Initial OSS scaffold from Songs2VID (pre-strip)

lib/preview-typography.ts

@@ -0,0 +1,46 @@
+/**
+ * Shared typography math for dashboard preview ↔ FFmpeg output parity.
+ * Preview container uses a fixed reference width; scale from target encode resolution.
+ */
+
+import type { WatermarkFontKey } from "./fonts";
+import { CURATED_FONTS } from "./fonts";
+
+/** Matches LayoutStudio max preview width (tailwind max-w-xl ≈ 576px; use 576 for scaling). */
+export const PREVIEW_REFERENCE_WIDTH = 576;
+
+export function titleFontSizeForWidth(width: number): number {
+  return Math.max(22, Math.round(width * 0.032));
+}
+
+export function artistFontSizeForWidth(width: number): number {
+  return Math.max(16, Math.round(width * 0.02));
+}
+
+export function watermarkFontSizeForWidth(width: number): number {
+  return Math.max(22, Math.round(width * 0.028));
+}
+
+/** Scale encode-resolution px to preview container px. */
+export function scaleFontToPreview(fontPx: number, encodeWidth: number): number {
+  const ref = encodeWidth > 0 ? encodeWidth : 1280;
+  return Math.max(8, Math.round((fontPx * PREVIEW_REFERENCE_WIDTH) / ref));
+}
+
+export function previewFontFamilyCss(fontKey: WatermarkFontKey | undefined): string {
+  if (!fontKey || fontKey === "system") {
+    return "Arial, Helvetica, sans-serif";
+  }
+  if (fontKey === "custom") {
+    return "'S2VIDCustomWm', Arial, sans-serif";
+  }
+  const meta = CURATED_FONTS.find((f) => f.key === fontKey);
+  return meta ? `'S2VIDPreview-${meta.key}', Arial, sans-serif` : "Arial, sans-serif";
+}
+
+export function curatedFontApiUrl(key: string): string {
+  return `/api/fonts/${key}`;
+}
+
+/** Watermark overlay width as fraction of frame (matches encode.ts). */
+export const WATERMARK_WIDTH_FRACTION = 0.42;