feat: add adaptive soundtrack mixer

tests/unit/soundtrack-transport.test.ts

@@ -1,11 +1,24 @@
 import { describe, expect, it } from 'vitest';
 import {
+  AFTERGLOW_LOOP_END_SAMPLE,
+  AFTERGLOW_LOOP_START_SAMPLE,
+  AFTERGLOW_TRANSITION_SECONDS,
+  DRIVE_LIFT_LOOP_SAMPLES,
+  DRIVE_LIFT_LOOP_SECONDS,
+  MAIN_DURATION_SAMPLES,
+  MAIN_DURATION_SECONDS,
   MAIN_PHRASE_BARS,
+  MUSIC_BAR_SAMPLES,
   MUSIC_BAR_SECONDS,
+  MUSIC_BEAT_SAMPLES,
+  MUSIC_BEAT_SECONDS,
   INTRO_IN_END_SECONDS,
   SOUNDTRACK_SAMPLE_RATE,
   mainPhraseOffsetSeconds,
+  nextBeatTime,
   nextSafeBarTime,
+  phaseAlignedLoopOffset,
+  resolveMainSchedule,
   resolveInitialPlayback,
 } from '@/audio/soundtrack-transport';
 
@@ -50,4 +63,44 @@ describe('soundtrack transport decisions', () => {
     );
     expect(earliestIntroExit).toBeCloseTo(anchorTime + MUSIC_BAR_SECONDS * 2, 8);
   });
+
+  it('pins the short adaptive regions to whole samples', () => {
+    expect(MUSIC_BEAT_SAMPLES).toBe(33_488);
+    expect(MUSIC_BAR_SAMPLES).toBe(133_953);
+    expect(DRIVE_LIFT_LOOP_SAMPLES).toBe(535_814);
+    expect(AFTERGLOW_LOOP_START_SAMPLE).toBe(133_953);
+    expect(AFTERGLOW_LOOP_END_SAMPLE).toBe(1_205_581);
+    expect(MAIN_DURATION_SAMPLES).toBe(8_573_023);
+  });
+
+  it('derives one immutable main anchor and the final-bar afterglow handoff', () => {
+    expect(resolveMainSchedule({
+      startTime: 10,
+      offsetSeconds: mainPhraseOffsetSeconds(6),
+      bufferDuration: MAIN_DURATION_SECONDS,
+    })).toEqual({
+      sourceStartTime: 10,
+      sourceOffsetSeconds: mainPhraseOffsetSeconds(6),
+      musicalAnchorTime: 10 - mainPhraseOffsetSeconds(6),
+      sourceEndTime: 10 + MAIN_DURATION_SECONDS - mainPhraseOffsetSeconds(6),
+      afterglowStartTime: 10 + MAIN_DURATION_SECONDS - mainPhraseOffsetSeconds(6) - AFTERGLOW_TRANSITION_SECONDS,
+    });
+  });
+
+  it('aligns a late loop source and sustained entry to the master beat', () => {
+    expect(phaseAlignedLoopOffset(13, 10, DRIVE_LIFT_LOOP_SECONDS))
+      .toBeCloseTo(3, 8);
+    expect(nextBeatTime(11.45, 10)).toBeCloseTo(
+      10 + 3 * MUSIC_BEAT_SECONDS,
+      8,
+    );
+  });
+
+  it('keeps one-sample-rounded beat and bar boundaries on the current boundary', () => {
+    const oneSample = 1 / SOUNDTRACK_SAMPLE_RATE;
+    expect(nextBeatTime(MUSIC_BEAT_SECONDS + oneSample, 0))
+      .toBeCloseTo(MUSIC_BEAT_SECONDS, 8);
+    expect(nextSafeBarTime(MUSIC_BAR_SECONDS + oneSample, 0, 0))
+      .toBeCloseTo(MUSIC_BAR_SECONDS, 8);
+  });
 });