASFBaseAttribute):
+                if isinstance(value, string_types):
+                    value = ASFUnicodeAttribute(value)
+                elif PY3 and isinstance(value, bytes):
+                    value = ASFByteArrayAttribute(value)
+                elif isinstance(value, bool):
+                    value = ASFBoolAttribute(value)
+                elif isinstance(value, int):
+                    value = ASFDWordAttribute(value)
+                elif isinstance(value, long_):
+                    value = ASFQWordAttribute(value)
+                else:
+                    raise TypeError("Invalid type %r" % type(value))
+            to_append.append((key, value))
+
+        try:
+            del(self[key])
+        except KeyError:
+            pass
+
+        self.extend(to_append)
+
+    def keys(self):
+        """Return all keys in the comment."""
+        return self and set(next(iter(zip(*self))))
+
+    def as_dict(self):
+        """Return a copy of the comment data in a real dict."""
+        d = {}
+        for key, value in self:
+            d.setdefault(key, []).append(value)
+        return d
+
+
+class ASFBaseAttribute(object):
+    """Generic attribute."""
+    TYPE = None
+
+    def __init__(self, value=None, data=None, language=None,
+                 stream=None, **kwargs):
+        self.language = language
+        self.stream = stream
+        if data:
+            self.value = self.parse(data, **kwargs)
+        else:
+            if value is None:
+                # we used to support not passing any args and instead assign
+                # them later, keep that working..
+                self.value = None
+            else:
+                self.value = self._validate(value)
+
+    def _validate(self, value):
+        """Raises TypeError or ValueError in case the user supplied value
+        isn't valid.
+        """
+
+        return value
+
+    def data_size(self):
+        raise NotImplementedError
+
+    def __repr__(self):
+        name = "%s(%r" % (type(self).__name__, self.value)
+        if self.language:
+            name += ", language=%d" % self.language
+        if self.stream:
+            name += ", stream=%d" % self.stream
+        name += ")"
+        return name
+
+    def render(self, name):
+        name = name.encode("utf-16-le") + b"\x00\x00"
+        data = self._render()
+        return (struct.pack("<H", len(name)) + name +
+                struct.pack("<HH", self.TYPE, len(data)) + data)
+
+    def render_m(self, name):
+        name = name.encode("utf-16-le") + b"\x00\x00"
+        if self.TYPE == 2:
+            data = self._render(dword=False)
+        else:
+            data = self._render()
+        return (struct.pack("<HHHHI", 0, self.stream or 0, len(name),
+                            self.TYPE, len(data)) + name + data)
+
+    def render_ml(self, name):
+        name = name.encode("utf-16-le") + b"\x00\x00"
+        if self.TYPE == 2:
+            data = self._render(dword=False)
+        else:
+            data = self._render()
+
+        return (struct.pack("<HHHHI", self.language or 0, self.stream or 0,
+                            len(name), self.TYPE, len(data)) + name + data)
+
+
+@swap_to_string
+@total_ordering
+class ASFUnicodeAttribute(ASFBaseAttribute):
+    """Unicode string attribute."""
+    TYPE = 0x0000
+
+    def parse(self, data):
+        try:
+            return data.decode("utf-16-le").strip("\x00")
+        except UnicodeDecodeError as e:
+            reraise(ASFError, e, sys.exc_info()[2])
+
+    def _validate(self, value):
+        if not isinstance(value, text_type):
+            if PY2:
+                return value.decode("utf-8")
+            else:
+                raise TypeError("%r not str" % value)
+        return value
+
+    def _render(self):
+        return self.value.encode("utf-16-le") + b"\x00\x00"
+
+    def data_size(self):
+        return len(self._render())
+
+    def __bytes__(self):
+        return self.value.encode("utf-16-le")
+
+    def __str__(self):
+        return self.value
+
+    def __eq__(self, other):
+        return text_type(self) == other
+
+    def __lt__(self, other):
+        return text_type(self) < other
+
+    __hash__ = ASFBaseAttribute.__hash__
+
+
+@swap_to_string
+@total_ordering
+class ASFByteArrayAttribute(ASFBaseAttribute):
+    """Byte array attribute."""
