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Theora.cs

//
// Theora.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;

00026 namespace TagLib.Ogg.Codecs
{
      /// <summary>
      ///    This class extends <see cref="Codec" /> and implements <see
      ///    cref="IVideoCodec" /> to provide support for processing Ogg
      ///    Theora bitstreams.
      /// </summary>
00033       public class Theora : Codec, IVideoCodec
      {
#region Private Static Fields
            
            /// <summary>
            ///    Contains the file identifier.
            /// </summary>
00040             private static ByteVector id = "theora";
            
#endregion
            
            
            
#region Private Fields
            
            /// <summary>
            ///    Contains the header packet.
            /// </summary>
00051             private HeaderPacket header;
            
            /// <summary>
            ///    Contains the comment data.
            /// </summary>
00056             private ByteVector comment_data;
            
#endregion
            
            
            
#region Constructors
            
            /// <summary>
            ///    Constructs and initializes a new instance of <see
            ///    cref="Theora" />.
            /// </summary>
00068             private Theora ()
            {
            }
            
#endregion
            
            
            
#region Public 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>
00106             public override bool ReadPacket (ByteVector packet, int index)
            {
                  if (packet == null)
                        throw new ArgumentNullException ("packet");
                  
                  if (index < 0)
                        throw new ArgumentOutOfRangeException ("index",
                              "index must be at least zero.");
                  
                  int type = PacketType (packet);
                  if (type != 0x80 && index == 0)
                        throw new CorruptFileException (
                              "Stream does not begin with theora header.");
                  
                  if (comment_data == null) {
                        if (type == 0x80)
                              header = new HeaderPacket (packet);
                        else if (type == 0x81)
                              comment_data = packet.Mid (7);
                        else
                              return true;
                  }
                  
                  return comment_data != null;
            }
            
            /// <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>
00148             public override TimeSpan GetDuration (long firstGranularPosition,
                                                  long lastGranularPosition)
            {
                  return TimeSpan.FromSeconds (
                        header.GranuleTime (lastGranularPosition) -
                        header.GranuleTime (firstGranularPosition));
            }
            
            /// <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>
00173             public override void SetCommentPacket (ByteVectorCollection packets,
                                                   XiphComment comment)
            {
                  if (packets == null)
                        throw new ArgumentNullException ("packets");
                  
                  if (comment == null)
                        throw new ArgumentNullException ("comment");
                  
                  ByteVector data = new ByteVector ((byte) 0x81);
                  data.Add (id);
                  data.Add (comment.Render (true));
                  
                  if (packets.Count > 1 && PacketType (packets [1]) == 0x81)
                        packets [1] = data;
                  else
                        packets.Insert (1, data);
            }
            
#endregion
            
            
            
#region Public Properties
            
            /// <summary>
            ///    Gets the width of the video represented by the current
            ///    instance.
            /// </summary>
            /// <value>
            ///    A <see cref="int" /> value containing the width of the
            ///    video represented by the current instance.
            /// </value>
00206             public int VideoWidth {
                  get {return header.width;}
            }
            
            /// <summary>
            ///    Gets the height of the video represented by the current
            ///    instance.
            /// </summary>
            /// <value>
            ///    A <see cref="int" /> value containing the height of the
            ///    video represented by the current instance.
            /// </value>
00218             public int VideoHeight {
                  get {return header.height;}
            }
            
            /// <summary>
            ///    Gets the types of media represented by the current
            ///    instance.
            /// </summary>
            /// <value>
            ///    Always <see cref="MediaTypes.Video" />.
            /// </value>
00229             public override MediaTypes MediaTypes {
                  get {return MediaTypes.Video;}
            }
            
            /// <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>
00240             public override ByteVector CommentData {
                  get {return comment_data;}
            }
            
            /// <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>
00252             public override string Description {
                  get {
                        return string.Format (
                              "Theora Version {0}.{1} Video",
                              header.major_version,
                              header.minor_version);
                  }
            }
            
#endregion
            
            
            
#region Public Static Methods
            
            /// <summary>
            ///    Implements the <see cref="CodecProvider" /> delegate to
            ///    provide support for recognizing a Theora stream from the
            ///    header packet.
            /// </summary>
            /// <param name="packet">
            ///    A <see cref="ByteVector" /> object containing the stream
            ///    header packet.
            /// </param>
            /// <returns>
            ///    A <see cref="Codec"/> object containing a codec capable
            ///    of parsing the stream of <see langref="null" /> if the
            ///    stream is not a Theora stream.
            /// </returns>
00281             public static Codec FromPacket (ByteVector packet)
            {
                  return (PacketType (packet) == 0x80) ? new Theora () : null;
            }
            
#endregion
            
            
            
#region Private Static Methods
            
            /// <summary>
            ///    Gets the packet type for a specified Theora packet.
            /// </summary>
            /// <param name="packet">
            ///    A <see cref="ByteVector" /> object containing a Theora
            ///    packet.
            /// </param>
            /// <returns>
            ///    A <see cref="int" /> value containing the packet type or
            ///    -1 if the packet is invalid.
            /// </returns>
00303             private static int PacketType (ByteVector packet)
            {
                  if (packet.Count <= id.Count || packet [0] < 0x80)
                        return -1;
                  
                  for (int i = 0; i < id.Count; i ++)
                        if (packet [i + 1] != id [i])
                        return -1;
                  
                  return packet [0];
            }
            
#endregion
            
            /// <summary>
            ///    This structure represents a Theora header packet.
            /// </summary>
00320             private struct HeaderPacket
            {
                  public byte major_version;
                  public byte minor_version;
                  public byte revision_version;
                  public int width;
                  public int height;
                  public int fps_numerator;
                  public int fps_denominator;
                  public int keyframe_granule_shift;
                  
                  public HeaderPacket (ByteVector data)
                  {
                        major_version = data [7];
                        minor_version = data [8];
                        revision_version = data [9];
                        // width = data.Mid (10, 2).ToShort () << 4;
                        // height = data.Mid (12, 2).ToShort () << 4;
                        width = (int) data.Mid (14, 3).ToUInt (); // Frame Width.
                        height = (int) data.Mid (17, 3).ToUInt (); // Frame Height.
                        // Offset X.
                        // Offset Y.
                        fps_numerator = (int) data.Mid (22, 4).ToUInt ();
                        fps_denominator = (int) data.Mid (26, 4).ToUInt ();
                        // Aspect Numerator.
                        // Aspect Denominator.
                        // Colorspace.
                        // Target bitrate.
                        ushort last_bits = data.Mid (40, 2).ToUShort ();
                        keyframe_granule_shift = (last_bits >> 5) & 0x1F;
                  }
                  
                  /// <summary>
                  ///    Converts an absolute granular position into a
                  ///    seconds.
                  /// </summary>
                  /// <param name="granularPosition">
                  ///    A <see cref="long" /> value containing the
                  ///   absolute granular position.
                  /// </param>
                  /// <returns>
                  ///    A <see cref="double" /> value containing the time
                  ///    at <paramref name="granularPosition" /> in
                  ///    seconds.</returns>
                  /// <remarks>
                  ///    Many thanks to the good people at
                  ///    irc://irc.freenode.net#theora for making this
                  ///    code a reality.
                  /// </remarks>
00369                   public double GranuleTime (long granularPosition)
                  {
                        long iframe = granularPosition >>
                              keyframe_granule_shift;
                        long pframe = granularPosition -
                              (iframe << keyframe_granule_shift);
                        return (iframe + pframe) *
                              ((double) fps_denominator /
                              (double) fps_numerator);
                  }
            }
      }
}

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