/// <summary>
/// Reads decompressed PCM data from our MP3 file.
/// </summary>
public override int Read(byte[] sampleBuffer, int offset, int numBytes)
{
int bytesRead = 0;
lock (repositionLock)
{
if (decompressLeftovers != 0)
{
int toCopy = Math.Min(decompressLeftovers, numBytes);
Array.Copy(decompressBuffer, decompressBufferOffset, sampleBuffer, offset, toCopy);
decompressLeftovers -= toCopy;
if (decompressLeftovers == 0)
{
decompressBufferOffset = 0;
}
else
{
decompressBufferOffset += toCopy;
}
bytesRead += toCopy;
offset += toCopy;
}
while (bytesRead < numBytes)
{
Mp3Frame frame = ReadNextFrame();
if (frame != null)
{
if (repositionedFlag)
{
decompressor.Reset();
repositionedFlag = false;
}
int decompressed = decompressor.DecompressFrame(frame, decompressBuffer, 0);
int toCopy = Math.Min(decompressed, numBytes - bytesRead);
Array.Copy(decompressBuffer, 0, sampleBuffer, offset, toCopy);
if (toCopy < decompressed)
{
decompressBufferOffset = toCopy;
decompressLeftovers = decompressed - toCopy;
}
else
{
// no lefovers
decompressBufferOffset = 0;
decompressLeftovers = 0;
}
offset += toCopy;
bytesRead += toCopy;
}
else
{
break;
}
}
}
Debug.Assert(bytesRead <= numBytes, "MP3 File Reader read too much");
return(bytesRead);
}
/// <summary>
/// Reads decompressed PCM data from our MP3 file.
/// </summary>
public override int Read(byte[] sampleBuffer, int offset, int numBytes)
{
int bytesRead = 0;
lock (repositionLock)
{
if (decompressLeftovers != 0)
{
int toCopy = Math.Min(decompressLeftovers, numBytes);
Array.Copy(decompressBuffer, decompressBufferOffset, sampleBuffer, offset, toCopy);
decompressLeftovers -= toCopy;
if (decompressLeftovers == 0)
{
decompressBufferOffset = 0;
}
else
{
decompressBufferOffset += toCopy;
}
bytesRead += toCopy;
offset += toCopy;
}
int targetTocIndex = tocIndex; // the frame index that contains the requested data
if (repositionedFlag)
{
decompressor.Reset();
// Seek back a few frames of the stream to get the reset decoder decode a few
// warm-up frames before reading the requested data. Without the warm-up phase,
// the first half of the frame after the reset is attenuated and does not resemble
// the data as it would be when reading sequentially from the beginning, because
// the decoder is missing the required overlap from the previous frame.
tocIndex = Math.Max(0, tocIndex - 3); // no warm-up at the beginning of the stream
mp3Stream.Position = tableOfContents[tocIndex].FilePosition;
repositionedFlag = false;
}
while (bytesRead < numBytes)
{
Mp3Frame frame = ReadNextFrame();
if (frame != null)
{
int decompressed = decompressor.DecompressFrame(frame, decompressBuffer, 0);
if (tocIndex <= targetTocIndex || decompressed == 0)
{
// The first frame after a reset usually does not immediately yield decoded samples.
// Because the next instructions will fail if a buffer offset is set and the frame
// decoding didn't return data, we skip the part.
// We skip the following instructions also after decoding a warm-up frame.
continue;
}
// Two special cases can happen here:
// 1. We are interested in the first frame of the stream, but need to read the second frame too
// for the decoder to return decoded data
// 2. We are interested in the second frame of the stream, but because reading the first frame
// as warm-up didn't yield any data (because the decoder needs two frames to return data), we
// get data from the first and second frame.
// This case needs special handling, and we have to purge the data of the first frame.
else if (tocIndex == targetTocIndex + 1 && decompressed == bytesPerDecodedFrame * 2)
{
// Purge the first frame's data
Array.Copy(decompressBuffer, bytesPerDecodedFrame, decompressBuffer, 0, bytesPerDecodedFrame);
decompressed = bytesPerDecodedFrame;
}
int toCopy = Math.Min(decompressed - decompressBufferOffset, numBytes - bytesRead);
Array.Copy(decompressBuffer, decompressBufferOffset, sampleBuffer, offset, toCopy);
if ((toCopy + decompressBufferOffset) < decompressed)
{
decompressBufferOffset = toCopy + decompressBufferOffset;
decompressLeftovers = decompressed - decompressBufferOffset;
}
else
{
// no lefovers
decompressBufferOffset = 0;
decompressLeftovers = 0;
}
offset += toCopy;
bytesRead += toCopy;
}
else
{
break;
}
}
}
Debug.Assert(bytesRead <= numBytes, "MP3 File Reader read too much");
position += bytesRead;
return(bytesRead);
}