+    TYPE = 0x0001
+
+    def parse(self, data):
+        assert isinstance(data, bytes)
+        return data
+
+    def _render(self):
+        assert isinstance(self.value, bytes)
+        return self.value
+
+    def _validate(self, value):
+        if not isinstance(value, bytes):
+            raise TypeError("must be bytes/str: %r" % value)
+        return value
+
+    def data_size(self):
+        return len(self.value)
+
+    def __bytes__(self):
+        return self.value
+
+    def __str__(self):
+        return "[binary data (%d bytes)]" % len(self.value)
+
+    def __eq__(self, other):
+        return self.value == other
+
+    def __lt__(self, other):
+        return self.value < other
+
+    __hash__ = ASFBaseAttribute.__hash__
+
+
+@swap_to_string
+@total_ordering
+class ASFBoolAttribute(ASFBaseAttribute):
+    """Bool attribute."""
+    TYPE = 0x0002
+
+    def parse(self, data, dword=True):
+        if dword:
+            return struct.unpack("<I", data)[0] == 1
+        else:
+            return struct.unpack("<H", data)[0] == 1
+
+    def _render(self, dword=True):
+        if dword:
+            return struct.pack("<I", bool(self.value))
+        else:
+            return struct.pack("<H", bool(self.value))
+
+    def _validate(self, value):
+        return bool(value)
+
+    def data_size(self):
+        return 4
+
+    def __bool__(self):
+        return bool(self.value)
+
+    def __bytes__(self):
+        return text_type(self.value).encode('utf-8')
+
+    def __str__(self):
+        return text_type(self.value)
+
+    def __eq__(self, other):
+        return bool(self.value) == other
+
+    def __lt__(self, other):
+        return bool(self.value) < other
+
+    __hash__ = ASFBaseAttribute.__hash__
+
+
+@swap_to_string
+@total_ordering
+class ASFDWordAttribute(ASFBaseAttribute):
+    """DWORD attribute."""
+    TYPE = 0x0003
+
+    def parse(self, data):
+        return struct.unpack("<L", data)[0]
+
+    def _render(self):
+        return struct.pack("<L", self.value)
+
+    def _validate(self, value):
+        value = int(value)
+        if not 0 <= value <= 2 ** 32 - 1:
+            raise ValueError("Out of range")
+        return value
+
+    def data_size(self):
+        return 4
+
+    def __int__(self):
+        return self.value
+
+    def __bytes__(self):
+        return text_type(self.value).encode('utf-8')
+
+    def __str__(self):
+        return text_type(self.value)
+
+    def __eq__(self, other):
+        return int(self.value) == other
+
+    def __lt__(self, other):
+        return int(self.value) < other
+
+    __hash__ = ASFBaseAttribute.__hash__
+
+
+@swap_to_string
+@total_ordering
+class ASFQWordAttribute(ASFBaseAttribute):
+    """QWORD attribute."""
+    TYPE = 0x0004
+
+    def parse(self, data):
+        return struct.unpack("<Q", data)[0]
+
+    def _render(self):
+        return struct.pack("<Q", self.value)
+
+    def _validate(self, value):
+        value = int(value)
+        if not 0 <= value <= 2 ** 64 - 1:
+            raise ValueError("Out of range")
+        return value
+
+    def data_size(self):
+        return 8
+
+    def __int__(self):
+        return self.value
+
+    def __bytes__(self):
+        return text_type(self.value).encode('utf-8')
+
+    def __str__(self):
+        return text_type(self.value)
+
+    def __eq__(self, other):
+        return int(self.value) == other
+
+    def __lt__(self, other):
+        return int(self.value) < other
+
+    __hash__ = ASFBaseAttribute.__hash__
+
+
+@swap_to_string
+@total_ordering
+class ASFWordAttribute(ASFBaseAttribute):
+    """WORD attribute."""
