BabylonJS/Babylon.js · error · Error

Invalid frame count line

Error message

Invalid frame count line

What it means

The line following MOTION must be a frame-count declaration of the form 'Frames: <count>' — at least two whitespace-separated tokens. ReadBvh splits the line on whitespace and throws this error when fewer than 2 tokens are present, meaning the line exists but does not carry a frame count value (or the line is blank/garbage).

Source

Thrown at packages/dev/loaders/src/BVH/bvhLoader.ts:362

    const nodeLine = lines.shift();
    if (!nodeLine) {
        throw new Error("Unexpected end of file after HIERARCHY");
    }
    const root = ReadNode(lines, nodeLine.trim(), null, context);

    // read motion data
    const motionLine = lines.shift();
    if (!motionLine || motionLine.trim().toUpperCase() !== _MotionNode) {
        throw new Error("MOTION expected");
    }

    const framesLine = lines.shift();
    if (!framesLine) {
        throw new Error("Unexpected end of file before frame count");
    }
    const framesTokens = framesLine.trim().split(/[\s]+/);
    if (framesTokens.length < 2) {
        throw new Error("Invalid frame count line");
    }

    // number of frames
    const numFrames = parseInt(framesTokens[1]);
    if (isNaN(numFrames)) {
        throw new Error("Failed to read number of frames.");
    }
    context.numFrames = numFrames;

    // frame time
    const frameTimeLine = lines.shift();
    if (!frameTimeLine) {
        throw new Error("Unexpected end of file before frame time");
    }
    const frameTimeTokens = frameTimeLine.trim().split(/[\s]+/);
    if (frameTimeTokens.length < 3) {
        throw new Error("Invalid frame time line");
    }

View on GitHub (pinned to 0592b347b8)

Solutions

  1. Ensure the line right after MOTION reads exactly 'Frames: <integer>' (e.g. 'Frames: 120'); fix or re-export the file.
  2. Remove blank or stray lines between MOTION and the Frames line — the parser consumes lines positionally, not by scanning.
  3. If generating BVH in code, always emit `Frames: ${numFrames}` with the count on the same line.
  4. Check the file wasn't processed by a script that collapsed whitespace or dropped tokens; compare against a known-good BVH.
  5. Pre-validate with /MOTION\s*\n\s*Frames:\s+\d+/ before calling ReadBvh.

Example fix

// before
MOTION
Frames:
Frame Time: 0.033333

// after
MOTION
Frames: 120
Frame Time: 0.033333
Defensive patterns

Strategy: validation

Validate before calling

function parseFrameCount(text: string): number | null {
    const m = text.match(/MOTION\s*\n\s*Frames:\s*(\S+)/i);
    if (!m) return null;
    const n = parseInt(m[1], 10);
    return Number.isNaN(n) ? null : n;
}
const frameCount = parseFrameCount(bvhText);
if (frameCount === null) throw new Error("BVH 'Frames:' line is missing its numeric count");

Try / catch

try {
    const skeleton = ReadBvh(bvhText, scene, null, options);
} catch (e) {
    if (e instanceof Error && e.message === "Invalid frame count line") {
        console.error("Line after MOTION is not 'Frames: <n>'", e);
    } else {
        throw e;
    }
}

Prevention

When it happens

Trigger: Calling ReadBvh where the line after MOTION is 'Frames:' with no number, just a bare number like '120' without the 'Frames:' keyword plus a value counted... more precisely: a line such as 'Frames' (one token), an empty/whitespace-only line, or a stray line inserted between MOTION and the actual 'Frames:' line so the wrong line is parsed.

Common situations: Hand-edited BVH files where the count was deleted or the colon/number dropped, generators emitting 'MOTION' followed by a blank line instead of 'Frames: N', locale/tool variants writing 'Frames' without the count, or files where an extra blank-ish line shifted parsing.

Related errors

AI-assisted analysis of BabylonJS/Babylon.js@0592b347b8 (2026-08-30). Data as JSON: /api/errors/b6975c819392b2e5. Report an issue: GitHub.