private void ParseMp3Frames(byte[] buffer)
{
var mpeg1BitRate = new[] { 0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 0 };
var mpeg2XBitRate = new[] { 0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, 0 };
var mpeg1SampleRate = new[] { 44100, 48000, 32000, 0 };
var mpeg20SampleRate = new[] { 22050, 24000, 16000, 0 };
var mpeg25SampleRate = new[] { 11025, 12000, 8000, 0 };
int offset = 0;
int length = buffer.Length;
while (length >= 4)
{
int mpegVersion, sampleRate, channelMode;
ulong header = (ulong)BigEndianBitConverter.ToUInt32(buffer, offset) << 32;
if (BitHelper.Read(ref header, 11) != 0x7FF)
{
break;
}
mpegVersion = BitHelper.Read(ref header, 2);
int layer = BitHelper.Read(ref header, 2);
BitHelper.Read(ref header, 1);
int bitRate = BitHelper.Read(ref header, 4);
sampleRate = BitHelper.Read(ref header, 2);
int padding = BitHelper.Read(ref header, 1);
BitHelper.Read(ref header, 1);
channelMode = BitHelper.Read(ref header, 2);
if (mpegVersion == 1 || layer != 1 || bitRate == 0 || bitRate == 15 || sampleRate == 3)
{
break;
}
bitRate = (mpegVersion == 3 ? mpeg1BitRate[bitRate] : mpeg2XBitRate[bitRate]) * 1000;
switch (mpegVersion)
{
case 2:
sampleRate = mpeg20SampleRate[sampleRate];
break;
case 3:
sampleRate = mpeg1SampleRate[sampleRate];
break;
default:
sampleRate = mpeg25SampleRate[sampleRate];
break;
}
int frameLenght = GetFrameLength(mpegVersion, bitRate, sampleRate, padding);
if (frameLenght > length)
{
break;
}
bool isVbrHeaderFrame = false;
if (frameOffsets.Count == 0)
{
// Check for an existing VBR header just to be safe (I haven't seen any in FLVs)
int o = offset + GetFrameDataOffset(mpegVersion, channelMode);
if (BigEndianBitConverter.ToUInt32(buffer, o) == 0x58696E67)
{
// "Xing"
isVbrHeaderFrame = true;
this.delayWrite = false;
this.hasVbrHeader = true;
}
}
if (!isVbrHeaderFrame)
{
if (this.firstBitRate == 0)
{
this.firstBitRate = bitRate;
this.mpegVersion = mpegVersion;
this.sampleRate = sampleRate;
this.channelMode = channelMode;
this.firstFrameHeader = BigEndianBitConverter.ToUInt32(buffer, offset);
}
else if (!this.isVbr && bitRate != this.firstBitRate)
{
this.isVbr = true;
if (!this.hasVbrHeader)
{
if (this.delayWrite)
{
this.WriteVbrHeader(true);
this.writeVbrHeader = true;
this.delayWrite = false;
}
else
{
this.warnings.Add("Detected VBR too late, cannot add VBR header.");
}
}
}
}
this.frameOffsets.Add(this.totalFrameLength + (uint)offset);
offset += frameLenght;
length -= frameLenght;
}
this.totalFrameLength += (uint)buffer.Length;
}
public void WriteChunk(byte[] chunk, uint timeStamp)
{
if (chunk.Length < 1)
{
return;
}
if (chunk[0] == 0)
{
// Header
if (chunk.Length < 3)
{
return;
}
ulong bits = (ulong)BigEndianBitConverter.ToUInt16(chunk, 1) << 48;
aacProfile = BitHelper.Read(ref bits, 5) - 1;
sampleRateIndex = BitHelper.Read(ref bits, 4);
channelConfig = BitHelper.Read(ref bits, 4);
if (aacProfile < 0 || aacProfile > 3)
{
throw new AudioExtractionException("Unsupported AAC profile.");
}
if (sampleRateIndex > 12)
{
throw new AudioExtractionException("Invalid AAC sample rate index.");
}
if (channelConfig > 6)
{
throw new AudioExtractionException("Invalid AAC channel configuration.");
}
}
else
{
// Audio data
int dataSize = chunk.Length - 1;
ulong bits = 0;
// Reference: WriteADTSHeader from FAAC's bitstream.c
BitHelper.Write(ref bits, 12, 0xFFF);
BitHelper.Write(ref bits, 1, 0);
BitHelper.Write(ref bits, 2, 0);
BitHelper.Write(ref bits, 1, 1);
BitHelper.Write(ref bits, 2, aacProfile);
BitHelper.Write(ref bits, 4, sampleRateIndex);
BitHelper.Write(ref bits, 1, 0);
BitHelper.Write(ref bits, 3, channelConfig);
BitHelper.Write(ref bits, 1, 0);
BitHelper.Write(ref bits, 1, 0);
BitHelper.Write(ref bits, 1, 0);
BitHelper.Write(ref bits, 1, 0);
BitHelper.Write(ref bits, 13, 7 + dataSize);
BitHelper.Write(ref bits, 11, 0x7FF);
BitHelper.Write(ref bits, 2, 0);
fileStream.Write(BigEndianBitConverter.GetBytes(bits), 1, 7);
fileStream.Write(chunk, 1, dataSize);
}
}