public bool Initialize(byte[] i_Header, int i_StartLocation)
{
m_StartLocation = i_StartLocation;
m_Valid = true;
if (i_Header.Length != 4)
{
Debugger.Trace("Received an invalid sized Header");
m_Valid = false;
}
if (i_Header[0] != 0xFF || (i_Header[1] & 0xE0) != 0xE0)
{
Debugger.Trace("Received an invalid Header");
m_Valid = false;
}
// MPEG Audio version ID
// 00 - MPEG Version 2.5 (later extension of MPEG 2)
// 01 - reserved
// 10 - MPEG Version 2 (ISO/IEC 13818-3)
// 11 - MPEG Version 1 (ISO/IEC 11172-3)
// Note: MPEG Version 2.5 was added lately to the MPEG 2 standard.
// It is an extension used for very low bitrate files, allowing the use of lower sampling frequencies.
// If your decoder does not support this extension, it is recommended for you to use 12 bits for synchronization instead of 11 bits.
int VersionID = (i_Header[1] >> 3) & 0x3;
switch (VersionID)
{
case 0:
m_Version = MPEG_Version.MPEG_2_5;
break;
case 1:
m_Version = MPEG_Version.INVALID;
m_Valid = false;
break;
case 2:
m_Version = MPEG_Version.MPEG_2;
break;
case 3:
m_Version = MPEG_Version.MPEG_1;
break;
default:
m_Version = MPEG_Version.INVALID;
m_Valid = false;
break;
}
// Layer description
// 00 - reserved
// 01 - Layer III
// 10 - Layer II
// 11 - Layer I
int LayerID = (i_Header[1] & 0x06) >> 1;
switch (LayerID)
{
case 0:
m_Layer = MPEG_Layer.INVALID;
m_Valid = false;
break;
case 1:
m_Layer = MPEG_Layer.LAYER_III;
break;
case 2:
m_Layer = MPEG_Layer.LAYER_II;
break;
case 3:
m_Layer = MPEG_Layer.LAYER_I;
break;
default:
m_Layer = MPEG_Layer.INVALID;
m_Valid = false;
break;
}
// Protection bit
// 0 - Protected by CRC (16bit CRC follows header)
// 1 - Not protected
m_Protected = (i_Header[1] & 0x01) == 0x00;
// Bitrate index
m_BitRateIndex = (i_Header[2] & 0xF0) >> 4;
if (m_Valid && (int)m_Version < 3 && (int)m_Layer < 3)
m_BitRate = BitRates[(int)m_Version][(int)m_Layer][m_BitRateIndex];
else
m_BitRate = -1;
if (m_BitRate < 0)
m_Valid = false;
// MPEG layer II doesnt allow some bitrates
// bitrate single stereo intensity dual
// free yes yes yes yes
// 32 yes no no no
// 48 yes no no no
// 56 yes no no no
// 64 yes yes yes yes
// 80 yes no no no
// 96 yes yes yes yes
// 112 yes yes yes yes
// 128 yes yes yes yes
// 160 yes yes yes yes
// 192 yes yes yes yes
// 224 no yes yes yes
// 256 no yes yes yes
// 320 no yes yes yes
// 384 no yes yes yes
if (m_Valid && m_Layer == MPEG_Layer.LAYER_II)
{
if (m_ChannelMode == MPEG_CHANNEL_MODE.SINGLE_CHANNEL)
{
if (m_BitRate == 224)
m_Valid = false;
else if (m_BitRate == 256)
m_Valid = false;
else if (m_BitRate == 320)
m_Valid = false;
else if (m_BitRate == 384)
m_Valid = false;
}
else
{
if (m_BitRate == 32)
m_Valid = false;
else if (m_BitRate == 48)
m_Valid = false;
else if (m_BitRate == 56)
m_Valid = false;
else if (m_BitRate == 80)
m_Valid = false;
}
}
// Convert bitrate to Hz
m_BitRate *= 1000;
// bits MPEG1 MPEG2 MPEG2.5
// 00 44100 Hz 22050 Hz 11025 Hz
// 01 48000 Hz 24000 Hz 12000 Hz
// 10 32000 Hz 16000 Hz 8000 Hz
// 11 reserved reserved reserved
int SampleRateIndex = (i_Header[2] & 0x0C) >> 2;
switch (SampleRateIndex)
{
case 0:
switch (m_Version)
{
case MPEG_Version.MPEG_1:
m_SampleRate = 44100;
break;
case MPEG_Version.MPEG_2:
m_SampleRate = 22050;
break;
case MPEG_Version.MPEG_2_5:
m_SampleRate = 11025;
break;
}
break;
case 1:
switch (m_Version)
{
case MPEG_Version.MPEG_1:
m_SampleRate = 48000;
break;
case MPEG_Version.MPEG_2:
m_SampleRate = 24000;
break;
case MPEG_Version.MPEG_2_5:
m_SampleRate = 12000;
break;
}
break;
case 2:
switch (m_Version)
{
case MPEG_Version.MPEG_1:
m_SampleRate = 32000;
break;
case MPEG_Version.MPEG_2:
m_SampleRate = 16000;
break;
case MPEG_Version.MPEG_2_5:
m_SampleRate = 8000;
break;
}
break;
case 3:
m_SampleRate = -1;
m_Valid = false;
break;
default:
m_SampleRate = -1;
m_Valid = false;
break;
}
// Padding bit
// 0 - frame is not padded
// 1 - frame is padded with one extra slot
// Padding is used to exactly fit the bitrate.As an example: 128kbps 44.1kHz layer II uses a
// lot of 418 bytes and some of 417 bytes long frames to get the exact 128k bitrate. For Layer
// I slot is 32 bits long, for Layer II and Layer III slot is 8 bits long.
