remotion-dev/remotion · error · RemotionRenderingOutputError

Unexpected Lambda response format: {result_raw}

Error message

Unexpected Lambda response format: {result_raw}

What it means

Raised when the parsed Lambda response dict does NOT contain type === 'success' (and is not an errorMessage or type='error'). This is the catch-all for an unexpected response shape - the function returned something the client cannot interpret as success, controlled error, or runtime crash.

Source

Thrown at packages/lambda-python/remotion_lambda/remotionclient.py:509

            raise RemotionException(
                f"Failed to decode final Lambda response: {e}. Raw response: {result_raw}"
            ) from e
        except UnicodeDecodeError as e:
            raise RemotionException(
                f"Failed to decode Lambda response payload: {e}"
            ) from e

        if 'errorMessage' in decoded_result:
            raise RemotionRenderingOutputError(
                f"Lambda function returned an error: {decoded_result['errorMessage']}"
            )

        if 'type' in decoded_result and decoded_result['type'] == 'error':
            raise RemotionRenderingOutputError(
                f"Remotion rendering error: {decoded_result['message']}"
            )
        if 'type' not in decoded_result or decoded_result['type'] != 'success':
            raise RemotionRenderingOutputError(
                f"Unexpected Lambda response format: {result_raw}"
            )

        return decoded_result

    def _custom_serializer(self, obj: Any) -> Any: # Added type hints
        """A custom JSON serializer that handles enums and objects."""
        if isinstance(obj, Enum):
            return obj.value if hasattr(obj, 'value') else obj.name
        # Check if it's a dataclass instance before calling asdict
        # This often works better with mypy than just a try-except.
        if hasattr(obj, '__dataclass_fields__'):
            return asdict(obj)
        if hasattr(obj, '__dict__'):
            return obj.__dict__
        if hasattr(obj, '__iter__') and not isinstance(obj, (str, bytes, bytearray)):
            return list(obj)

View on GitHub (pinned to 78fe4bb3fd)

Solutions

1. Inspect the raw response text in the error message to understand what the function actually returned.
2. Verify the deployed Lambda function IS a Remotion render function and its version matches the Python client.
3. Confirm the function name in the client points to the right deployed function.
4. Re-deploy the function with `remotion lambda functions deploy` and update the client version to match.

Example fix

// before - calling a non-Remotion Lambda
client = RemotionClient(region=..., serve_url=..., function_name='my-other-function')
client.render_media(...)

# after
client = RemotionClient(
    region=...,
    serve_url=serve_url,
    function_name='remotion-render-remotionlambda-...-us-east-1',
)
client.render_media(...)

def assert_remotion_function(session, function_name: str) -> None:
    lam = session.client('lambda')
    tags = lam.list_tags(Resource=function_name).get('Tags', {})
    if tags.get('remotion:version') is None:
        raise ValueError(f'{function_name} does not look like a Remotion Lambda')

try:\n    result = client.render_media(...)\nexcept RemotionRenderingOutputError as e:\n    raw = str(e)  # contains raw response text\n    log.error('Unexpected Lambda response format. raw=%s', raw)\n    raise

When it happens

Trigger: Lambda returns a partial/empty dict, a chunk from a streaming progress event that was selected as the terminal result, or a response from an unrelated Lambda deployed to the same name. The raw response text is included for diagnosis.

Common situations: Version mismatch between the Python client and the deployed Remotion Lambda function; calling a non-Remotion Lambda by accident; selecting a progress chunk instead of the final chunk; truncated response leaving an empty dict.

Related errors

• Invalid JSON: ${JSON.stringify(decoded)}
• You have multiple buckets ({', '.join(buckets)}) in your S3
• Failed to parse Lambda response stream: {e}
• Failed to decode final Lambda response: {e}. Raw response: {
• Failed to decode Lambda response payload: {e}

AI-assisted analysis of remotion-dev/remotion@78fe4bb3fd (2026-08-12). Data as JSON: /api/errors/2f9cfcdafd4da1fe. Report an issue: GitHub.