fix stream multiplaction

src/utils/audio-stream-reader.ts

@@ -15,26 +15,31 @@ const SAMPLE_RATE = 44100
 const CHANNELS = 1
 const BYTES_PER_SAMPLE = 2 // s16le
 
-/** How many samples to buffer (≈1 second) */
+/** How many samples to buffer (~1 second) */
 const RING_BUFFER_SAMPLES = SAMPLE_RATE
 
 export interface AudioStreamReaderOptions {
   /** Audio URL or file path to decode */
   url: string
-  /** Start position in seconds (for seeking sync) */
-  startPosition?: number
   /** Sample rate (default: 44100) */
   sampleRate?: number
 }
 
+/**
+ * Monotonically increasing generation counter.
+ * Each start() increments this; the read loop checks it to know
+ * if it's been superseded and should bail out.
+ */
+let globalGeneration = 0
+
 export class AudioStreamReader {
   private proc: ReturnType<typeof Bun.spawn> | null = null
   private ringBuffer: Float64Array
   private writePos = 0
   private totalSamplesWritten = 0
   private _running = false
-  private readPromise: Promise<void> | null = null
-  private url: string
+  private generation = 0
+  readonly url: string
   private sampleRate: number
 
   constructor(options: AudioStreamReaderOptions) {
@@ -55,14 +60,28 @@ export class AudioStreamReader {
 
   /**
    * Start the ffmpeg decode process and begin reading PCM data.
+   *
+   * If already running, the previous process is killed first.
+   * Uses a generation counter to guarantee that only one read loop
+   * is ever active — stale loops from killed processes bail out
+   * immediately.
+   *
    * @param startPosition Seek position in seconds (default: 0).
+   * @param speed Playback speed multiplier (default: 1). Applies ffmpeg
+   *              atempo filter so visualization stays in sync with audio.
    */
-  start(startPosition = 0): void {
-    if (this._running) return
+  start(startPosition = 0, speed = 1): void {
+    // Always kill the previous process first — no early return on _running
+    this.killProcess()
+
     if (!Bun.which("ffmpeg")) {
       throw new Error("ffmpeg not found — required for audio visualization")
     }
 
+    // Increment generation so any lingering read loop from a previous
+    // start() will see a mismatch and exit.
+    this.generation = ++globalGeneration
+
     const args = [
       "ffmpeg",
       "-loglevel", "quiet",
@@ -73,13 +92,21 @@ export class AudioStreamReader {
       args.push("-ss", String(startPosition))
     }
 
+    args.push("-i", this.url)
+
+    // Apply speed via atempo filter if not 1x.
+    // ffmpeg atempo only supports 0.5–100.0; chain multiple for extremes.
+    if (speed !== 1 && speed > 0) {
+      const atempoFilters = buildAtempoChain(speed)
+      args.push("-af", atempoFilters)
+    }
+
     args.push(
-      "-i", this.url,
       "-ac", String(CHANNELS),
       "-ar", String(this.sampleRate),
-      "-f", "s16le",       // raw signed 16-bit little-endian PCM
+      "-f", "s16le",
       "-acodec", "pcm_s16le",
-      "-",                 // output to stdout
+      "-",
     )
 
     this.proc = Bun.spawn(args, {
@@ -92,14 +119,22 @@ export class AudioStreamReader {
     this.writePos = 0
     this.totalSamplesWritten = 0
 
+    // Capture generation for this run
+    const myGeneration = this.generation
+
     // Start async reading loop
-    this.readPromise = this.readLoop()
+    this.readLoop(myGeneration)
 
     // Detect process exit
     this.proc.exited.then(() => {
-      this._running = false
+      // Only clear _running if this is still the current generation
+      if (this.generation === myGeneration) {
+        this._running = false
+      }
     }).catch(() => {
-      this._running = false
+      if (this.generation === myGeneration) {
+        this._running = false
+      }
     })
   }
 
