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Codec.cs

//
// Codec.cs:
//
// Author:
//   Brian Nickel (brian.nickel@gmail.com)
//
// Copyright (C) 2007 Brian Nickel
//
// This library is free software; you can redistribute it and/or modify
// it  under the terms of the GNU Lesser General Public License version
// 2.1 as published by the Free Software Foundation.
//
// This library is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307
// USA
//

using System;
using System.Collections.Generic;

namespace TagLib.Ogg
{
      /// <summary>
      ///    This abstract class implements <see cref="ICodec" /> to provide
      ///    support for processing packets from an Ogg logical bitstream.
      /// </summary>
      /// <remarks>
      ///    Unsupported Ogg codecs can be added by creating child classes and
      ///    registering them using <see cref="AddCodecProvider" />.
      /// </remarks>
      /// <seealso cref="CodecProvider" />
      /// <seealso cref="AddCodecProvider" />
00039       public abstract class Codec : ICodec
      {
#region Public Delegates
            
            /// <summary>
            ///    Represents a method capable of checking an Ogg header
            ///    packet to see it is matches a given codec.
            /// </summary>
            /// <param name="packet">
            ///    A <see cref="ByteVector" /> object containing an Ogg
            ///    header packet.
            /// </param>
            /// <returns>
            ///    A <see cref="Codec" /> object capable of processing the
            ///    stream from which the packet was generated; otherwise
            ///    <see langword="null" />.
            /// </returns>
            /// <remarks>
            ///    <para>In order to add support for a new Ogg codec in
            ///    TagLib#, a derivative class of <see cref="Codec" /> needs
            ///    to be created. The class then needs to be added to the
            ///    codec detection system by creating a <see
            ///    cref="CodecProvider" /> and registering it with <see
            ///    cref="AddCodecProvider"/>.</para>
            ///    <para>A method implementing <see cref="CodecProvider" />
            ///    should read <paramref name="packet" /> to determine if
            ///    it's subclass can handle the data. If it can, it should
            ///    return a new instance of that class, but in no way act
            ///    upon the data. If the class cannot be used to read the
            ///    packet, <see langref="null" /> indicates to the system
            ///    that it needs to try anther codec provider.</para>
            /// </remarks>
            /// <example>
            ///    <para>The following example would check for a Speex
            ///    packet and return a Speex codec:</para>
            ///    <code lang="C++">
            /// Codec.AddCodecProvider (delegate (ByteVector packet) {
            ///   return packet.StartsWith ("Speex   ") ? new MySpeexCodec () : null;
            /// });
            ///    </code>
            /// </example>
            public delegate Codec CodecProvider (ByteVector packet);
            
#endregion
            
            
            
#region Private Static Fields
            
            /// <summary>
            ///    Contains registered codec providers.
            /// </summary>
00091             private static List<CodecProvider> providers =
                  new List<CodecProvider> ();
            
#endregion
            
            
            
#region Private Static Methods
            
            /// <summary>
            ///    Determines the correct codec to use for a stream header
            ///    packet.
            /// </summary>
            /// <param name="packet">
            ///    A <see cref="ByteVector" /> object containing the first
            ///    packet of an Ogg logical bitstream.
            /// </param>
            /// <returns>
            ///    A <see cref="Codec" /> object capable of handling
            ///    <paramref name="packet" /> and subsequent packets from
            ///    the same stream.
            /// </returns>
            /// <exception cref="UnsupportedFormatException">
            ///    No registered codec capable of processing <paramref
            ///    name="packet" /> could be found.
            /// </exception>
            /// <remarks>
            ///    This method will first use <see cref="CodecProvider" />
            ///    delegates registered with <see cref="AddCodecProvider" />
            ///    and then attempt to use the built-in codecs.
            /// </remarks>
00122             public static Codec GetCodec (ByteVector packet)
            {
                  Codec c = null;
                  
                  foreach (CodecProvider p in providers) {
                        c = p (packet);
                        if (c != null) return c;
                  }
                  
                  c = Codecs.Vorbis.FromPacket (packet);
                  if (c != null)
                        return c;
                  
                  c = Codecs.Theora.FromPacket (packet);
                  if (c != null)
                        return c;
                  
                  throw new UnsupportedFormatException ("Unknown codec.");
            }
            
            /// <summary>
            ///    Adds a codec 
            /// </summary>
            /// <param name="provider">
            /// A <see cref="CodecProvider"/>
            /// </param>
            /// <remarks>
            ///    A <see cref="CodecProvider" /> delegate is used to add
            ///    support for new <see cref="Codec" /> subclasses in <see
            ///    cref="GetCodec" />.
            /// </remarks>
            /// <seealso cref="CodecProvider" />
00154             public static void AddCodecProvider (CodecProvider provider)
            {
                  providers.Insert (0, provider);
            }
            
