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);
}
}
}
private static int GetSlots(MpegFrame frame)
{
int cnt = frame.FrameLength - 4;
if (frame.HasCrc)
{
cnt -= 2;
}
if (frame.Version == MpegVersion.Version1 && frame.ChannelMode != MpegChannelMode.Mono)
{
return(cnt - 32);
}
if (frame.Version > MpegVersion.Version1 && frame.ChannelMode == MpegChannelMode.Mono)
{
return(cnt - 9);
}
return(cnt - 17);
}
// this just reads the channel mode and set a few flags
private void InitFrame(MpegFrame frame)
{
switch (frame.ChannelMode)
{
case MpegChannelMode.Mono:
_channels = 1;
_jsbound = SBLIMIT;
break;
case MpegChannelMode.JointStereo:
_channels = 2;
_jsbound = frame.ChannelModeExtension * 4 + 4;
break;
default:
_channels = 2;
_jsbound = SBLIMIT;
break;
}
}
public override int DecodeFrame(MpegFrame frame, Span <float> ch0, Span <float> ch1)
{
InitFrame(frame);
int[] rateTable = GetRateTable(frame);
ReadAllocation(frame, rateTable);
for (int i = 0; i < _scfsi[0].Length; i++)
{
// Since Layer II has to know which subbands have energy,
// we use the "Layer I valid" selection to mark that energy is present.
// That way Layer I doesn't have to do anything else.
_scfsi[0][i] = _allocation[0][i] != 0 ? 2 : -1;
_scfsi[1][i] = _allocation[1][i] != 0 ? 2 : -1;
}
ReadScaleFactorSelection(frame, _scfsi, _channels);
ReadScaleFactors(frame);
ReadSamples(frame);
return(DecodeSamples(ch0, ch1));
}
internal MpegFrame NextFrame()
{
// if _current is null, we've returned the last frame already
var frame = _current;
if (frame != null)
{
if (_canSeek)
{
frame.SaveBuffer();
DiscardThrough(frame.Offset + frame.FrameLength, false);
}
if (frame == _last && !_endFound)
{
do
{
FindNextFrame();
} while (frame == _last && !_endFound);
}
_current = frame.Next;
if (!_canSeek)
{
// if we're in a forward-only stream, don't bother keeping the frames that have already been processed
lock (_frameLock)
{
var temp = _first;
_first = temp.Next;
temp.Next = null;
}
}
}
return(frame);
}
FrameBase FindNextFrame()
{
// if we've found the end, don't bother looking for anything else
if (_endFound)
{
return(null);
}
var freeFrame = _lastFree;
var lastFrameStart = _readOffset;
lock (_frameLock)
{
// read 3 bytes
var syncBuf = new byte[4];
try
{
if (Read(_readOffset, syncBuf, 0, 4) == 4)
{
// now loop until a frame is found
do
{
var sync = (uint)(syncBuf[0] << 24 | syncBuf[1] << 16 | syncBuf[2] << 8 | syncBuf[3]);
lastFrameStart = _readOffset;
// try ID3 first (for v2 frames)
if (_id3Frame == null)
{
var f = ID3Frame.TrySync(sync);
if (f != null)
{
if (f.Validate(_readOffset, this))
{
if (!_canSeek)
{
f.SaveBuffer();
}
_readOffset += f.Length;
DiscardThrough(_readOffset, true);
return(_id3Frame = f);
}
}
}
// now look for a RIFF header
if (_first == null && _riffHeaderFrame == null)
{
var f = RiffHeaderFrame.TrySync(sync);
if (f != null)
{
if (f.Validate(_readOffset, this))
{
_readOffset += f.Length;
DiscardThrough(_readOffset, true);
return(_riffHeaderFrame = f);
}
}
}
// finally, just try for an MPEG frame
var frame = MpegFrame.TrySync(sync);
if (frame != null)
{
if (frame.Validate(_readOffset, this) &&
!(freeFrame != null &&
(frame.Layer != freeFrame.Layer ||
frame.Version != freeFrame.Version ||
frame.SampleRate != freeFrame.SampleRate ||
frame.BitRateIndex > 0
)
)
)
{
if (!_canSeek)
{