+    TYPE = 0x0005
+
+    def parse(self, data):
+        return struct.unpack("<H", data)[0]
+
+    def _render(self):
+        return struct.pack("<H", self.value)
+
+    def _validate(self, value):
+        value = int(value)
+        if not 0 <= value <= 2 ** 16 - 1:
+            raise ValueError("Out of range")
+        return value
+
+    def data_size(self):
+        return 2
+
+    def __int__(self):
+        return self.value
+
+    def __bytes__(self):
+        return text_type(self.value).encode('utf-8')
+
+    def __str__(self):
+        return text_type(self.value)
+
+    def __eq__(self, other):
+        return int(self.value) == other
+
+    def __lt__(self, other):
+        return int(self.value) < other
+
+    __hash__ = ASFBaseAttribute.__hash__
+
+
+@swap_to_string
+@total_ordering
+class ASFGUIDAttribute(ASFBaseAttribute):
+    """GUID attribute."""
+    TYPE = 0x0006
+
+    def parse(self, data):
+        assert isinstance(data, bytes)
+        return data
+
+    def _render(self):
+        assert isinstance(self.value, bytes)
+        return self.value
+
+    def _validate(self, value):
+        if not isinstance(value, bytes):
+            raise TypeError("must be bytes/str: %r" % value)
+        return value
+
+    def data_size(self):
+        return len(self.value)
+
+    def __bytes__(self):
+        return self.value
+
+    def __str__(self):
+        return repr(self.value)
+
+    def __eq__(self, other):
+        return self.value == other
+
+    def __lt__(self, other):
+        return self.value < other
+
+    __hash__ = ASFBaseAttribute.__hash__
+
+
+UNICODE = ASFUnicodeAttribute.TYPE
+BYTEARRAY = ASFByteArrayAttribute.TYPE
+BOOL = ASFBoolAttribute.TYPE
+DWORD = ASFDWordAttribute.TYPE
+QWORD = ASFQWordAttribute.TYPE
+WORD = ASFWordAttribute.TYPE
+GUID = ASFGUIDAttribute.TYPE
+
+
+def ASFValue(value, kind, **kwargs):
+    try:
+        attr_type = _attribute_types[kind]
+    except KeyError:
+        raise ValueError("Unknown value type %r" % kind)
+    else:
+        return attr_type(value=value, **kwargs)
+
+
+_attribute_types = {
+    ASFUnicodeAttribute.TYPE: ASFUnicodeAttribute,
+    ASFByteArrayAttribute.TYPE: ASFByteArrayAttribute,
+    ASFBoolAttribute.TYPE: ASFBoolAttribute,
+    ASFDWordAttribute.TYPE: ASFDWordAttribute,
+    ASFQWordAttribute.TYPE: ASFQWordAttribute,
+    ASFWordAttribute.TYPE: ASFWordAttribute,
+    ASFGUIDAttribute.TYPE: ASFGUIDAttribute,
+}
+
+
+class BaseObject(object):
+    """Base ASF object."""
+    GUID = None
+
+    def parse(self, asf, data, fileobj, size):
+        self.data = data
+
+    def render(self, asf):
+        data = self.GUID + struct.pack("<Q", len(self.data) + 24) + self.data
+        return data
+
+
+class UnknownObject(BaseObject):
+    """Unknown ASF object."""
+    def __init__(self, guid):
+        assert isinstance(guid, bytes)
+        self.GUID = guid
+
+
+class HeaderObject(object):
+    """ASF header."""
+    GUID = b"\x30\x26\xB2\x75\x8E\x66\xCF\x11\xA6\xD9\x00\xAA\x00\x62\xCE\x6C"
+
+
+class ContentDescriptionObject(BaseObject):
+    """Content description."""