#endregion
            
            
            
#region Private Properties
            
            /// <summary>
            ///    Gets a text description of the media represented by the
            ///    current instance.
            /// </summary>
            /// <value>
            ///    A <see cref="string" /> object containing a description
            ///    of the media represented by the current instance.
            /// </value>
00173             public abstract string Description {get;}
            
            /// <summary>
            ///    Gets the types of media represented by the current
            ///    instance.
            /// </summary>
            /// <value>
            ///    A bitwise combined <see cref="MediaTypes" /> containing
            ///    the types of media represented by the current instance.
            /// </value>
00183             public abstract MediaTypes MediaTypes {get;}
            
            /// <summary>
            ///    Gets the raw Xiph comment data contained in the codec.
            /// </summary>
            /// <value>
            ///    A <see cref="ByteVector" /> object containing a raw Xiph
            ///    comment or <see langword="null"/> if none was found.
            /// </value>
00192             public abstract ByteVector CommentData {get;}
            
            /// <summary>
            ///    Gets the duration of the media represented by the current
            ///    instance.
            /// </summary>
            /// <value>
            ///    Always <see cref="TimeSpan.Zero" />.
            /// </value>
            /// <remarks>
            ///    In order to determine the duration of an Ogg stream, the
            ///    first and last granular positions will be passed to <see
            ///    cref="GetDuration" />.
            /// </remarks>
00206             public TimeSpan Duration {
                  get {return TimeSpan.Zero;}
            }
            
#endregion
            
            
            
#region Private Methods
            
            /// <summary>
            ///    Reads a Ogg packet that has been encountered in the
            ///    stream.
            /// </summary>
            /// <param name="packet">
            ///    A <see cref="ByteVector" /> object containing a packet to
            ///    be read by the current instance.
            /// </param>
            /// <param name="index">
            ///    A <see cref="int" /> value containing the index of the
            ///    packet in the stream.
            /// </param>
            /// <returns>
            ///    <see langword="true" /> if the codec has read all the
            ///    necessary packets for the stream and does not need to be
            ///    called again, typically once the Xiph comment has been
            ///    found. Otherwise <see langword="false" />.
            /// </returns>
            /// <exception cref="ArgumentNullException">
            ///    <paramref name="packet" /> is <see langword="null" />.
            /// </exception>
            /// <exception cref="ArgumentOutOfRangeException">
            ///    <paramref name="index" /> is less than zero.
            /// </exception>
            /// <exception cref="CorruptFileException">
            ///    The data does not conform to the specificiation for the
            ///    codec represented by the current instance.
            /// </exception>
            public abstract bool ReadPacket (ByteVector packet, int index);
            
            /// <summary>
            ///    Computes the duration of the stream using the first and
            ///    last granular positions of the stream.
            /// </summary>
            /// <param name="firstGranularPosition">
            ///    A <see cref="long" /> value containing the first granular
            ///    position of the stream.
            /// </param>
            /// <param name="lastGranularPosition">
            ///    A <see cref="long" /> value containing the last granular
            ///    position of the stream.
            /// </param>
            /// <returns>
            ///    A <see cref="TimeSpan" /> value containing the duration
            ///    of the stream.
            /// </returns>
            public abstract TimeSpan GetDuration (long firstGranularPosition,
                                                  long lastGranularPosition);
            
            /// <summary>
            ///    Replaces the comment packet in a collection of packets
            ///    with the rendered version of a Xiph comment or inserts a
            ///    comment packet if the stream lacks one.
            /// </summary>
            /// <param name="packets">
            ///    A <see cref="ByteVectorCollection" /> object containing
            ///    a collection of packets.
            /// </param>
            /// <param name="comment">
            ///    A <see cref="XiphComment" /> object to store the rendered
            ///    version of in <paramref name="packets" />.
            /// </param>
            /// <exception cref="ArgumentNullException">
            ///    <paramref name="packets" /> or <paramref name="comment"
            ///    /> is <see langword="null" />.
            /// </exception>
            public abstract void SetCommentPacket (ByteVectorCollection packets,
                                                   XiphComment comment);
            
#endregion
      }
}

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