private void WriteVbrHeader(bool isPlaceholder)
{
var buffer = new byte[GetFrameLength(this.mpegVersion, 64000, this.sampleRate, 0)];
if (!isPlaceholder)
{
uint header = this.firstFrameHeader;
int dataOffset = GetFrameDataOffset(this.mpegVersion, this.channelMode);
header &= 0xFFFE0DFF; // Clear CRC, bitrate, and padding fields
header |= (uint)(mpegVersion == 3 ? 5 : 8) << 12; // 64 kbit/sec
BitHelper.CopyBytes(buffer, 0, BigEndianBitConverter.GetBytes(header));
BitHelper.CopyBytes(buffer, dataOffset, BigEndianBitConverter.GetBytes(0x58696E67)); // "Xing"
BitHelper.CopyBytes(buffer, dataOffset + 4, BigEndianBitConverter.GetBytes((uint)0x7)); // Flags
BitHelper.CopyBytes(buffer, dataOffset + 8, BigEndianBitConverter.GetBytes((uint)frameOffsets.Count)); // Frame count
BitHelper.CopyBytes(buffer, dataOffset + 12, BigEndianBitConverter.GetBytes(totalFrameLength)); // File length
for (int i = 0; i < 100; i++)
{
int frameIndex = (int)((i / 100.0) * this.frameOffsets.Count);
buffer[dataOffset + 16 + i] = (byte)(this.frameOffsets[frameIndex] / (double)this.totalFrameLength * 256.0);
}
}
this.fileStream.Write(buffer, 0, 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);
}
}