+    GUID = b"\x33\x26\xB2\x75\x8E\x66\xCF\x11\xA6\xD9\x00\xAA\x00\x62\xCE\x6C"
+
+    NAMES = [
+        u"Title",
+        u"Author",
+        u"Copyright",
+        u"Description",
+        u"Rating",
+    ]
+
+    def parse(self, asf, data, fileobj, size):
+        super(ContentDescriptionObject, self).parse(asf, data, fileobj, size)
+        asf.content_description_obj = self
+        lengths = struct.unpack("<HHHHH", data[:10])
+        texts = []
+        pos = 10
+        for length in lengths:
+            end = pos + length
+            if length > 0:
+                texts.append(data[pos:end].decode("utf-16-le").strip(u"\x00"))
+            else:
+                texts.append(None)
+            pos = end
+
+        for key, value in zip(self.NAMES, texts):
+            if value is not None:
+                value = ASFUnicodeAttribute(value=value)
+                asf._tags.setdefault(self.GUID, []).append((key, value))
+
+    def render(self, asf):
+        def render_text(name):
+            value = asf.to_content_description.get(name)
+            if value is not None:
+                return text_type(value).encode("utf-16-le") + b"\x00\x00"
+            else:
+                return b""
+
+        texts = [render_text(x) for x in self.NAMES]
+        data = struct.pack("<HHHHH", *map(len, texts)) + b"".join(texts)
+        return self.GUID + struct.pack("<Q", 24 + len(data)) + data
+
+
+class ExtendedContentDescriptionObject(BaseObject):
+    """Extended content description."""
+    GUID = b"\x40\xA4\xD0\xD2\x07\xE3\xD2\x11\x97\xF0\x00\xA0\xC9\x5E\xA8\x50"
+
+    def parse(self, asf, data, fileobj, size):
+        super(ExtendedContentDescriptionObject, self).parse(
+            asf, data, fileobj, size)
+        asf.extended_content_description_obj = self
+        num_attributes, = struct.unpack("<H", data[0:2])
+        pos = 2
+        for i in xrange(num_attributes):
+            name_length, = struct.unpack("<H", data[pos:pos + 2])
+            pos += 2
+            name = data[pos:pos + name_length]
+            name = name.decode("utf-16-le").strip("\x00")
+            pos += name_length
+            value_type, value_length = struct.unpack("<HH", data[pos:pos + 4])
+            pos += 4
+            value = data[pos:pos + value_length]
+            pos += value_length
+            attr = _attribute_types[value_type](data=value)
+            asf._tags.setdefault(self.GUID, []).append((name, attr))
+
+    def render(self, asf):
+        attrs = asf.to_extended_content_description.items()
+        data = b"".join(attr.render(name) for (name, attr) in attrs)
+        data = struct.pack("<QH", 26 + len(data), len(attrs)) + data
+        return self.GUID + data
+
+
+class FilePropertiesObject(BaseObject):
+    """File properties."""
+    GUID = b"\xA1\xDC\xAB\x8C\x47\xA9\xCF\x11\x8E\xE4\x00\xC0\x0C\x20\x53\x65"
+
+    def parse(self, asf, data, fileobj, size):
+        super(FilePropertiesObject, self).parse(asf, data, fileobj, size)
+        length, _, preroll = struct.unpack("<QQQ", data[40:64])
+        asf.info.length = (length / 10000000.0) - (preroll / 1000.0)
+
+
+class StreamPropertiesObject(BaseObject):
+    """Stream properties."""
+    GUID = b"\x91\x07\xDC\xB7\xB7\xA9\xCF\x11\x8E\xE6\x00\xC0\x0C\x20\x53\x65"
+
+    def parse(self, asf, data, fileobj, size):
+        super(StreamPropertiesObject, self).parse(asf, data, fileobj, size)
+        channels, sample_rate, bitrate = struct.unpack("<HII", data[56:66])
+        asf.info.channels = channels
+        asf.info.sample_rate = sample_rate
+        asf.info.bitrate = bitrate * 8
+
+
+class HeaderExtensionObject(BaseObject):
+    """Header extension."""
+    GUID = b"\xb5\x03\xbf_.\xa9\xcf\x11\x8e\xe3\x00\xc0\x0c Se"
+
+    def parse(self, asf, data, fileobj, size):
+        super(HeaderExtensionObject, self).parse(asf, data, fileobj, size)
+        asf.header_extension_obj = self
+        datasize, = struct.unpack("<I", data[18:22])
+        datapos = 0
+        self.objects = []
+        while datapos < datasize:
+            guid, size = struct.unpack(
+                "<16sQ", data[22 + datapos:22 + datapos + 24])
+            if guid in _object_types:
+                obj = _object_types[guid]()
+            else:
+                obj = UnknownObject(guid)
+            obj.parse(asf, data[22 + datapos + 24:22 + datapos + size],
+                      fileobj, size)
+            self.objects.append(obj)
+            datapos += size
+
+    def render(self, asf):
+        data = b"".join(obj.render(asf) for obj in self.objects)
+        return (self.GUID + struct.pack("<Q", 24 + 16 + 6 + len(data)) +
+                b"\x11\xD2\xD3\xAB\xBA\xA9\xcf\x11" +
+                b"\x8E\xE6\x00\xC0\x0C\x20\x53\x65" +
+                b"\x06\x00" + struct.pack("<I", len(data)) + data)
+
+
+class MetadataObject(BaseObject):
+    """Metadata description."""
