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fix: guard getNativeAspectRatioValue against zero denominator #455

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fix: guard getNativeAspectRatioValue against zero denominator #455

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b8d05b0
fix: guard getNativeAspectRatioValue against zero denominator
Apr 16, 2026
271268e
refactor: unify 16/9 fallback literals with NATIVE_ASPECT_FALLBACK co…
shaun0927 Apr 16, 2026
5597651
test(aspectRatioUtils): exercise the crop-region branch with non-canc…
shaun0927 Apr 28, 2026
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67 changes: 67 additions & 0 deletions src/utils/aspectRatioUtils.test.ts
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Original file line number Diff line number Diff line change
@@ -0,0 +1,67 @@
import { describe, expect, it } from "vitest";
import { getNativeAspectRatioValue } from "./aspectRatioUtils";

const FALLBACK = 16 / 9;

describe("getNativeAspectRatioValue", () => {
it("returns the natural video ratio for a standard HD frame", () => {
expect(getNativeAspectRatioValue(1920, 1080)).toBeCloseTo(16 / 9);
});

it("applies the crop region when provided", () => {
// Use non-proportional crop dimensions so the ratio actually changes;
// equal width/height would cancel out and silently pass even if the
// crop were ignored.
const crop = { x: 0, y: 0, width: 0.75, height: 0.5 };
expect(getNativeAspectRatioValue(1920, 1080, crop)).toBeCloseTo((1920 * 0.75) / (1080 * 0.5));
});

it("falls back to 16/9 when video metadata is not yet loaded (height = 0)", () => {
expect(getNativeAspectRatioValue(1920, 0)).toBe(FALLBACK);
});

it("falls back to 16/9 when both dimensions are zero", () => {
expect(getNativeAspectRatioValue(0, 0)).toBe(FALLBACK);
});

it("falls back to 16/9 when the crop height collapses to zero", () => {
const crop = { x: 0, y: 0, width: 0.5, height: 0 };
expect(getNativeAspectRatioValue(1920, 1080, crop)).toBe(FALLBACK);
});

it("falls back to 16/9 when inputs are NaN", () => {
expect(getNativeAspectRatioValue(Number.NaN, 1080)).toBe(FALLBACK);
expect(getNativeAspectRatioValue(1920, Number.NaN)).toBe(FALLBACK);
});

it("falls back to 16/9 for non-positive dimensions", () => {
expect(getNativeAspectRatioValue(-1920, 1080)).toBe(FALLBACK);
expect(getNativeAspectRatioValue(1920, -1080)).toBe(FALLBACK);
});

it("never returns Infinity, NaN, or a non-positive ratio", () => {
const pathologicalInputs: Array<
[number, number, { x: number; y: number; width: number; height: number }?]
> = [
[0, 0],
[1920, 0],
[0, 1080],
[Number.POSITIVE_INFINITY, 1080],
[1920, Number.POSITIVE_INFINITY],
[Number.NaN, Number.NaN],
// Same idea, but exercising the crop-region branch so a future
// regression there can't slip past the dimension-only cases above.
[1920, 1080, { x: 0, y: 0, width: 0.5, height: 0 }],
[1920, 1080, { x: 0, y: 0, width: 0, height: 0.5 }],
[1920, 1080, { x: 0, y: 0, width: Number.NaN, height: 0.5 }],
[1920, 1080, { x: 0, y: 0, width: 0.5, height: Number.NaN }],
[1920, 1080, { x: 0, y: 0, width: Number.POSITIVE_INFINITY, height: 0.5 }],
[1920, 1080, { x: 0, y: 0, width: 0.5, height: -1 }],
];
for (const [w, h, crop] of pathologicalInputs) {
const ratio = getNativeAspectRatioValue(w, h, crop);
expect(Number.isFinite(ratio)).toBe(true);
expect(ratio).toBeGreaterThan(0);
}
Comment on lines +42 to +65
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@coderabbitai coderabbitai Bot Apr 28, 2026

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⚠️ Potential issue | 🟡 Minor

tighten the pathological-input assertion to enforce the actual contract.

right now (Line 63–64) you only assert “finite + positive”. that still allows incorrect positive values to pass. for these pathological cases, expected behavior is specifically fallback 16/9.

nit: stronger assertion (prevents sneaky regressions) 
  for (const [w, h, crop] of pathologicalInputs) {
    const ratio = getNativeAspectRatioValue(w, h, crop);
    expect(Number.isFinite(ratio)).toBe(true);
    expect(ratio).toBeGreaterThan(0);
+   expect(ratio).toBe(FALLBACK);
  }
🤖 Prompt for AI Agents 
Verify each finding against the current code and only fix it if needed.

In `@src/utils/aspectRatioUtils.test.ts` around lines 42 - 65, The test currently
only asserts finiteness and positivity for pathologicalInputs in the loop using
getNativeAspectRatioValue, which lets incorrect positive values slip through;
change the assertions for these specific cases to assert the exact fallback 16/9
behavior (e.g., replace the Number.isFinite and >0 checks with an assertion that
ratio equals the fallback 16/9, using a strict or numeric-precision matcher such
as toBeCloseTo if needed) so the pathological-input loop enforces the contract
that getNativeAspectRatioValue returns the 16/9 default for those inputs.

});
});
14 changes: 11 additions & 3 deletions src/utils/aspectRatioUtils.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,8 @@ export const ASPECT_RATIOS = [

export type AspectRatio = (typeof ASPECT_RATIOS)[number];

const NATIVE_ASPECT_FALLBACK = 16 / 9;

/**
* Returns the numeric value of an aspect ratio.
* For "native", returns a fallback ratio of 16/9.
Expand All @@ -33,7 +35,7 @@ export function getAspectRatioValue(aspectRatio: AspectRatio): number {
case "10:16":
return 10 / 16;
case "native":
return 16 / 9;
return NATIVE_ASPECT_FALLBACK;
default: {
const _exhaustiveCheck: never = aspectRatio;
return _exhaustiveCheck;
Expand All @@ -48,7 +50,13 @@ export function getNativeAspectRatioValue(
): number {
const cropW = cropRegion?.width ?? 1;
const cropH = cropRegion?.height ?? 1;
return (videoWidth * cropW) / (videoHeight * cropH);
const numerator = videoWidth * cropW;
const denominator = videoHeight * cropH;
if (!Number.isFinite(numerator) || !Number.isFinite(denominator) || denominator <= 0) {
return NATIVE_ASPECT_FALLBACK;
}
const ratio = numerator / denominator;
return ratio > 0 && Number.isFinite(ratio) ? ratio : NATIVE_ASPECT_FALLBACK;
}

export function getAspectRatioDimensions(
Expand All @@ -72,6 +80,6 @@ export function isPortraitAspectRatio(aspectRatio: AspectRatio): boolean {
}

export function formatAspectRatioForCSS(aspectRatio: AspectRatio, nativeRatio?: number): string {
if (aspectRatio === "native") return String(nativeRatio ?? 16 / 9);
if (aspectRatio === "native") return String(nativeRatio ?? NATIVE_ASPECT_FALLBACK);
return aspectRatio.replace(":", "/");
}
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