public MpegFrameHeader ReadFrameHeader()
{
byte[] header = new byte[10];
long frameStart = _input.Position;
while (header[0] != 0xFF)
{
frameStart = _input.Position;
int value = _input.ReadByte();
if (value == -1)
{
return(null);
}
header[0] = (byte)value;
}
_input.Read(header, 1, 9);
_input.Seek(frameStart, SeekOrigin.Begin);
MpegFrameHeader result = new MpegFrameHeader();
if (!ParseMpegFrameHeader(result, header))
{
throw new BinaryAssetBuilderException(ErrorCode.InvalidArgument, "Could not parse MP3 frame header.");
}
_input.Seek(result.HeaderSize, SeekOrigin.Current);
return(result);
}
private bool ParseMpegFrameHeader(MpegFrameHeader mpegFrameHeader, byte[] header)
{
BitStream bitStream = new BitStream(header);
if (bitStream.ReadUInt16(11) != 0x07FFu)
{
throw new BinaryAssetBuilderException(ErrorCode.InternalError, "MP3 sync bits do not match.");
}
mpegFrameHeader.Version = (MpegVersion)bitStream.ReadByte(2);
if (bitStream.ReadByte(2) != 0x01u)
{
throw new BinaryAssetBuilderException(ErrorCode.InternalError, "MP3 frame header error.");
}
mpegFrameHeader.HasCrc = bitStream.ReadBit();
mpegFrameHeader.BitrateIndex = bitStream.ReadByte(4);
mpegFrameHeader.SampleRateIndex = bitStream.ReadByte(2);
mpegFrameHeader.HasPadding = bitStream.ReadBit();
bitStream.ReadBit();
mpegFrameHeader.ChannelMode = (MpegChannelType)bitStream.ReadByte(2);
mpegFrameHeader.ModeExtension = bitStream.ReadByte(2);
mpegFrameHeader.HeaderSize = 4 + (mpegFrameHeader.HasCrc ? 2 : 0);
mpegFrameHeader.SampleRate = _sampleRateTable[(int)mpegFrameHeader.Version, mpegFrameHeader.SampleRateIndex];
switch (mpegFrameHeader.Version)
{
case MpegVersion.V1:
mpegFrameHeader.FrameSize = 144000 * _bitrateTable[(int)mpegFrameHeader.Version, mpegFrameHeader.BitrateIndex] / mpegFrameHeader.SampleRate;
break;
case MpegVersion.V2:
case MpegVersion.V2_5:
mpegFrameHeader.FrameSize = 144000 * _bitrateTable[(int)mpegFrameHeader.Version, mpegFrameHeader.BitrateIndex] / (mpegFrameHeader.SampleRate / 2);
break;
default:
throw new BinaryAssetBuilderException(ErrorCode.InternalError, "Bad MP3 version.");
}
if (mpegFrameHeader.HasPadding)
{
++mpegFrameHeader.FrameSize;
}
mpegFrameHeader.NumberOfChannels = mpegFrameHeader.ChannelMode == MpegChannelType.Mono ? 1 : 2;
return(true);
}
public MpegConverterSettings GetSettings()
{
MpegConverterSettings result = new MpegConverterSettings();
// at the moment we ignore everything but IsStreamed & channels anyway, we assume channels are same for every mp3 header
byte[] header = new byte[10];
long frameStart = _input.Position;
_input.Read(header, 0, 10);
_input.Seek(frameStart, SeekOrigin.Begin);
if (header[0] == 'I' && header[1] == 'D' && header[2] == '3')
{
SkipID3Tag(header);
}
while (header[0] != 0xFF)
{
frameStart = _input.Position;
int value = _input.ReadByte();
if (value == -1)
{
throw new BinaryAssetBuilderException(ErrorCode.InvalidArgument, "Could not find MP3 frame header.");
}
header[0] = (byte)value;
}
_input.Read(header, 1, 9);
_input.Seek(frameStart, SeekOrigin.Begin);
MpegFrameHeader frameHeader = new MpegFrameHeader();
if (!ParseMpegFrameHeader(frameHeader, header))
{
throw new BinaryAssetBuilderException(ErrorCode.InvalidArgument, "Could not parse MP3 frame header.");
}
result.NumberOfChannels = frameHeader.NumberOfChannels;
result.SampleRate = frameHeader.SampleRate;
return(result);
}