+    GUID = b"\xea\xcb\xf8\xc5\xaf[wH\x84g\xaa\x8cD\xfaL\xca"
+
+    def parse(self, asf, data, fileobj, size):
+        super(MetadataObject, self).parse(asf, data, fileobj, size)
+        asf.metadata_obj = self
+        num_attributes, = struct.unpack("<H", data[0:2])
+        pos = 2
+        for i in xrange(num_attributes):
+            (reserved, stream, name_length, value_type,
+             value_length) = struct.unpack("<HHHHI", data[pos:pos + 12])
+            pos += 12
+            name = data[pos:pos + name_length]
+            name = name.decode("utf-16-le").strip("\x00")
+            pos += name_length
+            value = data[pos:pos + value_length]
+            pos += value_length
+            args = {'data': value, 'stream': stream}
+            if value_type == 2:
+                args['dword'] = False
+            attr = _attribute_types[value_type](**args)
+            asf._tags.setdefault(self.GUID, []).append((name, attr))
+
+    def render(self, asf):
+        attrs = asf.to_metadata.items()
+        data = b"".join([attr.render_m(name) for (name, attr) in attrs])
+        return (self.GUID + struct.pack("<QH", 26 + len(data), len(attrs)) +
+                data)
+
+
+class MetadataLibraryObject(BaseObject):
+    """Metadata library description."""
+    GUID = b"\x94\x1c#D\x98\x94\xd1I\xa1A\x1d\x13NEpT"
+
+    def parse(self, asf, data, fileobj, size):
+        super(MetadataLibraryObject, self).parse(asf, data, fileobj, size)
+        asf.metadata_library_obj = self
+        num_attributes, = struct.unpack("<H", data[0:2])
+        pos = 2
+        for i in xrange(num_attributes):
+            (language, stream, name_length, value_type,
+             value_length) = struct.unpack("<HHHHI", data[pos:pos + 12])
+            pos += 12
+            name = data[pos:pos + name_length]
+            name = name.decode("utf-16-le").strip("\x00")
+            pos += name_length
+            value = data[pos:pos + value_length]
+            pos += value_length
+            args = {'data': value, 'language': language, 'stream': stream}
+            if value_type == 2:
+                args['dword'] = False
+            attr = _attribute_types[value_type](**args)
+            asf._tags.setdefault(self.GUID, []).append((name, attr))
+
+    def render(self, asf):
+        attrs = asf.to_metadata_library
+        data = b"".join([attr.render_ml(name) for (name, attr) in attrs])
+        return (self.GUID + struct.pack("<QH", 26 + len(data), len(attrs)) +
+                data)
+
+
+_object_types = {
+    ExtendedContentDescriptionObject.GUID: ExtendedContentDescriptionObject,
+    ContentDescriptionObject.GUID: ContentDescriptionObject,
+    FilePropertiesObject.GUID: FilePropertiesObject,
+    StreamPropertiesObject.GUID: StreamPropertiesObject,
+    HeaderExtensionObject.GUID: HeaderExtensionObject,
+    MetadataLibraryObject.GUID: MetadataLibraryObject,
+    MetadataObject.GUID: MetadataObject,
+}
+
+
+class ASF(FileType):
+    """An ASF file, probably containing WMA or WMV."""
