BerriAI/litellm · error · ValueError

RunwayML TTS audio URL is not a string: {audio_url}

Error message

RunwayML TTS audio URL is not a string: {audio_url}

What it means

Type guard after RunwayML TTS polling: output contained an audio URL candidate, but it is not a string (e.g. a dict/object URL), so it cannot be used for the download request; the offending value is echoed.

Source

Thrown at litellm/llms/runwayml/text_to_speech/transformation.py:497

            task_id=task_id,
            api_base=self.DEFAULT_BASE_URL,
            headers=poll_headers,
            timeout_secs=RUNWAYML_POLLING_TIMEOUT,
        )

        # Get the completed task data
        task_data: Final = polled_response.json()

        verbose_logger.debug("RunwayML TTS polling complete, downloading audio")

        # Get audio URL from output
        output: Final = task_data.get("output", [])
        if not output or not isinstance(output, list) or len(output) == 0:
            raise ValueError("RunwayML TTS response missing audio URL in output")

        audio_url: Final = output[0]
        if not isinstance(audio_url, str):
            raise ValueError(f"RunwayML TTS audio URL is not a string: {audio_url}")

        # Download the audio file
        from litellm.llms.custom_httpx.http_handler import _get_httpx_client

        client: Final = _get_httpx_client()
        audio_response: Final = client.get(url=audio_url)
        audio_response.raise_for_status()

        verbose_logger.debug("RunwayML TTS audio downloaded successfully")

        # Return the audio data wrapped in HttpxBinaryResponseContent
        return HttpxBinaryResponseContent(audio_response)

    async def async_transform_text_to_speech_response(
        self,
        model: str,
        raw_response: httpx.Response,
        logging_obj: "LiteLLMLoggingObj",

View on GitHub (pinned to 77b7c6c40c)

Solutions

1. The audio URL field had an unexpected type; check the task output schema.
2. Report the schema mismatch to the litellm issue tracker.

Example fix

# inspect the audio_url value printed in the error.

When it happens

Trigger: Triggered when the RunwayML TTS audio URL in the output is not a string.

Common situations: See trigger scenarios.

AI-assisted analysis of BerriAI/litellm@77b7c6c40c (2026-08-18). Data as JSON: /api/errors/694c45b06c6943e9. Report an issue: GitHub.