BabylonJS/Babylon.js · error · Error

Unexpected content format: ${contentFormat}

Error message

Unexpected content format: ${contentFormat}

What it means

Thrown while unpacking a glTF binary v1 container when the first chunk's contentFormat uint32 is not ContentFormat.JSON (0). glTF-Binary v1 requires the initial content chunk to be JSON.

Source

Thrown at packages/dev/loaders/src/glTF/glTFFileLoader.pure.ts:1307

                }
            }

            this._endPerformanceCounter("Unpack Binary");

            return unpacked;
        });
    }

    private _unpackBinaryV1Async(dataReader: DataReader, length: number): Promise<IGLTFLoaderData> {
        const ContentFormat = {
            JSON: 0,
        };

        const contentLength = dataReader.readUint32();
        const contentFormat = dataReader.readUint32();

        if (contentFormat !== ContentFormat.JSON) {
            throw new Error(`Unexpected content format: ${contentFormat}`);
        }

        const bodyLength = length - dataReader.byteOffset;

        const data: IGLTFLoaderData = { json: this._parseJson(dataReader.readString(contentLength)), bin: null };
        if (bodyLength !== 0) {
            const startByteOffset = dataReader.byteOffset;
            data.bin = {
                readAsync: (byteOffset, byteLength) => dataReader.buffer.readAsync(startByteOffset + byteOffset, byteLength),
                byteLength: bodyLength,
            };
        }

        return Promise.resolve(data);
    }

    private _unpackBinaryV2Async(dataReader: DataReader, length: number): Promise<IGLTFLoaderData> {
        const ChunkFormat = {

View on GitHub (pinned to 0592b347b8)

Solutions

  1. Convert the legacy .glb to glTF 2.0 (gltf-pipeline) so the modern v2 path is used
  2. Fix the chunk header so contentFormat is 0 (JSON)
  3. Re-export with a compliant tool and validate with glTF-Validator
Defensive patterns

Strategy: validation

Validate before calling

const dv = new DataView(await file.arrayBuffer());
if (dv.getUint32(0, true) !== 0x46546c67) throw new Error('not glb');
if (dv.getUint32(4, true) === 1) {
  const fmt = dv.getUint32(16, true);
  if (fmt !== 0) throw new Error('glb-v1 first chunk is not JSON: ' + fmt);
}

Try / catch

try {
  await loader.loadAsync(url);
} catch (e) {
  if (e.message?.startsWith('Unexpected content format')) {
    console.error('Legacy glb-v1 with non-JSON first chunk — convert to glTF 2.0:', e.message);
  }
}

Prevention

When it happens

Trigger: Loading a legacy glb-v1 file whose first chunk format field is wrong or corrupted.

Common situations: Very old exporter output; files hand-mangled or re-chunked by custom tooling; confusing v1 containers with v2 chunk layouts.

Related errors

AI-assisted analysis of BabylonJS/Babylon.js@0592b347b8 (2026-08-30). Data as JSON: /api/errors/ca65a0869aeb5c02. Report an issue: GitHub.