/// <summary>
/// checks if the four bytes represent a valid header,
/// if they are, will parse the values into Mp3Frame
/// </summary>
private static bool IsValidHeader(byte[] headerBytes, Mp3Frame frame)
{
if ((headerBytes[0] == 0xFF) && ((headerBytes[1] & 0xE0) == 0xE0))
{
// TODO: could do with a bitstream class here
frame.MpegVersion = (MpegVersion)((headerBytes[1] & 0x18) >> 3);
if (frame.MpegVersion == MpegVersion.Reserved)
{
//throw new FormatException("Unsupported MPEG Version");
return(false);
}
frame.MpegLayer = (MpegLayer)((headerBytes[1] & 0x06) >> 1);
if (frame.MpegLayer == MpegLayer.Reserved)
{
return(false);
}
int layerIndex = frame.MpegLayer == MpegLayer.Layer1 ? 0 : frame.MpegLayer == MpegLayer.Layer2 ? 1 : 2;
frame.CrcPresent = (headerBytes[1] & 0x01) == 0x00;
frame.BitRateIndex = (headerBytes[2] & 0xF0) >> 4;
if (frame.BitRateIndex == 15)
{
// invalid index
return(false);
}
int versionIndex = frame.MpegVersion == MpegVersion.Version1 ? 0 : 1;
frame.BitRate = bitRates[versionIndex, layerIndex, frame.BitRateIndex] * 1000;
if (frame.BitRate == 0)
{
return(false);
}
int sampleFrequencyIndex = (headerBytes[2] & 0x0C) >> 2;
if (sampleFrequencyIndex == 3)
{
return(false);
}
if (frame.MpegVersion == MpegVersion.Version1)
{
frame.SampleRate = sampleRatesVersion1[sampleFrequencyIndex];
}
else if (frame.MpegVersion == MpegVersion.Version2)
{
frame.SampleRate = sampleRatesVersion2[sampleFrequencyIndex];
}
else
{
// mpegVersion == MpegVersion.Version25
frame.SampleRate = sampleRatesVersion25[sampleFrequencyIndex];
}
bool padding = (headerBytes[2] & 0x02) == 0x02;
bool privateBit = (headerBytes[2] & 0x01) == 0x01;
frame.ChannelMode = (ChannelMode)((headerBytes[3] & 0xC0) >> 6);
frame.ChannelExtension = (headerBytes[3] & 0x30) >> 4;
if (frame.ChannelExtension != 0 && frame.ChannelMode != ChannelMode.JointStereo)
{
return(false);
}
frame.Copyright = (headerBytes[3] & 0x08) == 0x08;
bool original = (headerBytes[3] & 0x04) == 0x04;
int emphasis = (headerBytes[3] & 0x03);
int nPadding = padding ? 1 : 0;
frame.SampleCount = samplesPerFrame[versionIndex, layerIndex];
int coefficient = frame.SampleCount / 8;
if (frame.MpegLayer == MpegLayer.Layer1)
{
frame.FrameLength = (coefficient * frame.BitRate / frame.SampleRate + nPadding) * 4;
}
else
{
frame.FrameLength = (coefficient * frame.BitRate) / frame.SampleRate + nPadding;
}
if (frame.FrameLength > MaxFrameLength)
{
return(false);
}
return(true);
}
return(false);
}
/// <summary>
/// Reads decompressed PCM data from our MP3 file.
/// </summary>
public override int Read(Span <byte> sampleBuffer)
{
int bytesRead = 0;
var numBytes = sampleBuffer.Length; // the requested number of bytes
lock (repositionLock)
{
if (decompressLeftovers != 0)
{
int toCopy = Math.Min(decompressLeftovers, sampleBuffer.Length);
decompressBuffer.Slice(decompressBufferOffset, toCopy).Span.CopyTo(sampleBuffer);
decompressLeftovers -= toCopy;
if (decompressLeftovers == 0)
{
decompressBufferOffset = 0;
}
else
{
decompressBufferOffset += toCopy;
}
bytesRead += toCopy;
sampleBuffer = sampleBuffer.Slice(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(true); // internal read - should not advance position
if (frame != null)
{
int decompressed = decompressor.DecompressFrame(frame, decompressBuffer.Span);
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
decompressBuffer.Slice(bytesPerDecodedFrame, bytesPerDecodedFrame).CopyTo(decompressBuffer);
// question - why not just set decompressBufferOffset += bytesDecodedPerFrame here?
