initial public release.

2025-08-11 18:37:21 -07:00
commit de51967b49
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+/**
+ * MIDI file format constants for Standard MIDI File conversion
+ */
+
+// MIDI file header constants
+export const MIDI_HEADER = {
+  // Header chunk identifier
+  CHUNK_TYPE: new Uint8Array([0x4D, 0x54, 0x68, 0x64]), // "MThd"
+  
+  // Header chunk size (always 6 bytes)
+  HEADER_SIZE: new Uint8Array([0x00, 0x00, 0x00, 0x06]),
+  
+  // MIDI file formats
+  FORMAT_0: new Uint8Array([0x00, 0x00]), // Single track
+  FORMAT_1: new Uint8Array([0x00, 0x01]), // Multi-track, synchronous
+  FORMAT_2: new Uint8Array([0x00, 0x02]), // Multi-track, asynchronous
+};
+
+// Track chunk constants
+export const MIDI_TRACK = {
+  // Track chunk identifier
+  CHUNK_TYPE: new Uint8Array([0x4D, 0x54, 0x72, 0x6B]), // "MTrk"
+  
+  // End of track meta event
+  END_OF_TRACK: new Uint8Array([0x00, 0xFF, 0x2F, 0x00]),
+};
+
+// Timing constants
+export const MIDI_TIMING = {
+  // Ticks Per Quarter Note (TPQN) - 480 provides good resolution
+  TPQN: 480,
+  TPQN_BYTES: new Uint8Array([0x01, 0xE0]), // 480 in big-endian 16-bit
+};
+
+// MIDI event types
+export const MIDI_EVENTS = {
+  // Channel voice messages (status bytes)
+  NOTE_OFF: 0x80,
+  NOTE_ON: 0x90,
+  POLY_PRESSURE: 0xA0,
+  CONTROL_CHANGE: 0xB0,
+  PROGRAM_CHANGE: 0xC0,
+  CHANNEL_PRESSURE: 0xD0,
+  PITCH_BEND: 0xE0,
+  
+  // System exclusive
+  SYSEX: 0xF0,
+  
+  // Meta events
+  META_EVENT: 0xFF,
+  META_SEQUENCE_NUMBER: 0x00,
+  META_TEXT: 0x01,
+  META_COPYRIGHT: 0x02,
+  META_TRACK_NAME: 0x03,
+  META_INSTRUMENT_NAME: 0x04,
+  META_LYRIC: 0x05,
+  META_MARKER: 0x06,
+  META_CUE_POINT: 0x07,
+  META_CHANNEL_PREFIX: 0x20,
+  META_END_OF_TRACK: 0x2F,
+  META_TEMPO: 0x51,
+  META_SMPTE_OFFSET: 0x54,
+  META_TIME_SIGNATURE: 0x58,
+  META_KEY_SIGNATURE: 0x59,
+  META_SEQUENCER_SPECIFIC: 0x7F,
+};
+
+// MIDI channels (0-based)
+export const MIDI_CHANNELS = {
+  PIANO: 0,
+  GUITAR: 1,
+  BASS: 2,
+  DRUMS: 9, // Channel 10 (0-based = 9) is reserved for percussion
+};
+
+// General MIDI instrument program numbers (0-based)
+export const GM_INSTRUMENTS = {
+  PIANO: 0,        // Acoustic Grand Piano
+  GUITAR: 24,      // Acoustic Guitar (nylon)
+  BASS: 32,        // Acoustic Bass
+  DRUMS: 0,        // Not used for drums (uses channel 10)
+};
+
+// MIDI velocity constants
+export const MIDI_VELOCITY = {
+  MIN: 1,
+  MAX: 127,
+  DEFAULT: 64,
+};
+
+// MIDI note constants
+export const MIDI_NOTES = {
+  MIN: 0,
+  MAX: 127,
+  MIDDLE_C: 60, // C4
+};
+
+// Time signature constants
+export const MIDI_TIME_SIGNATURE = {
+  // Denominator values for MIDI (power of 2)
+  DENOMINATOR_MAP: {
+    2: 1,   // 2 = 2^1
+    4: 2,   // 4 = 2^2
+    8: 3,   // 8 = 2^3
+    16: 4,  // 16 = 2^4
+  } as const,
+  
+  // Default values
+  DEFAULT_METRONOME_PULSE: 24,  // MIDI clocks per quarter note
+  DEFAULT_32ND_NOTES_PER_QUARTER: 8,
+};
+
+// Key signature constants (for MIDI key signature meta event)
+export const MIDI_KEY_SIGNATURE = {
+  // Sharp keys (positive values)
+  SHARP_KEYS: {
+    'C major': 0,
+    'G major': 1,
+    'D major': 2,
+    'A major': 3,
+    'E major': 4,
+    'B major': 5,
+    'F# major': 6,
+    'C# major': 7,
+  },
+  
+  // Flat keys (negative values)
+  FLAT_KEYS: {
+    'F major': -1,
+    'Bb major': -2,
+    'Eb major': -3,
+    'Ab major': -4,
+    'Db major': -5,
+    'Gb major': -6,
+    'Cb major': -7,
+  },
+  
+  // Minor keys
+  MINOR_KEYS: {
+    'A minor': 0,
+    'E minor': 1,
+    'B minor': 2,
+    'F# minor': 3,
+    'C# minor': 4,
+    'G# minor': 5,
+    'D# minor': 6,
+    'A# minor': 7,
+    'D minor': -1,
+    'G minor': -2,
+    'C minor': -3,
+    'F minor': -4,
+    'Bb minor': -5,
+    'Eb minor': -6,
+    'Ab minor': -7,
+  },
+} as const;
+
+// Utility functions for MIDI data conversion
+export const MIDI_UTILS = {
+  /**
+   * Convert a 32-bit integer to big-endian byte array
+   */
+  int32ToBytes: (value: number): Uint8Array => {
+    return new Uint8Array([
+      (value >> 24) & 0xFF,
+      (value >> 16) & 0xFF,
+      (value >> 8) & 0xFF,
+      value & 0xFF,
+    ]);
+  },
+  
+  /**
+   * Convert a 16-bit integer to big-endian byte array
+   */
+  int16ToBytes: (value: number): Uint8Array => {
+    return new Uint8Array([
+      (value >> 8) & 0xFF,
+      value & 0xFF,
+    ]);
+  },
+  
+  /**
+   * Convert a variable-length quantity (VLQ) to bytes
+   * Used for MIDI delta times
+   */
+  encodeVLQ: (value: number): Uint8Array => {
+    const bytes: number[] = [];
+    
+    // Handle zero case
+    if (value === 0) {
+      return new Uint8Array([0]);
+    }
+    
+    // Convert to VLQ format
+    let temp = value & 0x7F;
+    while ((value >>= 7) > 0) {
+      temp <<= 8;
+      temp |= ((value & 0x7F) | 0x80);
+    }
+    
+    // Extract bytes
+    while (true) {
+      bytes.push(temp & 0xFF);
+      if (temp & 0x80) {
+        temp >>= 8;
+      } else {
+        break;
+      }
+    }
+    
+    return new Uint8Array(bytes);
+  },
+  
+  /**
+   * Calculate microseconds per quarter note from BPM
+   */
+  bpmToMicrosecondsPerQuarter: (bpm: number): number => {
+    return Math.round(60000000 / bpm);
+  },
+};