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/***************************************************************************
copyright : (C) 2005 by Brian Nickel
email : brian.nickel@gmail.com
based on : mpegheader.cpp from TagLib
***************************************************************************/
/***************************************************************************
* 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
{
public enum Version
{
Version1 = 0, // MPEG Version 1
Version2 = 1, // MPEG Version 2
Version2_5 = 2 // MPEG Version 2.5
}
public enum ChannelMode
{
Stereo = 0, // Stereo
JointStereo = 1, // Stereo
DualChannel = 2, // Dual Mono
SingleChannel = 3 // Mono
};
public class Header
{
//////////////////////////////////////////////////////////////////////////
// private properties
//////////////////////////////////////////////////////////////////////////
private bool is_valid;
private Version version;
private int layer;
private bool protection_enabled;
private int bitrate;
private int sample_rate;
private bool is_padded;
private ChannelMode channel_mode;
private bool is_copyrighted;
private bool is_original;
private int frame_length;
//////////////////////////////////////////////////////////////////////////
// public methods
//////////////////////////////////////////////////////////////////////////
public Header (ByteVector data)
{
is_valid = false;
version = Version.Version1;
layer = 0;
protection_enabled = false;
bitrate = 0;
sample_rate = 0;
is_padded = false;
channel_mode = ChannelMode.Stereo;
is_copyrighted = false;
is_original = false;
frame_length = 0;
Parse (data);
}
public Header (Header header)
{
is_valid = header.IsValid;
version = header.Version;
layer = header.Layer;
protection_enabled = header.ProtectionEnabled;
bitrate = header.Bitrate;
sample_rate = header.SampleRate;
is_padded = header.IsPadded;
channel_mode = header.ChannelMode;
is_copyrighted = header.IsCopyrighted;
is_original = header.IsOriginal;
frame_length = header.FrameLength;
}
//////////////////////////////////////////////////////////////////////////
// public properties
//////////////////////////////////////////////////////////////////////////
public bool IsValid {get {return is_valid;}}
public Version Version {get {return version;}}
public int Layer {get {return layer;}}
public bool ProtectionEnabled {get {return protection_enabled;}}
public int Bitrate {get {return bitrate;}}
public int SampleRate {get {return sample_rate;}}
public bool IsPadded {get {return is_padded;}}
public ChannelMode ChannelMode {get {return channel_mode;}}
public bool IsCopyrighted {get {return is_copyrighted;}}
public bool IsOriginal {get {return is_original;}}
public int FrameLength {get {return frame_length;}}
//////////////////////////////////////////////////////////////////////////
// private methods
//////////////////////////////////////////////////////////////////////////
private void Parse (ByteVector data)
{
if(data.Count < 4 || data [0] != 0xff)
{
Debugger.Debug ("Mpeg.Header.Parse () -- First byte did not mactch MPEG synch.");
return;
}
uint flags = data.ToUInt();
// Check for the second byte's part of the MPEG synch
if ((flags & 0xFFE00000) != 0xFFE00000)
{
Debugger.Debug ("Mpeg.Header.Parse () -- Second byte did not mactch MPEG synch.");
return;
}
// Set the MPEG version
switch ((flags >> 19) & 0x03)
{
case 0: version = Version.Version2_5; break;
case 2: version = Version.Version2; break;
case 3: version = Version.Version1; break;
}
// Set the MPEG layer
switch ((flags >> 17) & 0x03)
{
case 1: layer = 3; break;
case 2: layer = 2; break;
case 3: layer = 1; break;
}
protection_enabled = ((flags >>16) & 1) == 0;
// Set the bitrate
int [,,] bitrates = new int [2,3,16] {
{ // Version 1
{ 0, 32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448, 0 }, // layer 1
{ 0, 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384, 0 }, // layer 2
{ 0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 0 } // layer 3
},
{ // Version 2 or 2.5
{ 0, 32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256, 0 }, // layer 1
{ 0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, 0 }, // layer 2
{ 0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, 0 } // layer 3
}
};
int version_index = version == Version.Version1 ? 0 : 1;
int layer_index = layer > 0 ? layer - 1 : 0;
// The bitrate index is encoded as the first 4 bits of the 3rd byte,
// i.e. 1111xxxx
int i = (int) (flags >> 12) & 0x0F;
bitrate = bitrates [version_index,layer_index,i];
// Set the sample rate
int [,] sample_rates = new int [3,4] {
{ 44100, 48000, 32000, 0 }, // Version 1
{ 22050, 24000, 16000, 0 }, // Version 2
{ 11025, 12000, 8000, 0 } // Version 2.5
};
// The sample rate index is encoded as two bits in the 3nd byte,
// i.e. xxxx11xx
i = (int) (flags >> 10) & 0x03;
sample_rate = sample_rates [(int) version,i];
if(sample_rate == 0)
{
Debugger.Debug ("Mpeg.Header.Parse () -- Invalid sample rate.");
return;
}
// The channel mode is encoded as a 2 bit value at the end of the 3nd
// byte, i.e. xxxxxx11
channel_mode = (ChannelMode)((flags >> 16) & 0x3);
// TODO: Add mode extension for completeness
is_copyrighted = (flags & 1) == 1;
is_original = ((flags >> 1) & 1) == 1;
// Calculate the frame length
if(layer == 1)
frame_length = 24000 * 2 * bitrate / sample_rate + (IsPadded ? 1 : 0);
else if (layer == 3)
frame_length = 144000 * bitrate / sample_rate + (IsPadded ? 1 : 0);
else
frame_length = 144000 * bitrate / sample_rate / (version == Version.Version1 ? 1 : 2) + (IsPadded ? 1 : 0);
// Now that we're done parsing, set this to be a valid frame.
is_valid = true;
}
}
}
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