//Array.Copy(decompressBuffer, bytesPerDecodedFrame, decompressBuffer, 0, bytesPerDecodedFrame);
decompressed = bytesPerDecodedFrame;
}
int toCopy = Math.Min(decompressed - decompressBufferOffset, numBytes - bytesRead);
decompressBuffer.Slice(decompressBufferOffset, toCopy).Span.CopyTo(sampleBuffer);
//Array.Copy(decompressBuffer, decompressBufferOffset, sampleBuffer, offset, toCopy);
if ((toCopy + decompressBufferOffset) < decompressed)
{
decompressBufferOffset = toCopy + decompressBufferOffset;
decompressLeftovers = decompressed - decompressBufferOffset;
}
else
{
// no lefovers
decompressBufferOffset = 0;
decompressLeftovers = 0;
}
sampleBuffer = sampleBuffer.Slice(toCopy);
bytesRead += toCopy;
}
else
{
break;
}
}
}
Debug.Assert(bytesRead <= numBytes, "MP3 File Reader read too much");
position += bytesRead;
return(bytesRead);
}
private Mp3FileReader(Stream inputStream, FrameDecompressorBuilder frameDecompressorBuilder, bool ownInputStream)
{
if (inputStream == null)
{
throw new ArgumentNullException(nameof(inputStream));
}
if (frameDecompressorBuilder == null)
{
throw new ArgumentNullException(nameof(frameDecompressorBuilder));
}
this.ownInputStream = ownInputStream;
try
{
mp3Stream = inputStream;
Id3v2Tag = Id3v2Tag.ReadTag(mp3Stream);
dataStartPosition = mp3Stream.Position;
var firstFrame = Mp3Frame.LoadFromStream(mp3Stream);
if (firstFrame == null)
{
throw new InvalidDataException("Invalid MP3 file - no MP3 Frames Detected");
}
double bitRate = firstFrame.BitRate;
xingHeader = XingHeader.LoadXingHeader(firstFrame);
// If the header exists, we can skip over it when decoding the rest of the file
if (xingHeader != null)
{
dataStartPosition = mp3Stream.Position;
}
// workaround for a longstanding issue with some files failing to load
// because they report a spurious sample rate change
var secondFrame = Mp3Frame.LoadFromStream(mp3Stream);
if (secondFrame != null &&
(secondFrame.SampleRate != firstFrame.SampleRate ||
secondFrame.ChannelMode != firstFrame.ChannelMode))
{
// assume that the first frame was some kind of VBR/LAME header that we failed to recognise properly
dataStartPosition = secondFrame.FileOffset;
// forget about the first frame, the second one is the first one we really care about
firstFrame = secondFrame;
}
mp3DataLength = mp3Stream.Length - dataStartPosition;
// try for an ID3v1 tag as well
mp3Stream.Position = mp3Stream.Length - 128;
byte[] tag = new byte[128];
mp3Stream.Read(tag, 0, 128);
if (tag[0] == 'T' && tag[1] == 'A' && tag[2] == 'G')
{
Id3v1Tag = tag;
mp3DataLength -= 128;
}
mp3Stream.Position = dataStartPosition;
// create a temporary MP3 format before we know the real bitrate
Mp3WaveFormat = new Mp3WaveFormat(firstFrame.SampleRate,
firstFrame.ChannelMode == ChannelMode.Mono ? 1 : 2, firstFrame.FrameLength, (int)bitRate);
CreateTableOfContents();
tocIndex = 0;
// [Bit rate in Kilobits/sec] = [Length in kbits] / [time in seconds]
// = [Length in bits ] / [time in milliseconds]
// Note: in audio, 1 kilobit = 1000 bits.
// Calculated as a double to minimize rounding errors
bitRate = (mp3DataLength * 8.0 / TotalSeconds());
mp3Stream.Position = dataStartPosition;
// now we know the real bitrate we can create an accurate MP3 WaveFormat
Mp3WaveFormat = new Mp3WaveFormat(firstFrame.SampleRate,
firstFrame.ChannelMode == ChannelMode.Mono ? 1 : 2, firstFrame.FrameLength, (int)bitRate);
decompressor = frameDecompressorBuilder(Mp3WaveFormat);
waveFormat = decompressor.OutputFormat;
bytesPerSample = (decompressor.OutputFormat.BitsPerSample) / 8 * decompressor.OutputFormat.Channels;
// no MP3 frames have more than 1152 samples in them
bytesPerDecodedFrame = 1152 * bytesPerSample;
// some MP3s I seem to get double
decompressBuffer = new byte[bytesPerDecodedFrame * 2];
}
catch (Exception)
{
if (ownInputStream)
{
inputStream.Dispose();
}
throw;
}
}
/// <summary>
/// Load Xing Header
/// </summary>
/// <param name="frame">Frame</param>
/// <returns>Xing Header</returns>
public static XingHeader LoadXingHeader(Mp3Frame frame)
{
XingHeader xingHeader = new XingHeader();
xingHeader.frame = frame;
int offset = 0;
if (frame.MpegVersion == MpegVersion.Version1)
{
if (frame.ChannelMode != ChannelMode.Mono)
{
offset = 32 + 4;
}
else
{
offset = 17 + 4;
}
}
else if (frame.MpegVersion == MpegVersion.Version2)
{
if (frame.ChannelMode != ChannelMode.Mono)
{
offset = 17 + 4;
}
else
{
offset = 9 + 4;
}
}
else
{
return(null);
// throw new FormatException("Unsupported MPEG Version");
}
if ((frame.RawData[offset + 0] == 'X') &&
(frame.RawData[offset + 1] == 'i') &&
(frame.RawData[offset + 2] == 'n') &&
(frame.RawData[offset + 3] == 'g'))
{
xingHeader.startOffset = offset;
offset += 4;
}
else
{
return(null);
}
XingHeaderOptions flags = (XingHeaderOptions)ReadBigEndian(frame.RawData, offset);
offset += 4;
if ((flags & XingHeaderOptions.Frames) != 0)
{
xingHeader.framesOffset = offset;
offset += 4;
}
if ((flags & XingHeaderOptions.Bytes) != 0)
{
xingHeader.bytesOffset = offset;
offset += 4;
}
if ((flags & XingHeaderOptions.Toc) != 0)
{
xingHeader.tocOffset = offset;
offset += 100;
}
if ((flags & XingHeaderOptions.VbrScale) != 0)
{
xingHeader.vbrScale = ReadBigEndian(frame.RawData, offset);
offset += 4;
}
xingHeader.endOffset = offset;
return(xingHeader);
}
