/// <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 == 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> /// Reads decompressed PCM data from our MP3 file. /// </summary> public override int Read(Span <byte> sampleBuffer) { int bytesRead = 0; var numBytes = sampleBuffer.Length; // the requested number of bytes lock (repositionLock) { if (decompressLeftovers != 0) { int toCopy = Math.Min(decompressLeftovers, sampleBuffer.Length); decompressBuffer.Slice(decompressBufferOffset, toCopy).Span.CopyTo(sampleBuffer); decompressLeftovers -= toCopy; if (decompressLeftovers == 0) { decompressBufferOffset = 0; } else { decompressBufferOffset += toCopy; } bytesRead += toCopy; sampleBuffer = sampleBuffer.Slice(toCopy); } int targetTocIndex = tocIndex; // the frame index that contains the requested data if (repositionedFlag) { decompressor.Reset(); // Seek back a few frames of the stream to get the reset decoder decode a few // warm-up frames before reading the requested data. Without the warm-up phase, // the first half of the frame after the reset is attenuated and does not resemble // the data as it would be when reading sequentially from the beginning, because // the decoder is missing the required overlap from the previous frame. tocIndex = Math.Max(0, tocIndex - 3); // no warm-up at the beginning of the stream mp3Stream.Position = tableOfContents[tocIndex].FilePosition; repositionedFlag = false; } while (bytesRead < numBytes) { Mp3Frame frame = ReadNextFrame(true); // internal read - should not advance position if (frame != null) { int decompressed = decompressor.DecompressFrame(frame, decompressBuffer.Span); if (tocIndex <= targetTocIndex || decompressed == 0) { // The first frame after a reset usually does not immediately yield decoded samples. // Because the next instructions will fail if a buffer offset is set and the frame // decoding didn't return data, we skip the part. // We skip the following instructions also after decoding a warm-up frame. continue; } // Two special cases can happen here: // 1. We are interested in the first frame of the stream, but need to read the second frame too // for the decoder to return decoded data // 2. We are interested in the second frame of the stream, but because reading the first frame // as warm-up didn't yield any data (because the decoder needs two frames to return data), we // get data from the first and second frame. // This case needs special handling, and we have to purge the data of the first frame. else if (tocIndex == targetTocIndex + 1 && decompressed == bytesPerDecodedFrame * 2) { // Purge the first frame's data decompressBuffer.Slice(bytesPerDecodedFrame, bytesPerDecodedFrame).CopyTo(decompressBuffer); // question - why not just set decompressBufferOffset += bytesDecodedPerFrame here? //Array.Copy(decompressBuffer, bytesPerDecodedFrame, decompressBuffer, 0, bytesPerDecodedFrame); decompressed = bytesPerDecodedFrame; } int toCopy = Math.Min(decompressed - decompressBufferOffset, numBytes - bytesRead); decompressBuffer.Slice(decompressBufferOffset, toCopy).Span.CopyTo(sampleBuffer); //Array.Copy(decompressBuffer, decompressBufferOffset, sampleBuffer, offset, toCopy); if ((toCopy + decompressBufferOffset) < decompressed) { decompressBufferOffset = toCopy + decompressBufferOffset; decompressLeftovers = decompressed - decompressBufferOffset; } else { // no lefovers decompressBufferOffset = 0; decompressLeftovers = 0; } sampleBuffer = sampleBuffer.Slice(toCopy); bytesRead += toCopy; } else { break; } } } Debug.Assert(bytesRead <= numBytes, "MP3 File Reader read too much"); position += bytesRead; return(bytesRead); }
private Mp3FileReader(Stream inputStream, FrameDecompressorBuilder frameDecompressorBuilder, bool ownInputStream) { if (inputStream == null) { throw new ArgumentNullException(nameof(inputStream)); } if (frameDecompressorBuilder == null) { throw new ArgumentNullException(nameof(frameDecompressorBuilder)); } this.ownInputStream = ownInputStream; 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; } 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; mp3DataLength -= 128; } mp3Stream.Position = dataStartPosition; // create a temporary MP3 format before we know the real bitrate Mp3WaveFormat = new Mp3WaveFormat(firstFrame.SampleRate, firstFrame.ChannelMode == ChannelMode.Mono ? 1 : 2, firstFrame.FrameLength, (int)bitRate); CreateTableOfContents(); 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 Mp3WaveFormat = new Mp3WaveFormat(firstFrame.SampleRate, firstFrame.ChannelMode == ChannelMode.Mono ? 1 : 2, firstFrame.FrameLength, (int)bitRate); decompressor = frameDecompressorBuilder(Mp3WaveFormat); waveFormat = decompressor.OutputFormat; bytesPerSample = (decompressor.OutputFormat.BitsPerSample) / 8 * decompressor.OutputFormat.Channels; // no MP3 frames have more than 1152 samples in them bytesPerDecodedFrame = 1152 * bytesPerSample; // some MP3s I seem to get double decompressBuffer = new byte[bytesPerDecodedFrame * 2]; } catch (Exception) { if (ownInputStream) { inputStream.Dispose(); } throw; } }
/// <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); }