3 files changed, 67 insertions, 9 deletions

diff --git a/apps/web/src/lib/fps/__tests__/fps.test.ts b/apps/web/src/lib/fps/__tests__/fps.test.ts
index fd082bb2..10eed8d9 100644
--- a/apps/web/src/lib/fps/__tests__/fps.test.ts
+++ b/apps/web/src/lib/fps/__tests__/fps.test.ts
@@ -36,16 +36,16 @@ describe("getRaisedProjectFpsForImportedMedia", () => {
 	test("raises the project fps to match a higher-fps import", () => {
 		expect(
 			getRaisedProjectFpsForImportedMedia({
-				currentFps: 30,
+				currentFps: { numerator: 30, denominator: 1 },
 				importedAssets: [{ type: "video", fps: 60 }],
 			}),
-		).toBe(60);
+		).toEqual({ numerator: 60, denominator: 1 });
 	});
 
 	test("does not lower the project fps for lower-fps imports", () => {
 		expect(
 			getRaisedProjectFpsForImportedMedia({
-				currentFps: 60,
+				currentFps: { numerator: 60, denominator: 1 },
 				importedAssets: [{ type: "video", fps: 10 }],
 			}),
 		).toBeNull();
@@ -54,7 +54,7 @@ describe("getRaisedProjectFpsForImportedMedia", () => {
 	test("ignores non-video imports", () => {
 		expect(
 			getRaisedProjectFpsForImportedMedia({
-				currentFps: 30,
+				currentFps: { numerator: 30, denominator: 1 },
 				importedAssets: [
 					{ type: "image", fps: 60 },
 					{ type: "audio", fps: 120 },
diff --git a/apps/web/src/lib/fps/constants.ts b/apps/web/src/lib/fps/constants.ts
index 100c043a..30c3d2bc 100644
--- a/apps/web/src/lib/fps/constants.ts
+++ b/apps/web/src/lib/fps/constants.ts
@@ -1,3 +1,5 @@
+import type { FrameRate } from "opencut-wasm";
+
 export const FPS_PRESETS = [
 	{ value: "24", label: "24 fps" },
 	{ value: "25", label: "25 fps" },
@@ -6,4 +8,4 @@ export const FPS_PRESETS = [
 	{ value: "120", label: "120 fps" },
 ] as const;
 
-export const DEFAULT_FPS = 30;
+export const DEFAULT_FPS: FrameRate = { numerator: 30, denominator: 1 };
diff --git a/apps/web/src/lib/fps/utils.ts b/apps/web/src/lib/fps/utils.ts
index 8e3221a1..932788c4 100644
--- a/apps/web/src/lib/fps/utils.ts
+++ b/apps/web/src/lib/fps/utils.ts
@@ -1,7 +1,61 @@
+import type { FrameRate } from "opencut-wasm";
 import type { MediaAsset } from "@/lib/media/types";
 
 type MediaAssetFpsInput = Pick<MediaAsset, "type" | "fps">;
 
+const STANDARD_FRAME_RATES: Array<{ value: number; rate: FrameRate }> = [
+	{ value: 24_000 / 1_001, rate: { numerator: 24_000, denominator: 1_001 } },
+	{ value: 24, rate: { numerator: 24, denominator: 1 } },
+	{ value: 25, rate: { numerator: 25, denominator: 1 } },
+	{ value: 30_000 / 1_001, rate: { numerator: 30_000, denominator: 1_001 } },
+	{ value: 30, rate: { numerator: 30, denominator: 1 } },
+	{ value: 48, rate: { numerator: 48, denominator: 1 } },
+	{ value: 50, rate: { numerator: 50, denominator: 1 } },
+	{ value: 60_000 / 1_001, rate: { numerator: 60_000, denominator: 1_001 } },
+	{ value: 60, rate: { numerator: 60, denominator: 1 } },
+	{ value: 120, rate: { numerator: 120, denominator: 1 } },
+];
+
+const STANDARD_FRAME_RATE_TOLERANCE = 0.01;
+
+export function frameRateToFloat(rate: FrameRate): number {
+	return rate.numerator / rate.denominator;
+}
+
+export function frameRatesEqual(a: FrameRate, b: FrameRate): boolean {
+	return a.numerator === b.numerator && a.denominator === b.denominator;
+}
+
+export function floatToFrameRate(fps: number): FrameRate {
+	const standard = STANDARD_FRAME_RATES.find(
+		(candidate) => Math.abs(fps - candidate.value) <= STANDARD_FRAME_RATE_TOLERANCE,
+	);
+	if (standard) return standard.rate;
+
+	if (Number.isInteger(fps)) {
+		return { numerator: fps, denominator: 1 };
+	}
+
+	const ARBITRARY_DENOMINATOR = 1_000_000;
+	const scaledNumerator = Math.round(fps * ARBITRARY_DENOMINATOR);
+	const divisor = gcd(scaledNumerator, ARBITRARY_DENOMINATOR);
+	return {
+		numerator: scaledNumerator / divisor,
+		denominator: ARBITRARY_DENOMINATOR / divisor,
+	};
+}
+
+function gcd(left: number, right: number): number {
+	let a = Math.abs(left);
+	let b = Math.abs(right);
+	while (b !== 0) {
+		const remainder = a % b;
+		a = b;
+		b = remainder;
+	}
+	return a || 1;
+}
+
 export function getHighestImportedVideoFps({
 	mediaAssets,
 }: {
@@ -24,16 +78,18 @@ export function getRaisedProjectFpsForImportedMedia({
 	currentFps,
 	importedAssets,
 }: {
-	currentFps: number;
+	currentFps: FrameRate;
 	importedAssets: MediaAssetFpsInput[];
-}): number | null {
+}): FrameRate | null {
 	const highestImportedVideoFps = getHighestImportedVideoFps({
 		mediaAssets: importedAssets,
 	});
 
-	if (highestImportedVideoFps === null || highestImportedVideoFps <= currentFps) {
+	const currentFpsFloat = frameRateToFloat(currentFps);
+
+	if (highestImportedVideoFps === null || highestImportedVideoFps <= currentFpsFloat) {
 		return null;
 	}
 
-	return highestImportedVideoFps;
+	return floatToFrameRate(highestImportedVideoFps);
 }