/// <summary>
/// Reads a single <see cref="Chunk"/> from the file.
/// </summary>
/// <returns>The parsed <see cref="Chunk"/> -or- <see langword="null"/> if the end of the file has been reached.</returns>
/// <exception cref="IOException">An I/O error occurred.</exception>
/// <exception cref="SmfDecoderException">The file is corrupt and/or cannot be decoded due to a fatal error.</exception>
public Chunk ReadChunk()
{
var isEof = _source.BaseStream.Position >= _source.BaseStream.Length - 1;
if (_ntrks == 0)
{
if (isEof)
{
_logger?.Info(Strings.FinishedAtEnd, _source.BaseStream.Position);
}
else
{
_logger?.Warn(Strings.FinishedBeforeEnd, _source.BaseStream.Position);
}
return(null);
}
if (isEof)
{
var msg = string.Format(Strings.UnexpectedEofTracks, _ntrks);
_logger?.Fatal(msg, _source.BaseStream.Position);
throw new SmfDecoderException(msg, _source.BaseStream.Position);
}
// Read id and length
var id = Encoding.ASCII.GetString(_source.ReadBytes(4));
var len = MidiBytesConverter.ReadBigEndianUInt(_source.ReadBytes(4));
// Begin decoding the data by chunk type
switch (id)
{
case MidiHeader.HeaderIdentifier:
if (_ntrks > -1)
{
_logger?.Error(Strings.DuplicateHeader, _source.BaseStream.Position - 8);
}
var next = _source.BaseStream.Position + len;
// Read the values
var format = MidiBytesConverter.ReadBigEndianUShort(_source.ReadBytes(2));
_ntrks = MidiBytesConverter.ReadBigEndianUShort(_source.ReadBytes(2));
var div = MidiBytesConverter.ReadBigEndianShort(_source.ReadBytes(2));
// Jump to next chunk if case the header is longer than 6 for some reason
if (_source.BaseStream.Position < next)
{
_logger?.Warn(Strings.WrongLength, _source.BaseStream.Position - 10);
_source.BaseStream.Position = next;
}
// Create the header chunk object, taking in to account the time division method used
return(div < 0 ? new MidiHeader(format, (ushort)_ntrks, (sbyte)(div >> 8), (byte)(div & 0xFF)) : new MidiHeader(format, (ushort)_ntrks, div));
case MidiTrack.TrackIdentifier:
if (_ntrks == -1)
{
_logger?.Warn(Strings.NoHeader, _source.BaseStream.Position - 8);
}
// Read all the events in the track and return the track
return(new MidiTrack(ReadTrackEvents(len)));
default:
_logger?.Error(Strings.UnknownChunk, _source.BaseStream.Position - 8);
return(new UnknownChunk(id, _source.ReadBytes((int)len)));
}
}
private TrackEvent ReadTrackEvent()
{
var deltaTime = ReadVariableLengthEncoding();
// "Running Status": The last status byte is implied
var statusByte = _lastStatusByte;
var firstByte = _source.ReadByte();
// Check for new status byte
if ((firstByte & 0x80) == 1)
{
statusByte = firstByte;
firstByte = _source.ReadByte();
}
var statusUpper = statusByte >> 4;
// Save running status
if (statusUpper > 0x7 && statusUpper < 0xF)
{
_lastStatusByte = statusByte;
}
// Parse the event
var statusLower = (byte)(statusByte & 0xF);
MidiEvent ev = null;
switch (statusUpper)
{
case 0x8:
ev = new NoteOff(statusLower, firstByte, _source.ReadByte());
break;
case 0x9:
ev = new NoteOn(statusLower, firstByte, _source.ReadByte());
break;
case 0xA:
ev = new PolyphonicKeyPressure(statusLower, firstByte, _source.ReadByte());
break;
case 0xB:
if (firstByte < 120)
{
ev = new ControlChange(statusLower, firstByte, _source.ReadByte());
}
else
{
ev = new ChannelMode(statusLower, firstByte, _source.ReadByte());
}
break;
case 0xC:
ev = new ProgramChange(statusLower, firstByte);
break;
case 0xD:
ev = new ChannelPressure(statusLower, firstByte);
break;
case 0xE:
ev = new PitchBend(statusLower, firstByte, _source.ReadByte());
break;
case 0xF:
switch (statusLower)
{
case 0x0:
case 0x7:
ev = new SysEx(statusLower == 0, _source.ReadBytes(ReadVariableLengthEncoding(firstByte)));
break;
case 0xF:
var len = ReadVariableLengthEncoding();
var data = _source.ReadBytes(len);
switch (firstByte)
{
case 0x01:
case 0x02:
case 0x03:
case 0x04:
case 0x05:
case 0x06:
case 0x07:
case 0x08:
case 0x09:
case 0x0A:
case 0x0B:
case 0x0C:
case 0x0D:
case 0x0E:
case 0x0F:
ev = new TextEvent(Encoding.UTF8.GetString(data)); // TODO: Let user choose encoding
break;
case 0x20:
ev = new ChannelPrefix(data[0]);
break;
case 0x2F:
ev = new EndOfTrack();
break;
case 0x51:
ev = new SetTempo(MidiBytesConverter.ReadBigEndian24Bit(data));
break;
case 0x54:
ev = new SmpteOffset((byte)((data[0] >> 5) & 0x3), (byte)(data[0] & 0x1F), data[1], data[2], data[3], data[4]);
break;
case 0x58:
ev = new TimeSignature(data[0], data[1], data[2], data[3]);
break;
case 0x59:
ev = new KeySignature((sbyte)data[0], data[1] == 1);
break;
case 0x7F:
ev = new SequencerSpecificMetaEvent(data);
break;
default:
// TODO: Unrecognized metadata kind, non-fatal error
break;
}
break;
default:
// At this point, if the event was not recognized: FATAL ERROR!
throw new NotImplementedException();
}
break;
default:
// At this point, if the event was not recognized: FATAL ERROR!
throw new NotImplementedException();
}
return(new TrackEvent(deltaTime, ev));
}