frame.SaveBuffer();
DiscardThrough(_readOffset + frame.FrameLength, true);
}
_readOffset += frame.FrameLength;
if (_first == null)
{
if (_vbrInfo == null && (_vbrInfo = frame.ParseVBR()) != null)
{
return(FindNextFrame());
}
else
{
frame.Number = 0;
_first = _last = frame;
}
}
else
{
if (frame.SampleCount != _first.SampleCount)
{
_mixedFrameSize = true;
}
frame.SampleOffset = _last.SampleCount + _last.SampleOffset;
frame.Number = _last.Number + 1;
_last = (_last.Next = frame);
}
if (frame.BitRateIndex == 0)
{
_lastFree = frame;
}
return(frame);
}
}
// if we've read MPEG frames and can't figure out what frame type we have, try looking for a new ID3 tag
if (_last != null)
{
var f = ID3Frame.TrySync(sync);
if (f != null)
{
if (f.Validate(_readOffset, this))
{
if (!_canSeek)
{
f.SaveBuffer();
}
// if it's a v1 tag, go ahead and parse it
if (f.Version == 1)
{
_id3v1Frame = f;
}
else
{
// grrr... the ID3 2.4 spec says tags can be anywhere in the file and that later tags can override earlier ones... boo
_id3Frame.Merge(f);
}
_readOffset += f.Length;
DiscardThrough(_readOffset, true);
return(f);
}
}
}
// well, we didn't find anything, so rinse and repeat with the next byte
++_readOffset;
if (_first == null || !_canSeek)
{
DiscardThrough(_readOffset, true);
}
Buffer.BlockCopy(syncBuf, 1, syncBuf, 0, 3);
} while (Read(_readOffset + 3, syncBuf, 3, 1) == 1);
}
// move the "end of frame" marker for the last free format frame (in case we have one)
// this is because we don't include the last four bytes otherwise
lastFrameStart += 4;
_endFound = true;
return(null);
}
finally
{
if (freeFrame != null)
{
freeFrame.Length = (int)(lastFrameStart - freeFrame.Offset);
if (!_canSeek)
{
// gotta finish filling the buffer!!
throw new InvalidOperationException("Free frames cannot be read properly from forward-only streams!");
}
// if _lastFree hasn't changed (we got a non-MPEG frame), clear it out
if (_lastFree == freeFrame)
{
_lastFree = null;
}
}
}
}
}
FrameBase FindNextFrame()
{
// if we've found the end, don't bother looking for anything else
if (_endFound) return null;
var freeFrame = _lastFree;
var lastFrameStart = _readOffset;
lock (_frameLock)
{
// read 3 bytes
var syncBuf = new byte[4];
try
{
if (Read(_readOffset, syncBuf, 0, 4) == 4)
{
// now loop until a frame is found
do
{
var sync = (uint)(syncBuf[0] << 24 | syncBuf[1] << 16 | syncBuf[2] << 8 | syncBuf[3]);
lastFrameStart = _readOffset;
// try ID3 first (for v2 frames)
if (_id3Frame == null)
{
var f = ID3Frame.TrySync(sync);
if (f != null)
{
if (f.Validate(_readOffset, this))
{
if (!_canSeek) f.SaveBuffer();
_readOffset += f.Length;
DiscardThrough(_readOffset, true);
return _id3Frame = f;
}
}
}
// now look for a RIFF header
if (_first == null && _riffHeaderFrame == null)
{
var f = RiffHeaderFrame.TrySync(sync);
if (f != null)
{
if (f.Validate(_readOffset, this))
{
_readOffset += f.Length;
DiscardThrough(_readOffset, true);
return _riffHeaderFrame = f;
}
}
}
// finally, just try for an MPEG frame
var frame = MpegFrame.TrySync(sync);
if (frame != null)
{
if (frame.Validate(_readOffset, this)
&& !(freeFrame != null
&& (frame.Layer != freeFrame.Layer
|| frame.Version != freeFrame.Version
|| frame.SampleRate != freeFrame.SampleRate
|| frame.BitRateIndex > 0
)
)
)
{
if (!_canSeek)
{
frame.SaveBuffer();
