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XingHeader.cs

//
// XingHeader.cs: Provides information about a variable bitrate MPEG audio
// stream.
//
// Author:
//   Brian Nickel (brian.nickel@gmail.com)
//
// Original Source:
//   xingheader.cpp from TagLib
//
// Copyright (C) 2005-2007 Brian Nickel
// Copyright (C) 2003 by Ismael Orenstein (Original Implementation)
// 
// 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.Collections;
using System;

namespace TagLib.Mpeg {
      /// <summary>
      ///    This structure provides information about a variable bitrate MPEG
      ///    audio stream.
      /// </summary>
00037       public struct XingHeader
      {
            #region Private Fields
            
            /// <summary>
            ///    Contains the frame count.
            /// </summary>
00044             private uint frames;
            
            /// <summary>
            ///    Contains the stream size.
            /// </summary>
00049             private uint size;
            
            /// <summary>
            ///    Indicates that a physical Xing header is present.
            /// </summary>
00054             private bool present;
            
            #endregion
            
            
            
            #region Public Fields
            
            /// <summary>
            ///    Contains te Xing identifier.
            /// </summary>
            /// <value>
            ///    "Xing"
            /// </value>
00068             public static readonly ReadOnlyByteVector FileIdentifier = "Xing";
            
            /// <summary>
            ///    An empty and unset Xing header.
            /// </summary>
00073             public static readonly XingHeader Unknown = new XingHeader (0, 0);
            
            #endregion
            
            
            
            #region Constructors
            
            /// <summary>
            ///    Constructs and initializes a new instance of <see
            ///    cref="XingHeader" /> with a specified frame count and
            ///    size.
            /// </summary>
            /// <param name="frame">
            ///    A <see cref="uint" /> value specifying the frame count of
            ///    the audio represented by the new instance.
            /// </param>
            /// <param name="size">
            ///    A <see cref="uint" /> value specifying the stream size of
            ///    the audio represented by the new instance.
            /// </param>
00094             private XingHeader (uint frame, uint size)
            {
                  this.frames = frame;
                  this.size = size;
                  this.present = false;
            }
            
            /// <summary>
            ///    Constructs and initializes a new instance of <see
            ///    cref="XingHeader" /> by reading its raw contents.
            /// </summary>
            /// <param name="data">
            ///    A <see cref="ByteVector" /> object containing the raw
            ///    Xing header.
            /// </param>
            /// <exception cref="ArgumentNullException">
            ///    <paramref name="data" /> is <see langword="null" />.
            /// </exception>
            /// <exception cref="CorruptFileException">
            ///    <paramref name="data" /> does not start with <see
            ///    cref="FileIdentifier" />.
            /// </exception>
00116             public XingHeader (ByteVector data)
            {
                  if (data == null)
                        throw new ArgumentNullException ("data");
                  
                  // Check to see if a valid Xing header is available.
                  if (!data.StartsWith (FileIdentifier))
                        throw new CorruptFileException (
                              "Not a valid Xing header");
                  
                  int position = 8;
                  
                  if ((data [7] & 0x01) != 0) {
                        frames = data.Mid (position, 4).ToUInt ();
                        position += 4;
                  } else
                        frames = 0;
                  
                  if ((data [7] & 0x02) != 0) {
                        size = data.Mid (position, 4).ToUInt ();
                        position += 4;
                  } else
                        size = 0;
                  
                  present = true;
            }
            
            #endregion
            
            
            
            #region Public Properties
            
            /// <summary>
            ///    Gets the total number of frames in the file, as indicated
            ///    by the current instance.
            /// </summary>
            /// <value>
            ///    A <see cref="uint" /> value containing the number of
            ///    frames in the file, or <c>0</c> if not specified.
            /// </value>
00157             public uint TotalFrames {
                  get {return frames;}
            }
            
            /// <summary>
            ///    Gets the total size of the file, as indicated by the
            ///    current instance.
            /// </summary>
            /// <value>
            ///    A <see cref="uint" /> value containing the total size of
            ///    the file, or <c>0</c> if not specified.
            /// </value>
00169             public uint TotalSize {
                  get {return size;}
            }
            
            /// <summary>
            ///    Gets whether or not a physical Xing header is present in
            ///    the file.
            /// </summary>
            /// <value>
            ///    A <see cref="bool" /> value indicating whether or not the
            ///    current instance represents a physical Xing header.
            /// </value>
00181             public bool Present {
                  get {return present;}
            }
            
            #endregion
            
            
            
            #region Public Static Methods
            
            /// <summary>
            ///    Gets the offset at which a Xing header would appear in an
            ///    MPEG audio packet based on the version and channel mode.
            /// </summary>
            /// <param name="version">
            ///    A <see cref="Version" /> value specifying the version of
            ///    the MPEG audio packet.
            /// </param>
            /// <param name="channelMode">
            ///    A <see cref="ChannelMode" /> value specifying the channel
            ///    mode of the MPEG audio packet.
            /// </param>
            /// <returns>
            ///    A <see cref="int" /> value indicating the offset in an
            ///    MPEG audio packet at which the Xing header would appear.
            /// </returns>
00207             public static int XingHeaderOffset (Version version,
                                                ChannelMode channelMode)
            {
                  bool single_channel =
                        channelMode == ChannelMode.SingleChannel;
                  
                  if (version == Version.Version1)
                        return single_channel ? 0x15 : 0x24;
                  else
                        return single_channel ? 0x0D : 0x15;
            }
            
            #endregion
      }
}

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