@@ -107,7 +142,7 @@ export class AudioStreamReader {
    * Read available samples into the provided buffer.
    * Returns the number of samples actually copied.
    *
-   * @param out - Float64Array to fill with samples (scaled ~±32768 for cavacore).
+   * @param out - Float64Array to fill with samples (scaled ~+/-32768 for cavacore).
    * @returns Number of samples written to `out`.
    */
   read(out: Float64Array): number {
@@ -118,10 +153,8 @@ export class AudioStreamReader {
     const readStart = (this.writePos - available + this.ringBuffer.length) % this.ringBuffer.length
 
     if (readStart + available <= this.ringBuffer.length) {
-      // Contiguous read
       out.set(this.ringBuffer.subarray(readStart, readStart + available))
     } else {
-      // Wraps around
       const firstChunk = this.ringBuffer.length - readStart
       out.set(this.ringBuffer.subarray(readStart, this.ringBuffer.length))
       out.set(this.ringBuffer.subarray(0, available - firstChunk), firstChunk)
@@ -132,40 +165,44 @@ export class AudioStreamReader {
 
   /**
    * Stop the ffmpeg process and clean up.
-   * Safe to call multiple times.
+   * Safe to call multiple times. Guarantees the read loop exits.
    */
   stop(): void {
+    // Bump generation to invalidate any running read loop
+    this.generation = ++globalGeneration
     this._running = false
-    if (this.proc) {
-      try { this.proc.kill() } catch { /* ignore */ }
-      this.proc = null
-    }
+    this.killProcess()
     this.writePos = 0
     this.totalSamplesWritten = 0
   }
 
   /**
-   * Restart the reader at a new position (e.g. after a seek).
+   * Restart the reader at a new position and/or speed.
    */
-  restart(startPosition = 0): void {
-    this.stop()
-    this.start(startPosition)
+  restart(startPosition = 0, speed = 1): void {
+    this.start(startPosition, speed)
+  }
+
+  /** Kill the ffmpeg process without touching generation/state. */
+  private killProcess(): void {
+    if (this.proc) {
+      try { this.proc.kill() } catch { /* ignore */ }
+      this.proc = null
+    }
   }
 
   /** Internal: continuously reads stdout from ffmpeg and fills the ring buffer. */
-  private async readLoop(): Promise<void> {
+  private async readLoop(myGeneration: number): Promise<void> {
     const stdout = this.proc?.stdout
     if (!stdout || typeof stdout === "number") return
 
     const reader = (stdout as ReadableStream<Uint8Array>).getReader()
     try {
-      while (this._running) {
+      while (this.generation === myGeneration) {
         const { done, value } = await reader.read()
-        if (done || !this._running) break
+        if (done || this.generation !== myGeneration) break
         if (!value || value.byteLength === 0) continue
 
-        // Convert raw s16le bytes → Float64Array scaled for cavacore
-        // Ensure we have an even number of bytes (each sample = 2 bytes)
         const sampleCount = Math.floor(value.byteLength / BYTES_PER_SAMPLE)
         if (sampleCount === 0) continue
 
@@ -175,9 +212,8 @@ export class AudioStreamReader {
           sampleCount,
         )
 
-        // Write samples into ring buffer (as doubles, preserving int16 scale)
         for (let i = 0; i < sampleCount; i++) {
-          this.ringBuffer[this.writePos] = int16View[i] // ±32768 range
+          this.ringBuffer[this.writePos] = int16View[i]
           this.writePos = (this.writePos + 1) % this.ringBuffer.length
           this.totalSamplesWritten++
         }
@@ -189,3 +225,25 @@ export class AudioStreamReader {
     }
   }
 }
+
+/**
+ * Build an ffmpeg atempo filter chain for a given speed.
+ * atempo only accepts values in [0.5, 100.0], so we chain
+ * multiple filters for extreme values (e.g. 0.25 = atempo=0.5,atempo=0.5).
+ */
+function buildAtempoChain(speed: number): string {
+  const parts: string[] = []
+  let remaining = Math.max(0.25, Math.min(4, speed))
+
+  while (remaining > 100) {
+    parts.push("atempo=100.0")
+    remaining /= 100
+  }
+  while (remaining < 0.5) {
+    parts.push("atempo=0.5")
+    remaining /= 0.5
+  }
+  parts.push(`atempo=${remaining}`)
+
+  return parts.join(",")
+}