internal XingHeader ReadXingHeader()
{
var result = new XingHeader();
var headerId = new string(ReadChars(4));
if (headerId != "Xing" && headerId != "Info")
{
return(result);
}
// The flags DWORD indicates whether the frame and byte counts are present:
uint flags = ReadUInt32BigEndian();
if ((flags & 0x1) == 1)
{
result.FrameCount = ReadUInt32BigEndian();
}
if ((flags >> 1 & 0x1) == 1)
{
result.ByteCount = ReadUInt32BigEndian();
}
return(result);
}
public AudioInfo ReadAudioInfo(Stream stream)
{
Contract.Ensures(Contract.Result <AudioInfo>() != null);
using (var reader = new FrameReader(stream))
{
// Seek to the first valid frame header:
FrameHeader frameHeader;
do
{
reader.SeekToNextFrame();
frameHeader = new FrameHeader(reader.ReadBytes(4));
} while (!reader.VerifyFrameSync(frameHeader));
if (frameHeader.Layer != "III")
{
throw new UnsupportedAudioException(string.Format(CultureInfo.InvariantCulture,
Resources.AudioInfoDecoderLayerError, frameHeader.Layer));
}
// Seek past the CRC, if present:
if (frameHeader.HasCrc)
{
reader.BaseStream.Seek(2, SeekOrigin.Current);
}
// Seek past the side information:
reader.BaseStream.Seek(GetSideInfoLength(frameHeader.ChannelMode, frameHeader.MpegVersion),
SeekOrigin.Current);
// Read the XING header (if present):
XingHeader xingHeader = reader.ReadXingHeader();
// If the byte count isn't present in the Xing header, use the file length:
if (xingHeader.ByteCount == 0)
{
xingHeader.ByteCount = (uint)reader.BaseStream.Length;
}
// Calculate the (approximate) sample count:
uint sampleCount = frameHeader.MpegVersion == "1"
? xingHeader.FrameCount * 1152
: xingHeader.FrameCount * 576;
// Calculate the bitrate from the VBR header, or use the information from the first frame:
int bitRate = sampleCount > 0
? CalculateBitRate(xingHeader.ByteCount, sampleCount, frameHeader.SampleRate)
: frameHeader.BitRate;
var format = new StringBuilder(bitRate.ToString(CultureInfo.CurrentCulture));
format.Append("kbps MPEG ");
format.Append(frameHeader.MpegVersion);
format.Append(" Layer ");
format.Append(frameHeader.Layer);
return(new AudioInfo(format.ToString(), frameHeader.ChannelMode == "Mono" ? 1 : 2, 0,
frameHeader.SampleRate, sampleCount));
}
}