m_Padding = (i_Header[2] >> 1) & 0x01;
// Private bit
m_Private = (i_Header[2] & 0x01) == 0x01;
// Channel Mode
// 00 - Stereo
// 01 - Joint stereo (Stereo)
// 10 - Dual channel (2 mono channels)
// 11 - Single channel (Mono)
int ChannelModeID = (i_Header[3] & 0xC0) >> 6;
switch (ChannelModeID)
{
case 0:
m_ChannelMode = MPEG_CHANNEL_MODE.STEREO;
break;
case 1:
m_ChannelMode = MPEG_CHANNEL_MODE.JOINT_STEREO;
break;
case 2:
m_ChannelMode = MPEG_CHANNEL_MODE.DUAL_CHANNEL;
break;
case 3:
m_ChannelMode = MPEG_CHANNEL_MODE.SINGLE_CHANNEL;
break;
}
// Mode extension (used by joint stereo)
m_ModeExtension = (i_Header[3] & 0x30) >> 4;
// Copyright
// 0 - Audio is not copyrighted
// 1 - Audio is copyrighted
m_Copyright = (i_Header[3] & 0x08) != 0x00;
// Original
// 0 - Copy of original media
// 1 - Original media
m_Original = (i_Header[3] & 0x04) != 0x00;
// Emphasis
// 00 - none
// 01 - 50/15 ms
// 10 - reserved
// 11 - CCIT J.17
int EmphasisID = i_Header[3] & 0x03;
switch (EmphasisID)
{
case 0:
m_Emphasis = MPEG_Emphasis.NONE;
break;
case 1:
m_Emphasis = MPEG_Emphasis.MS_50_15;
break;
case 2:
m_Emphasis = MPEG_Emphasis.RESERVED;
break;
case 3:
m_Emphasis = MPEG_Emphasis.CCIT_J_17;
break;
}
// Determine the samples per Frame
// MPEG 1 MPEG 2 (LSF) MPEG 2.5 (LSF)
// Layer I 384 384 384
// Layer II 1152 1152 1152
// Layer III 1152 576 576
switch(m_Layer)
{
case MPEG_Layer.LAYER_I:
m_SamplesPerFrame = 384;
break;
case MPEG_Layer.LAYER_II:
m_SamplesPerFrame = 1152;
break;
case MPEG_Layer.LAYER_III:
if (m_Version == MPEG_Version.MPEG_1)
m_SamplesPerFrame = 1152;
else
m_SamplesPerFrame = 576;
break;
}
// Calculate the Frame Size
if (m_Valid && m_SampleRate != 0)
{
m_FrameSize = ( (m_SamplesPerFrame / 8 * m_BitRate) / m_SampleRate) + m_Padding;
}
else
{
m_FrameSize = -1;
}
if (m_FrameSize <= 0)
m_Valid = false;
return m_Valid;
}
public MP3Header()
{
m_Valid = false;
m_Version = MPEG_Version.INVALID;
m_Layer = MPEG_Layer.INVALID;
m_Protected = false;
m_BitRateIndex = -1;
m_BitRate = -1;
m_SampleRate = -1;
m_Padding = -1;
m_Private = false;
m_ChannelMode = MPEG_CHANNEL_MODE.STEREO;
m_ModeExtension = -1;
m_Copyright = false;
m_Original = false;
m_Emphasis = MPEG_Emphasis.NONE;
m_FrameSize = -1;
m_StartLocation = -1;
}