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;
}
}
}
}
}