feat: dashcam photo mode with telemetry frame, lens drift and postcard capture

src/audio/music-pulse.ts

@@ -9,6 +9,7 @@ let audible = false;
 
 export function attachMusicPulse(node: AnalyserNode | null): void {
   analyser = node;
+  if (node === null) bus = null;
   bins = node === null ? null : new Uint8Array(new ArrayBuffer(node.frequencyBinCount));
 }
 
@@ -16,6 +17,13 @@ export function setMusicPulseAudible(value: boolean): void {
   audible = value;
 }
 
+/**
+ * DASHCAM: the mix bus (the tap after the mixer's sum, before the output
+ * gain), so a shutter click obeys mute and volume. Null unless audible.
+ */
+let bus: AudioNode | null = null;
+export const readSwitchboard = (): AudioNode | null => (audible ? bus : null);
+
 /** Bass energy in [0, 1]: the mean of roughly 90-380 Hz. */
 export function readMusicPulse(): number {
   if (!audible || analyser === null || bins === null) return 0;
@@ -37,5 +45,6 @@ export function createPulseTap(context: BaseAudioContext, destination: AudioNode
   } catch {
     attachMusicPulse(null);
   }
+  bus = tap;
   return tap;
 }

src/audio/switchboard-click.ts

@@ -0,0 +1,48 @@
+import { readSwitchboard } from '@/audio/music-pulse';
+
+/** Shutter click length, seconds. */
+export const SHUTTER_SECONDS = 0.03;
+/** The switchboard input's level on the mix bus. */
+export const SWITCHBOARD_GAIN = 0.18;
+
+/**
+ * DASHCAM's shutter: a ~30 ms burst of decaying noise with a fast gain
+ * envelope, through a switchboard input (gain 0.18) onto the mix bus, so
+ * mute and volume apply through the output gain. Lives in the lazy dashcam chunk. Plays only while
+ * the soundtrack is running and audible; never creates an AudioContext and
+ * never throws.
+ */
+export function playShutterClick(): boolean {
+  try {
+    const input = readSwitchboard();
+    if (input === null || input.context.state !== 'running') return false;
+    const context = input.context;
+    const length = Math.max(1, Math.round(context.sampleRate * SHUTTER_SECONDS));
+    const buffer = context.createBuffer(1, length, context.sampleRate);
+    const data = buffer.getChannelData(0);
+    // Two clicks a few ms apart (curtain open, curtain close) over decaying noise.
+    for (let i = 0; i < length; i += 1) {
+      const t = i / length;
+      const curtain = t > 0.55 && t < 0.62 ? 1.6 : 1;
+      data[i] = (Math.random() * 2 - 1) * (1 - t) ** 3 * curtain;
+    }
+    const source = context.createBufferSource();
+    source.buffer = buffer;
+    const envelope = context.createGain();
+    const start = context.currentTime + 0.005;
+    envelope.gain.setValueAtTime(0, start);
+    envelope.gain.linearRampToValueAtTime(SWITCHBOARD_GAIN, start + 0.002);
+    envelope.gain.exponentialRampToValueAtTime(0.0002, start + SHUTTER_SECONDS);
+    source.connect(envelope);
+    envelope.connect(input);
+    source.onended = () => {
+      source.disconnect();
+      envelope.disconnect();
+    };
+    source.start(start);
+    source.stop(start + SHUTTER_SECONDS + 0.01);
+    return true;
+  } catch {
+    return false;
+  }
+}