DiscardThrough(_readOffset + frame.FrameLength, true);
}
_readOffset += frame.FrameLength;
if (_first == null)
{
if (_vbrInfo == null && (_vbrInfo = frame.ParseVBR()) != null)
{
return FindNextFrame();
}
else
{
frame.Number = 0;
_first = _last = frame;
}
}
else
{
if (frame.SampleCount != _first.SampleCount)
{
_mixedFrameSize = true;
}
frame.SampleOffset = _last.SampleCount + _last.SampleOffset;
frame.Number = _last.Number + 1;
_last = (_last.Next = frame);
}
if (frame.BitRateIndex == 0)
{
_lastFree = frame;
}
return frame;
}
}
// if we've read MPEG frames and can't figure out what frame type we have, try looking for a new ID3 tag
if (_last != null)
{
var f = ID3Frame.TrySync(sync);
if (f != null)
{
if (f.Validate(_readOffset, this))
{
if (!_canSeek) f.SaveBuffer();
// if it's a v1 tag, go ahead and parse it
if (f.Version == 1)
{
_id3v1Frame = f;
}
else
{
// grrr... the ID3 2.4 spec says tags can be anywhere in the file and that later tags can override earlier ones... boo
_id3Frame.Merge(f);
}
_readOffset += f.Length;
DiscardThrough(_readOffset, true);
return f;
}
}
}
// well, we didn't find anything, so rinse and repeat with the next byte
++_readOffset;
if (_first == null || !_canSeek) DiscardThrough(_readOffset, true);
Buffer.BlockCopy(syncBuf, 1, syncBuf, 0, 3);
} while (Read(_readOffset + 3, syncBuf, 3, 1) == 1);
}
// move the "end of frame" marker for the last free format frame (in case we have one)
// this is because we don't include the last four bytes otherwise
lastFrameStart += 4;
_endFound = true;
return null;
}
finally
{
if (freeFrame != null)
{
freeFrame.Length = (int)(lastFrameStart - freeFrame.Offset);
if (!_canSeek)
{
// gotta finish filling the buffer!!
throw new InvalidOperationException("Free frames cannot be read properly from forward-only streams!");
}
// if _lastFree hasn't changed (we got a non-MPEG frame), clear it out
if (_lastFree == freeFrame)
{
_lastFree = null;
}
}
}
}
}
public abstract int DecodeFrame(MpegFrame frame, Span <float> ch0, Span <float> ch1);
static internal bool GetCRC(MpegFrame frame, ref uint crc)
{
return LayerIIDecoderBase.GetCRC(frame, _rateTable, _allocLookupTable, false, ref crc);
}
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;
}
static internal bool GetCRC(MpegFrame frame, ref uint crc)
{
return(LayerIIDecoderBase.GetCRC(frame, _rateTable, _allocLookupTable, false, ref crc));
}
static internal bool GetCRC(MpegFrame frame, ref uint crc)
{
return LayerIIDecoderBase.GetCRC(frame, SelectTable(frame), _allocLookupTable, true, ref crc);
}
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);
}
protected abstract int[] GetRateTable(MpegFrame frame);
internal MpegFrame NextFrame()
{
// if _current is null, we've returned the last frame already
var frame = _current;
if (frame != null)
{
if (_canSeek)
{
frame.SaveBuffer();
DiscardThrough(frame.Offset + frame.FrameLength, false);
}
if (frame == _last && !_endFound)
{
do
{
FindNextFrame();
} while (frame == _last && !_endFound);
}
_current = frame.Next;
if (!_canSeek)
{
// if we're in a forward-only stream, don't bother keeping the frames that have already been processed
lock (_frameLock)
{
var temp = _first;
_first = temp.Next;
temp.Next = null;
}
}
}
return frame;
}
protected abstract void ReadScaleFactorSelection(MpegFrame frame, int[][] scfsi, int channels);
