/// <summary>Reads an MP3Frame from a stream</summary>
/// <remarks>http://mpgedit.org/mpgedit/mpeg_format/mpeghdr.htm has some good info
/// also see http://www.codeproject.com/KB/audio-video/mpegaudioinfo.aspx
/// </remarks>
/// <returns>A valid MP3 frame, or null if none found</returns>
public static Mp3Frame LoadFromStream(Stream input, bool readData)
{
var frame = new Mp3Frame();
frame.FileOffset = input.Position;
byte[] headerBytes = new byte[4];
int bytesRead = input.Read(headerBytes, 0, headerBytes.Length);
if (bytesRead < headerBytes.Length)
{
// reached end of stream, no more MP3 frames
return null;
}
while (!IsValidHeader(headerBytes, frame))
{
// shift down by one and try again
headerBytes[0] = headerBytes[1];
headerBytes[1] = headerBytes[2];
headerBytes[2] = headerBytes[3];
bytesRead = input.Read(headerBytes, 3, 1);
if (bytesRead < 1)
{
return null;
}
frame.FileOffset++;
}
/* no longer read the CRC since we include this in framelengthbytes
if (this.crcPresent)
this.crc = reader.ReadInt16();*/
int bytesRequired = frame.FrameLength - 4;
if (readData)
{
frame.RawData = new byte[frame.FrameLength];
Array.Copy(headerBytes, frame.RawData, 4);
bytesRead = input.Read(frame.RawData, 4, bytesRequired);
if (bytesRead < bytesRequired)
{
// TODO: could have an option to suppress this, although it does indicate a corrupt file
// for now, caller should handle this exception
throw new EndOfStreamException("Unexpected end of stream before frame complete");
}
}
else
{
// n.b. readData should not be false if input stream does not support seeking
input.Position += bytesRequired;
}
return frame;
}
/// <summary>
/// Decompresses a frame
/// </summary>
/// <param name="frame">The MP3 frame</param>
/// <param name="dest">destination buffer</param>
/// <param name="destOffset">Offset within destination buffer</param>
/// <returns>Bytes written into destination buffer</returns>
public int DecompressFrame(Mp3Frame frame, byte[] dest, int destOffset)
{
if (frame == null)
{
throw new ArgumentNullException("frame", "You must provide a non-null Mp3Frame to decompress");
}
Array.Copy(frame.RawData, conversionStream.SourceBuffer, frame.FrameLength);
int sourceBytesConverted = 0;
int converted = conversionStream.Convert(frame.FrameLength, out sourceBytesConverted);
if (sourceBytesConverted != frame.FrameLength)
{
throw new InvalidOperationException(String.Format("Couldn't convert the whole MP3 frame (converted {0}/{1})",
sourceBytesConverted, frame.FrameLength));
}
Array.Copy(conversionStream.DestBuffer, 0, dest, destOffset, converted);
return converted;
}
private void ValidateFrameFormat(Mp3Frame frame)
{
if (frame.SampleRate != Mp3WaveFormat.SampleRate)
{
string message =
String.Format(
"Got a frame at sample rate {0}, in an MP3 with sample rate {1}. Mp3FileReader does not support sample rate changes.",
frame.SampleRate, Mp3WaveFormat.SampleRate);
throw new InvalidOperationException(message);
}
int channels = frame.ChannelMode == ChannelMode.Mono ? 1 : 2;
if (channels != Mp3WaveFormat.Channels)
{
string message =
String.Format(
"Got a frame with channel mode {0}, in an MP3 with {1} channels. Mp3FileReader does not support changes to channel count.",
frame.ChannelMode, Mp3WaveFormat.Channels);
throw new InvalidOperationException(message);
}
}
/// <summary>
/// Opens MP3 from a stream rather than a file
/// Will not dispose of this stream itself
/// </summary>
/// <param name="inputStream">The incoming stream containing MP3 data</param>
/// <param name="frameDecompressorBuilder">Factory method to build a frame decompressor</param>
public Mp3FileReader(Stream inputStream, FrameDecompressorBuilder frameDecompressorBuilder)
{
if (inputStream == null)
{
throw new ArgumentNullException("inputStream");
}
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;
}
this.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;
this.mp3DataLength -= 128;
}
mp3Stream.Position = dataStartPosition;
// create a temporary MP3 format before we know the real bitrate
this.Mp3WaveFormat = new Mp3WaveFormat(firstFrame.SampleRate,
firstFrame.ChannelMode == ChannelMode.Mono ? 1 : 2, firstFrame.FrameLength, (int)bitRate);
CreateTableOfContents();
this.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
this.Mp3WaveFormat = new Mp3WaveFormat(firstFrame.SampleRate,
firstFrame.ChannelMode == ChannelMode.Mono ? 1 : 2, firstFrame.FrameLength, (int)bitRate);
decompressor = frameDecompressorBuilder(Mp3WaveFormat);
this.waveFormat = decompressor.OutputFormat;
this.bytesPerSample = (decompressor.OutputFormat.BitsPerSample) / 8 * decompressor.OutputFormat.Channels;
// no MP3 frames have more than 1152 samples in them
// some MP3s I seem to get double
this.decompressBuffer = new byte[1152 * bytesPerSample * 2];
}
catch (Exception)
{
if (ownInputStream)
{
inputStream.Dispose();
}
throw;
}
}
/// <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;
}
/// <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);
}
