unsafe void decode_frame_header(BitReader bitreader, FlacFrame frame)
{
int header_start = bitreader.Position;
if (bitreader.readbits(15) != 0x7FFC)
{
throw new Exception("invalid frame");
}
uint vbs = bitreader.readbit();
frame.bs_code0 = (int)bitreader.readbits(4);
uint sr_code0 = bitreader.readbits(4);
frame.ch_mode = (ChannelMode)bitreader.readbits(4);
uint bps_code = bitreader.readbits(3);
if (Flake.flac_bitdepths[bps_code] != PCM.BitsPerSample)
{
throw new Exception("unsupported bps coding");
}
uint t1 = bitreader.readbit(); // == 0?????
if (t1 != 0)
{
throw new Exception("unsupported frame coding");
}
frame.frame_number = (int)bitreader.read_utf8();
// custom block size
if (frame.bs_code0 == 6)
{
frame.bs_code1 = (int)bitreader.readbits(8);
frame.blocksize = frame.bs_code1 + 1;
}
else if (frame.bs_code0 == 7)
{
frame.bs_code1 = (int)bitreader.readbits(16);
frame.blocksize = frame.bs_code1 + 1;
}
else
{
frame.blocksize = Flake.flac_blocksizes[frame.bs_code0];
}
// custom sample rate
if (sr_code0 < 1 || sr_code0 > 11)
{
// sr_code0 == 12 -> sr == bitreader.readbits(8) * 1000;
// sr_code0 == 13 -> sr == bitreader.readbits(16);
// sr_code0 == 14 -> sr == bitreader.readbits(16) * 10;
throw new Exception("invalid sample rate mode");
}
int frame_channels = (int)frame.ch_mode + 1;
if (frame_channels > 11)
{
throw new Exception("invalid channel mode");
}
if (frame_channels == 2 || frame_channels > 8) // Mid/Left/Right Side Stereo
{
frame_channels = 2;
}
else
{
frame.ch_mode = ChannelMode.NotStereo;
}
if (frame_channels != PCM.ChannelCount)
{
throw new Exception("invalid channel mode");
}
// CRC-8 of frame header
byte crc = do_crc ? crc8.ComputeChecksum(bitreader.Buffer, header_start, bitreader.Position - header_start) : (byte)0;
frame.crc8 = (byte)bitreader.readbits(8);
if (do_crc && frame.crc8 != crc)
{
throw new Exception("header crc mismatch");
}
}
