/// <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); }