private void WriteVBRHeader(bool isPlaceholder)
{
var buff = new byte[GetFrameLength(_mpegVersion, 64000, _sampleRate, 0)];
if (!isPlaceholder)
{
var header = _firstFrameHeader;
var dataOffset = GetFrameDataOffset(_mpegVersion, _channelMode);
header &= 0xFFFF0DFF; // Clear bitrate and padding fields
header |= 0x00010000; // Set protection bit (indicates that CRC is NOT present)
header |= (uint)(_mpegVersion == 3 ? 5 : 8) << 12; // 64 kbit/sec
General.CopyBytes(buff, 0, BitConverterBE.GetBytes(header));
General.CopyBytes(buff, dataOffset, BitConverterBE.GetBytes((uint)0x58696E67)); // "Xing"
General.CopyBytes(buff, dataOffset + 4, BitConverterBE.GetBytes((uint)0x7)); // Flags
General.CopyBytes(buff, dataOffset + 8, BitConverterBE.GetBytes((uint)_frameOffsets.Count)); // Frame count
General.CopyBytes(buff, dataOffset + 12, BitConverterBE.GetBytes((uint)_totalFrameLength)); // File length
for (var i = 0; i < 100; i++)
{
var frameIndex = (int)(i / 100.0 * _frameOffsets.Count);
buff[dataOffset + 16 + i] = (byte)(_frameOffsets[frameIndex] / (double)_totalFrameLength * 256.0);
}
}
_fs.Write(buff, 0, buff.Length);
}
public void WriteChunk(byte[] chunk, uint timeStamp)
{
if (chunk.Length < 1)
{
return;
}
if (chunk[0] == 0)
{ // Header
if (chunk.Length < 3)
{
return;
}
var bits = (ulong)BitConverterBE.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 == 4) // HE-AAC
{
_aacProfile = 1; // Uses LC profile + SBR
}
if (_aacProfile < 0 || _aacProfile > 3)
{
throw new Exception("Unsupported AAC profile.");
}
if (_sampleRateIndex > 12)
{
throw new Exception("Invalid AAC sample rate index.");
}
if (_channelConfig > 6)
{
throw new Exception("Invalid AAC channel configuration.");
}
}
else
{ // Audio data
var 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);
_fs.Write(BitConverterBE.GetBytes(bits), 1, 7);
_fs.Write(chunk, 1, dataSize);
}
}
