/**
* Read a 32-bit header from the bitstream.
*/
public void read_header(Bitstream stream, Crc16[] crcp)
{
uint headerstring; // made to a uint for unsigned right-shift used in this function
int channel_bitrate;
bool sync = false;
do
{
headerstring = (uint)stream.syncHeader(syncmode);
_headerstring = (int)headerstring; // E.B
if (syncmode == Bitstream.INITIAL_SYNC)
{
h_version = (int)((headerstring >> 19) & 1);
if (((headerstring >> 20) & 1) == 0) // SZD: MPEG2.5 detection
{
if (h_version == MPEG2_LSF)
{
h_version = MPEG25_LSF;
}
else
{
throw new BitstreamException(Errors.UNKNOWN_ERROR);
}
}
if ((h_sample_frequency = (int)((headerstring >> 10) & 3)) == 3)
{
throw new BitstreamException(Errors.UNKNOWN_ERROR);
}
}
h_layer = (int)(4 - (headerstring >> 17) & 3);
h_protection_bit = (int)((headerstring >> 16) & 1);
h_bitrate_index = (int)((headerstring >> 12) & 0xF);
h_padding_bit = (int)((headerstring >> 9) & 1);
h_mode = (int)((headerstring >> 6) & 3);
h_mode_extension = (int)((headerstring >> 4) & 3);
if (h_mode == JOINT_STEREO)
{
h_intensity_stereo_bound = (h_mode_extension << 2) + 4;
}
else
{
h_intensity_stereo_bound = 0; // should never be used
}
if (((headerstring >> 3) & 1) == 1)
{
h_copyright = true;
}
if (((headerstring >> 2) & 1) == 1)
{
h_original = true;
}
// calculate number of subbands:
if (h_layer == 1)
{
h_number_of_subbands = 32;
}
else
{
channel_bitrate = h_bitrate_index;
// calculate bitrate per channel:
if (h_mode != SINGLE_CHANNEL)
{
if (channel_bitrate == 4)
{
channel_bitrate = 1;
}
else
{
channel_bitrate -= 4;
}
}
if ((channel_bitrate == 1) || (channel_bitrate == 2))
{
if (h_sample_frequency == THIRTYTWO)
{
h_number_of_subbands = 12;
}
else
{
h_number_of_subbands = 8;
}
}
else if ((h_sample_frequency == FOURTYEIGHT) || ((channel_bitrate >= 3) && (channel_bitrate <= 5)))
{
h_number_of_subbands = 27;
}
else
{
h_number_of_subbands = 30;
}
}
if (h_intensity_stereo_bound > h_number_of_subbands)
{
h_intensity_stereo_bound = h_number_of_subbands;
}
// calculate framesize and nSlots
calculate_framesize();
// read framedata:
int framesizeloaded = stream.read_frame_data(framesize);
if ((framesize >= 0) && (framesizeloaded != framesize))
{
// Data loaded does not match to expected framesize,
// it might be an ID3v1 TAG. (Fix 11/17/04).
throw new BitstreamException(Errors.INVALIDFRAME);
}
if (stream.isSyncCurrentPosition(syncmode))
{
if (syncmode == Bitstream.INITIAL_SYNC)
{
syncmode = Bitstream.STRICT_SYNC;
stream.set_syncword(headerstring & 0xFFF80CC0);
}
sync = true;
}
else
{
stream.unreadFrame();
}
}while (!sync);
stream.parse_frame();
if (h_protection_bit == 0)
{
// frame contains a crc checksum
checksum = (short)stream.get_bits(16);
if (crc == null)
{
crc = new Crc16();
}
crc.add_bits((int)headerstring, 16);
crcp[0] = crc;
}
else
{
crcp[0] = null;
}
if (h_sample_frequency == FOURTYFOUR_POINT_ONE)
{
/*
* if (offset == null)
* {
* int max = max_number_of_frames(stream);
* offset = new int[max];
* for(int i=0; i<max; i++) offset[i] = 0;
* }
* // E.B : Investigate more
* int cf = stream.current_frame();
* int lf = stream.last_frame();
* if ((cf > 0) && (cf == lf))
* {
* offset[cf] = offset[cf-1] + h_padding_bit;
* }
* else
* {
* offset[0] = h_padding_bit;
* }
*/
}
}
