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56 lines
2.4 KiB
TypeScript
56 lines
2.4 KiB
TypeScript
/**
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* Even-dimension normalization for chroma-subsampled encodes.
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*
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* libx264 / libx265 with 4:2:0 chroma subsampling (yuv420p, yuv420p10le)
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* require both width and height to be even. An odd output dimension makes the
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* encoder abort before writing a single packet:
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*
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* [libx264] height not divisible by 2 (1080x723)
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* Error while opening encoder ... Invalid argument
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*
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* A composition with an odd data-width / data-height (e.g. a custom 3:1 canvas
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* at 1080x723) therefore fails to encode to H.264. The fix pads the odd
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* dimension up by a single pixel inside the encode filter chain, so the
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* encoder always receives even dimensions. Padding (not scaling) means content
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* is never resampled — at most one transparent/black row or column is added at
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* the bottom-right edge.
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*/
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// `pad=ceil(iw/2)*2:ceil(ih/2)*2` rounds each dimension UP to the next even
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// value (a no-op when already even) and keeps content at the top-left (x=0,y=0
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// default), so nothing shifts. iw/ih are evaluated by FFmpeg at runtime, so
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// this works whether or not the caller knows the frame size up front.
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const EVEN_DIMENSION_PAD = "pad=ceil(iw/2)*2:ceil(ih/2)*2";
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/**
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* Pixel formats whose chroma subsampling requires even width AND height.
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* 4:2:0 family only: yuv420p (H.264 SDR), yuv420p10le (H.265 HDR), and the
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* full-range yuvj420p Chrome screenshots arrive as. ProRes 4444
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* (yuva444p10le) and other 4:4:4 / alpha formats sample chroma per-pixel and
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* accept odd dimensions, so they are deliberately excluded — padding them
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* would needlessly distort transparent output.
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*/
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export function requiresEvenDimensions(pixelFormat: string): boolean {
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return pixelFormat.startsWith("yuv420") || pixelFormat.startsWith("yuvj420");
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}
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/**
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* Append the even-dimension pad to an FFmpeg `-vf` chain when the target pixel
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* format requires it. When both dimensions are known and already even, omit
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* the filter entirely so minimal FFmpeg builds do not need to provide `pad`.
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* Returns the chain unchanged for formats that accept odd dimensions, and
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* returns just the pad when there is no existing chain.
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*/
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export function withEvenDimensionPad(
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vfChain: string,
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pixelFormat: string,
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width?: number,
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height?: number,
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): string {
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if (!requiresEvenDimensions(pixelFormat)) return vfChain;
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if (width !== undefined && height !== undefined && width % 2 === 0 && height % 2 === 0) {
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return vfChain;
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}
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return vfChain ? `${vfChain},${EVEN_DIMENSION_PAD}` : EVEN_DIMENSION_PAD;
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}
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