private void ReadSamples(MpegFrame frame)
{
// load in all the data for this frame (1152 samples in this case)
// NB: we flatten these into output order
for (int ss = 0, idx = 0; ss < SSLIMIT; ss++, idx += SBLIMIT * (_granuleCount - 1))
{
for (int sb = 0; sb < SBLIMIT; sb++, idx++)
{
for (int ch = 0; ch < _channels; ch++)
{
if (ch == 0 || sb < _jsbound)
{
int[] samples = _samples[ch];
int alloc = _allocation[ch][sb];
if (alloc != 0)
{
if (alloc < 0)
{
// grouping (Layer II only, so we don't have to play with the granule count)
int val = frame.ReadBits(-alloc);
int levels = (1 << (-alloc / 2 + -alloc % 2 - 1)) + 1;
samples[idx] = val % levels;
val /= levels;
samples[idx + SBLIMIT] = val % levels;
samples[idx + SBLIMIT * 2] = val / levels;
}
else
{
// non-grouping
for (int gr = 0; gr < _granuleCount; gr++)
{
samples[idx + SBLIMIT * gr] = frame.ReadBits(alloc);
}
}
}
else
{
// no energy... zero out the samples
for (int gr = 0; gr < _granuleCount; gr++)
{
samples[idx + SBLIMIT * gr] = 0;
}
}
}
else
{
int[] samples0 = _samples[0];
int[] samples1 = _samples[1];
// copy chan 0 to chan 1
for (int gr = 0; gr < _granuleCount; gr++)
{
samples1[idx + SBLIMIT * gr] = samples0[idx + SBLIMIT * gr];
}
}
}
}
}
}
private void ReadAllocation(MpegFrame frame, int[] rateTable)
{
var _subBandCount = rateTable.Length;
if (_jsbound > _subBandCount)
{
_jsbound = _subBandCount;
}
Array.Clear(_allocation[0], 0, SBLIMIT);
Array.Clear(_allocation[1], 0, SBLIMIT);
int sb = 0;
for (; sb < _jsbound; sb++)
{
int[] table = _allocLookupTable[rateTable[sb]];
int bits = table[0];
for (int ch = 0; ch < _channels; ch++)
{
_allocation[ch][sb] = table[frame.ReadBits(bits) + 1];
}
}
for (; sb < _subBandCount; sb++)
{
int[] table = _allocLookupTable[rateTable[sb]];
_allocation[0][sb] = _allocation[1][sb] = table[frame.ReadBits(table[0]) + 1];
}
}
private void ReadScaleFactors(MpegFrame frame)
{
for (int sb = 0; sb < SBLIMIT; sb++)
{
for (int ch = 0; ch < _channels; ch++)
{
int[][] scalefac = _scalefac[ch];
switch (_scfsi[ch][sb])
{
case 0:
// all three
scalefac[0][sb] = frame.ReadBits(6);
scalefac[1][sb] = frame.ReadBits(6);
scalefac[2][sb] = frame.ReadBits(6);
break;
case 1:
// only two (2 = 1)
scalefac[0][sb] =
scalefac[1][sb] = frame.ReadBits(6);
scalefac[2][sb] = frame.ReadBits(6);
break;
case 2:
// only one (3 = 2 = 1)
scalefac[0][sb] =
scalefac[1][sb] =
scalefac[2][sb] = frame.ReadBits(6);
break;
case 3:
// only two (3 = 2)
scalefac[0][sb] = frame.ReadBits(6);
scalefac[1][sb] =
scalefac[2][sb] = frame.ReadBits(6);
break;
default:
// none
scalefac[0][sb] = 63;
scalefac[1][sb] = 63;
scalefac[2][sb] = 63;
break;
}
}
}
}
public bool AddBits(MpegFrame frame, int overlap)
{
int originalEnd = _end;
int slots = GetSlots(frame);
while (--slots >= 0)
{
int tmp = frame.ReadBits(8);
if (tmp == -1)
{
ThrowFrameNotEnoughBytes();
}
_buf[++_end] = (byte)tmp;
if (_end == BufferSize - 1)
{
_end = -1;
}
}
_bitsLeft = 8;
if (originalEnd == -1)
{
// it's either the start of the stream or we've reset...
// only return true if overlap says this frame is enough
return(overlap == 0);
}
else
{
// it's not the start of the stream so calculate _start based on whether we have enough bytes left
// if we have enough bytes, reset start to match overlap
if ((originalEnd + 1 - _start + BufferSize) % BufferSize >= overlap)
{
_start = (originalEnd + 1 - overlap + BufferSize) % BufferSize;
return(true);
}
// otherwise, just set start to match the start of the frame (we probably skipped a frame)
else
{
_start = originalEnd;
return(false);
}
}
}
protected static bool GetCRC(
MpegFrame frame, int[] rateTable, int[][] allocLookupTable, bool readScfsiBits, ref uint crc)
{
// ugh... we basically have to re-implement the allocation logic here.
// keep up with how many active subbands we need to read selection info for
var scfsiBits = 0;
// only read as many subbands as we actually need; pay attention to the intensity stereo subbands
var subbandCount = rateTable.Length;
var jsbound = subbandCount;
if (frame.ChannelMode == MpegChannelMode.JointStereo)
{
jsbound = frame.ChannelModeExtension * 4 + 4;
}
// read the full stereo subbands
var channels = frame.ChannelMode == MpegChannelMode.Mono ? 1 : 2;
var sb = 0;
for (; sb < jsbound; sb++)
{
var bits = allocLookupTable[rateTable[sb]][0];
for (int ch = 0; ch < channels; ch++)
{
var alloc = frame.ReadBits(bits);
if (alloc > 0)
{
scfsiBits += 2;
}
MpegFrame.UpdateCRC(alloc, bits, ref crc);
}
}
// read the intensity stereo subbands
for (; sb < subbandCount; sb++)
{
var bits = allocLookupTable[rateTable[sb]][0];
var alloc = frame.ReadBits(bits);
if (alloc > 0)
{
scfsiBits += channels * 2;
}
MpegFrame.UpdateCRC(alloc, bits, ref crc);
}
// finally, read the scalefac selection bits
if (readScfsiBits)
{
while (scfsiBits >= 2)
{
MpegFrame.UpdateCRC(frame.ReadBits(2), 2, ref crc);
scfsiBits -= 2;
}
}
return(true);
}
static internal bool GetCRC(MpegFrame frame, ref uint crc)
{
var cnt = frame.GetSideDataSize();
while (--cnt >= 0)
{
MpegFrame.UpdateCRC(frame.ReadBits(8), 8, ref crc);
}
return true;
}
