def _format_subtitle(self, subtitle: str | Path | None) -> FileData | None:
        """
        Convert subtitle format to VTT and process the video to ensure it meets the HTML5 requirements.
        """

        def srt_to_vtt(srt_file_path, vtt_file_path):
            """Convert an SRT subtitle file to a VTT subtitle file"""
            with (
                open(srt_file_path, encoding="utf-8") as srt_file,
                open(vtt_file_path, "w", encoding="utf-8") as vtt_file,
            ):
                vtt_file.write("WEBVTT\n\n")
                for subtitle_block in srt_file.read().strip().split("\n\n"):
                    subtitle_lines = subtitle_block.split("\n")
                    subtitle_timing = subtitle_lines[1].replace(",", ".")
                    subtitle_text = "\n".join(subtitle_lines[2:])
                    vtt_file.write(f"{subtitle_timing} --> {subtitle_timing}\n")
                    vtt_file.write(f"{subtitle_text}\n\n")

        if subtitle is None:
            return None

        valid_extensions = (".srt", ".vtt")

        if Path(subtitle).suffix not in valid_extensions:
            raise ValueError(
                f"Invalid value for parameter `subtitle`: {subtitle}. Please choose a file with one of these extensions: {valid_extensions}"
            )

        # HTML5 only support vtt format
        if Path(subtitle).suffix == ".srt":
            temp_file = tempfile.NamedTemporaryFile(
                delete=False, suffix=".vtt", dir=self.GRADIO_CACHE
            )

            srt_to_vtt(subtitle, temp_file.name)
            subtitle = temp_file.name

        return FileData(path=str(subtitle))

        Convert subtitle format to VTT and process the video to ensure it meets the HTML5 requirements.
        
gradio/components/video.py