/// <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 == Wave.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>
/// 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);
}
