1 files changed, 64 insertions, 0 deletions
diff --git a/apps/web/src/timeline/audio-display.ts b/apps/web/src/timeline/audio-display.ts
new file mode 100644
index 00000000..9958c472
--- /dev/null
+++ b/apps/web/src/timeline/audio-display.ts
@@ -0,0 +1,64 @@
+import { clampDb } from "./audio-state";
+import { VOLUME_DB_MAX, VOLUME_DB_MIN } from "./audio-constants";
+
+const SLIDER_CURVE_EXPONENT = 2;
+const MIN_DISPLAY_DB = -40;
+const WAVEFORM_BAR_EXPONENT = 1.5;
+const MIN_LINEAR_GAIN = 10 ** (VOLUME_DB_MIN / 20);
+const MAX_LINEAR_GAIN = 10 ** (VOLUME_DB_MAX / 20);
+const LINEAR_GAIN_RANGE = MAX_LINEAR_GAIN - MIN_LINEAR_GAIN;
+
+function getNormalizedGainFromDb({ db }: { db: number }): number {
+	const clampedDb = clampDb(db);
+	const linearGain = 10 ** (clampedDb / 20);
+	return (linearGain - MIN_LINEAR_GAIN) / LINEAR_GAIN_RANGE;
+}
+
+/**
+ * Maps the clip's volume setting to the line position. The curve is defined in
+ * linear gain space so dragging near 0 dB is precise while mute compresses into
+ * the bottom of the clip.
+ */
+export function getLinePosFromDb({ db }: { db: number }): number {
+	const normalizedGain = Math.max(
+		0,
+		Math.min(1, getNormalizedGainFromDb({ db })),
+	);
+	const progress = normalizedGain ** (1 / SLIDER_CURVE_EXPONENT);
+	return (1 - progress) * 100;
+}
+
+/**
+ * Inverse of getLinePosFromDb. Converts a drag position back into the clip's
+ * volume setting without depending on the underlying audio content.
+ */
+export function getDbFromLinePos({ percent }: { percent: number }): number {
+	const clampedPercent = Math.max(0, Math.min(100, percent));
+	const progress = 1 - clampedPercent / 100;
+	const normalizedGain = progress ** SLIDER_CURVE_EXPONENT;
+	const linearGain = MIN_LINEAR_GAIN + normalizedGain * LINEAR_GAIN_RANGE;
+	return clampDb(20 * Math.log10(linearGain));
+}
+
+/**
+ * Maps an output amplitude (raw sample amplitude × gain) to a visible waveform
+ * height fraction using a dB scale. Agnostic to whether the input is peak or
+ * RMS — the caller decides which measure feeds this function; the mapping
+ * curve is the same either way.
+ *
+ * The log scale keeps quiet content visible while reserving the top of the
+ * element for amplitudes that approach 0 dBFS.
+ */
+export function getBarFractionFromOutputAmplitude({
+	outputAmplitude,
+}: {
+	outputAmplitude: number;
+}): number {
+	if (outputAmplitude <= 0) return 0;
+	const db = 20 * Math.log10(outputAmplitude);
+	if (db <= MIN_DISPLAY_DB) return 0;
+	return Math.min(
+		1,
+		((db - MIN_DISPLAY_DB) / -MIN_DISPLAY_DB) ** WAVEFORM_BAR_EXPONENT,
+	);
+}