@remotion/renderer: More sound calculation to ensure even dimensions for H.264

[JonnyBurger]

No description provided.

[vercel]

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Project	Deployment	Preview	Comments	Updated (UTC)
bugs	Ready	Preview	Comment	Oct 5, 2025 0:32am
remotion	Ready	Preview	Comment	Oct 5, 2025 0:32am

[vercel]

The while loop algorithm can potentially produce zero or negative dimensions when the scale factor is small, which would result in invalid video dimensions.

View Details

📝 Patch Details

diff --git a/packages/renderer/src/validate-even-dimensions-with-codec.ts b/packages/renderer/src/validate-even-dimensions-with-codec.ts
index 55b27343ee..3043c6b7fe 100644
--- a/packages/renderer/src/validate-even-dimensions-with-codec.ts
+++ b/packages/renderer/src/validate-even-dimensions-with-codec.ts
@@ -39,14 +39,34 @@ export const validateEvenDimensionsWithCodec = ({
 	}
 
 	let heightEvenDimensions = height;
-	while (Math.round(heightEvenDimensions * scale) % 2 !== 0) {
+	while (Math.round(heightEvenDimensions * scale) % 2 !== 0 && heightEvenDimensions > 1) {
 		heightEvenDimensions--;
 	}
+	// If we can't find a dimension that produces an even scaled result, find the smallest that does
+	if (Math.round(heightEvenDimensions * scale) % 2 !== 0) {
+		// Search upward from 2 to find the first dimension that produces an even scaled result
+		for (let dim = 2; dim <= Math.max(height, 10); dim++) {
+			if (Math.round(dim * scale) % 2 === 0) {
+				heightEvenDimensions = dim;
+				break;
+			}
+		}
+	}
 
 	let widthEvenDimensions = width;
-	while (Math.round(widthEvenDimensions * scale) % 2 !== 0) {
+	while (Math.round(widthEvenDimensions * scale) % 2 !== 0 && widthEvenDimensions > 1) {
 		widthEvenDimensions--;
 	}
+	// If we can't find a dimension that produces an even scaled result, find the smallest that does
+	if (Math.round(widthEvenDimensions * scale) % 2 !== 0) {
+		// Search upward from 2 to find the first dimension that produces an even scaled result
+		for (let dim = 2; dim <= Math.max(width, 10); dim++) {
+			if (Math.round(dim * scale) % 2 === 0) {
+				widthEvenDimensions = dim;
+				break;
+			}
+		}
+	}
 
 	if (widthEvenDimensions !== width) {
 		Log.verbose(

Analysis

Algorithm can produce zero dimensions with small scale factors

What fails: validateEvenDimensionsWithCodec() in packages/renderer/src/validate-even-dimensions-with-codec.ts decrements dimensions without bounds checking, resulting in zero width or height when the scale factor is small

How to reproduce:

validateEvenDimensionsWithCodec({
  width: 1, height: 100, scale: 0.6, codec: 'h264', 
  wantsImageSequence: false, indent: false, logLevel: 'info'
})
// Returns: { actualWidth: 0, actualHeight: 100 }

Result: Zero width dimension returned, which would create invalid video files that cannot be encoded by H.264

Expected: All dimensions should remain above zero. Algorithm should find valid dimensions that produce even scaled results without going to zero, as confirmed by Stack Overflow documentation that H.264 requires even dimensions but has no documented minimum above zero.