/// <summary>
/// Read a 32-bit header from the bitstream.
/// </summary>
internal void read_header(Bitstream stream, Crc16[] crcp)
{
int headerstring;
int channel_bitrate;
bool sync = false;
do
{
headerstring = stream.syncHeader(syncmode);
h_headerstring = headerstring; // E.B
if (syncmode == Bitstream.INITIAL_SYNC)
{
h_version = ((SupportClass.URShift(headerstring, 19)) & 1);
if (((SupportClass.URShift(headerstring, 20)) & 1) == 0)
{
// SZD: MPEG2.5 detection
if (h_version == MPEG2_LSF)
{
h_version = MPEG25_LSF;
}
else
{
throw stream.newBitstreamException(BitstreamErrors.UNKNOWN_ERROR);
}
}
if ((h_sample_frequency = ((SupportClass.URShift(headerstring, 10)) & 3)) == 3)
{
throw stream.newBitstreamException(BitstreamErrors.UNKNOWN_ERROR);
}
}
h_layer = 4 - (SupportClass.URShift(headerstring, 17)) & 3;
h_protection_bit = (SupportClass.URShift(headerstring, 16)) & 1;
h_bitrate_index = (SupportClass.URShift(headerstring, 12)) & 0xF;
h_padding_bit = (SupportClass.URShift(headerstring, 9)) & 1;
h_mode = ((SupportClass.URShift(headerstring, 6)) & 3);
h_mode_extension = (SupportClass.URShift(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 (((SupportClass.URShift(headerstring, 3)) & 1) == 1)
{
h_copyright = true;
}
if (((SupportClass.URShift(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:
stream.read_frame_data(framesize);
if (stream.IsSyncCurrentPosition(syncmode))
{
if (syncmode == Bitstream.INITIAL_SYNC)
{
syncmode = Bitstream.STRICT_SYNC;
stream.SetSyncWord(headerstring & unchecked ((int)0xFFF80CC0));
}
sync = true;
}
else
{
stream.unreadFrame();
}
} while (!sync);
stream.ParseFrame();
if (h_protection_bit == 0)
{
// frame contains a crc checksum
checksum = (short)stream.GetBitsFromBuffer(16);
if (crc == null)
{
crc = new Crc16();
}
crc.add_bits(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;
* }
* // Bizarre, y avait ici une acollade ouvrante
* 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;
* }
*/
}
}