remotion-dev/remotion · error · RemotionInvalidArgumentException

Failed to serialize render parameters to JSON: {e}

Error message

Failed to serialize render parameters to JSON: {e}

What it means

Thrown by construct_render_request when json.dumps of the full serialized render payload (render_params.serialize_params()) raises TypeError or OverflowError, even after the custom serializer that handles enums, dataclasses, __dict__ and iterables. This means the payload still contained something the custom serializer could not represent (e.g. circular references, very deeply nested integers, or a type the custom serializer falls through on like a custom __dict__ containing non-serializable values).

Source

Thrown at packages/lambda-python/remotion_lambda/remotionclient.py:565

        render_params.serve_url = self.serve_url

        try:
            # Assuming RenderMediaParams and RenderStillParams both have an input_props attribute
            # and a private_serialized_input_props attribute (even if Optional)
            render_params.private_serialized_input_props = self._serialize_input_props(
                input_props=render_params.input_props, render_type=render_type
            )
        except (RemotionInvalidArgumentException, ClientError) as e:
            raise RemotionInvalidArgumentException(
                f"Failed to serialize input properties for rendering: {e}"
            ) from e

        # Ensure serialize_params method in models.py is typed to return Dict[str, Any]
        payload: Dict[str, Any] = render_params.serialize_params()
        try:
            return json.dumps(payload, default=self._custom_serializer)
        except (TypeError, OverflowError) as e:
            raise RemotionInvalidArgumentException(
                f"Failed to serialize render parameters to JSON: {e}"
            ) from e

    def construct_render_progress_request(
        self,
        render_id: str,
        bucket_name: str,
        log_level: str = "info", # Added type hint
        s3_output_provider: Optional[CustomCredentials] = None,
    ) -> str:
        """
        Construct a render progress request in JSON format.

        Args:
            render_id (str): ID of the render.
            bucket_name (str): Name of the bucket.
            log_level (str): Log level ("error", "warning", "info", "verbose").
            s3_output_provider (Optional[CustomCredentials]): Custom S3 credentials.

View on GitHub (pinned to 78fe4bb3fd)

Solutions

1. Read the wrapped TypeError/OverflowError message to identify the offending value or recursion depth.
2. Ensure every field set on RenderMediaParams/RenderStillParams reduces to JSON primitives or already-serialized dicts before calling render_media_on_lambda/render_still_on_lambda.
3. If using custom classes, convert them with to_dict() or dataclasses.asdict() yourself before assigning.
4. For OverflowError on large numbers, cap or stringify the value.

Example fix

// before
render_params.webhook = MyCustomWebhook()  # __dict__ holds a file handle
// after
render_params.webhook = Webhook(url='https://example.com/hook', secret='...')

import json
def payload_serializes(params_dict):
    try:
        json.dumps(params_dict, default=str)
        return True
    except (TypeError, OverflowError):
        return False

if not payload_serializes(render_params.serialize_params()):
    raise ValueError('render params contain non-serializable fields')

from enum import Enum
def serializable_value(v):
    if isinstance(v, Enum): return True
    if hasattr(v, '__dataclass_fields__'): return True
    return v is None or isinstance(v, (str, int, float, bool, list, dict))

from remotion_lambda.exceptions import RemotionInvalidArgumentException
try:
    json_str = client.construct_render_request(render_params, render_type='video-or-audio')
except RemotionInvalidArgumentException as e:
    logger.exception('Render request serialization failed; payload was: %r', render_params.serialize_params())
    raise

When it happens

Trigger: A render_params field whose value has a __dict__ that recursively references non-serializable objects; a numeric value so large that json.dumps raises OverflowError; a custom object that is not an Enum, dataclass, or iterable, and whose __dict__ still contains unsupported types.

Common situations: Attaching custom nested objects to optional params (e.g. webhook config with arbitrary objects); passing very large integers from compute-heavy props; mutating render_params after construction to inject non-serializable state.

Related errors

• Error serializing InputProps. Check for circular references
• Failed to serialize progress parameters to JSON: {e}
• Failed to parse Lambda response stream: {e}
• Failed to decode final Lambda response: {e}. Raw response: {
• Object of type {obj.__class__.__name__} is not JSON serializ

AI-assisted analysis of remotion-dev/remotion@78fe4bb3fd (2026-08-12). Data as JSON: /api/errors/a7b16256862e9a4e. Report an issue: GitHub.