+
+    _mimes = ["audio/x-ms-wma", "audio/x-ms-wmv", "video/x-ms-asf",
+              "audio/x-wma", "video/x-wmv"]
+
+    def load(self, filename):
+        self.filename = filename
+        with open(filename, "rb") as fileobj:
+            self.size = 0
+            self.size1 = 0
+            self.size2 = 0
+            self.offset1 = 0
+            self.offset2 = 0
+            self.num_objects = 0
+            self.info = ASFInfo()
+            self.tags = ASFTags()
+            self.__read_file(fileobj)
+
+    def save(self):
+        # Move attributes to the right objects
+        self.to_content_description = {}
+        self.to_extended_content_description = {}
+        self.to_metadata = {}
+        self.to_metadata_library = []
+        for name, value in self.tags:
+            library_only = (value.data_size() > 0xFFFF or value.TYPE == GUID)
+            can_cont_desc = value.TYPE == UNICODE
+
+            if library_only or value.language is not None:
+                self.to_metadata_library.append((name, value))
+            elif value.stream is not None:
+                if name not in self.to_metadata:
+                    self.to_metadata[name] = value
+                else:
+                    self.to_metadata_library.append((name, value))
+            elif name in ContentDescriptionObject.NAMES:
+                if name not in self.to_content_description and can_cont_desc:
+                    self.to_content_description[name] = value
+                else:
+                    self.to_metadata_library.append((name, value))
+            else:
+                if name not in self.to_extended_content_description:
+                    self.to_extended_content_description[name] = value
+                else:
+                    self.to_metadata_library.append((name, value))
+
+        # Add missing objects
+        if not self.content_description_obj:
+            self.content_description_obj = \
+                ContentDescriptionObject()
+            self.objects.append(self.content_description_obj)
+        if not self.extended_content_description_obj:
+            self.extended_content_description_obj = \
+                ExtendedContentDescriptionObject()
+            self.objects.append(self.extended_content_description_obj)
+        if not self.header_extension_obj:
+            self.header_extension_obj = \
+                HeaderExtensionObject()
+            self.objects.append(self.header_extension_obj)
+        if not self.metadata_obj:
+            self.metadata_obj = \
+                MetadataObject()
+            self.header_extension_obj.objects.append(self.metadata_obj)
+        if not self.metadata_library_obj:
+            self.metadata_library_obj = \
+                MetadataLibraryObject()
+            self.header_extension_obj.objects.append(self.metadata_library_obj)
+
+        # Render the header
+        data = b"".join([obj.render(self) for obj in self.objects])
+        data = (HeaderObject.GUID +
+                struct.pack("<QL", len(data) + 30, len(self.objects)) +
+                b"\x01\x02" + data)
+
+        with open(self.filename, "rb+") as fileobj:
+            size = len(data)
+            if size > self.size:
+                insert_bytes(fileobj, size - self.size, self.size)
+            if size < self.size:
+                delete_bytes(fileobj, self.size - size, 0)
+            fileobj.seek(0)
+            fileobj.write(data)
+
+        self.size = size
+        self.num_objects = len(self.objects)
+
+    def __read_file(self, fileobj):
+        header = fileobj.read(30)
+        if len(header) != 30 or header[:16] != HeaderObject.GUID:
+            raise ASFHeaderError("Not an ASF file.")
+
+        self.extended_content_description_obj = None
+        self.content_description_obj = None
+        self.header_extension_obj = None
+        self.metadata_obj = None
+        self.metadata_library_obj = None
+
+        self.size, self.num_objects = struct.unpack("<QL", header[16:28])
+        self.objects = []
+        self._tags = {}
+        for i in xrange(self.num_objects):
+            self.__read_object(fileobj)
+
+        for guid in [ContentDescriptionObject.GUID,
+                ExtendedContentDescriptionObject.GUID, MetadataObject.GUID,
+                MetadataLibraryObject.GUID]:
+            self.tags.extend(self._tags.pop(guid, []))
+        assert not self._tags
+
+    def __read_object(self, fileobj):
+        guid, size = struct.unpack("<16sQ", fileobj.read(24))
+        if guid in _object_types:
+            obj = _object_types[guid]()
+        else:
+            obj = UnknownObject(guid)
+        data = fileobj.read(size - 24)
+        obj.parse(self, data, fileobj, size)
+        self.objects.append(obj)
+
+    @staticmethod
+    def score(filename, fileobj, header):
+        return header.startswith(HeaderObject.GUID) * 2
+
+Open = ASF