What causes "Error creating WebPAnimEncoder\n" in gohugoio/hugo?

Validate params.width and params.height are in [1, 16383] before entering the animated encode path; downscale or reject otherwise.

gohugoio/hugo · error

Error creating WebPAnimEncoder\n

Error message

Error creating WebPAnimEncoder\n

What it means

Printed by genwebp's encodeNRGBAAnimated (webp.c:211) when WebPAnimEncoderNew returns NULL. The animated encoder allocation fails for invalid canvas dimensions (over WebP's 16383 cap, or non-positive), or when libwebp cannot allocate the internal animation state. The function returns NULL and the Go host sees 'Error encoding NRGBA to WebP'.

Source

Thrown at internal/warpc/genwebp/webp.c:211

    if (!ok)
    {
        WebPMemoryWriterClear(&wrt);
        return NULL;
    }
    *output_size = wrt.size;
    return wrt.mem;
}

static uint8_t *encodeNRGBAAnimated(WebPConfig *config, InputParams params, const uint8_t *all_frames_data, size_t *output_size)
{
    WebPAnimEncoderOptions anim_options;
    WebPAnimEncoderOptionsInit(&anim_options);
    anim_options.anim_params.loop_count = params.loopCount;

    WebPAnimEncoder *enc = WebPAnimEncoderNew(params.width, params.height, &anim_options);
    if (enc == NULL)
    {
        fprintf(stderr, "Error creating WebPAnimEncoder\n");
        return NULL;
    }

    int timestamp = 0;
    size_t frame_rgba_size = (size_t)params.stride * params.height;

    for (int i = 0; i < params.frameCount; i++)
    {
        WebPPicture pic;
        if (!WebPPictureInit(&pic))
        {
            fprintf(stderr, "WebPPictureInit failed\n");
            WebPAnimEncoderDelete(enc);
            return NULL;
        }
        pic.use_argb = 1;
        pic.width = params.width;
        pic.height = params.height;

View on GitHub (pinned to 52c9bd7908)

Solutions

Validate params.width and params.height are in [1, 16383] before entering the animated encode path; downscale or reject otherwise.
Validate params.frameCount matches the actual number of frames supplied and is reasonable (< a few hundred) for the available memory.
If animating large canvases, raise the worker's memory limit or reduce frame resolution.
Prefer skipping the animated WebP output and falling back to a static resize for inputs that overflow the limit.
Log the params struct on the Go side at call time to correlate with this stderr line.

Example fix

// before: animated encode attempted on a 20000px-canvas GIF
encodeWebpAnimated(frames, 20000, 8000, durations)

// after: reject oversized canvas and fall back
if w > 16383 || h > 16383 {
    return fmt.Errorf("canvas %dx%d exceeds WebP limit; skipping animated WebP", w, h)
}
encodeWebpAnimated(frames, w, h, durations)

Defensive patterns

Strategy: validation

Validate before calling

func validateAnimParams(w, h, frameCount int) error {
    const max = 16383
    if w <= 0 || h <= 0 || w > max || h > max {
        return fmt.Errorf("canvas %dx%d out of range [1,%d]", w, h, max)
    }
    if frameCount <= 0 { return fmt.Errorf("frameCount %d must be > 0", frameCount) }
    return nil
}

Prevention

Reject or downscale canvases larger than 16383px on either edge.
Cap frameCount to what the worker's memory can hold.
For oversized inputs, fall back to a static encode instead of animated.
Log width/height/frameCount on the Go side to correlate with this stderr line.

When it happens

Trigger: Calling the animated path with params.width or params.height that exceed WebP limits or are <= 0, with an extremely high frameCount that exhausts memory during encoder construction, or under overall process memory pressure.

Common situations: Decoding a large animated source (GIF/animated WebP) whose canvas exceeds 16383px, decoding a GIF with hundreds of frames on a memory-constrained worker, or passing zero/negative dimensions because the params struct was not populated.

Related errors

AI-assisted analysis of gohugoio/hugo@52c9bd7908 (2026-08-09). Data as JSON: /api/errors/e72cfef71161e560. Report an issue: GitHub.