Video & Audio Editing MCP Server

Instructions

Implementation Reference

• server.py:1036-1101 (handler)

  The handler function for the 'change_video_speed' MCP tool. Adjusts video speed using setpts filter on video stream and chains multiple atempo filters on audio to support speed factors outside the single atempo limit (0.5-2.0). Handles input validation and ffmpeg errors with fallbacks.

  def change_video_speed(video_path: str, output_video_path: str, speed_factor: float) -> str:
      """Changes the playback speed of a video (and its audio).
  
      Args:
          video_path: Path to the input video file.
          output_video_path: Path to save the speed-adjusted video file.
          speed_factor: The factor by which to change the speed (e.g., 2.0 for 2x speed, 0.5 for half speed).
                        Must be positive.
      
      Returns:
          A status message indicating success or failure.
      """
      if speed_factor <= 0:
          return "Error: Speed factor must be positive."
      if not os.path.exists(video_path):
          return f"Error: Input video file not found at {video_path}"
  
      try:
          # Process atempo values (audio speed) - requires special handling for values outside 0.5-2.0 range
          atempo_value = speed_factor
          atempo_filters = []
          
          # Handle audio speed outside atempo's range (0.5-2.0)
          if speed_factor < 0.5:
              # For speed < 0.5, use multiple atempo=0.5 filters
              while atempo_value < 0.5:
                  atempo_filters.append("atempo=0.5")
                  atempo_value *= 2  # After applying atempo=0.5, the remaining factor doubles
              # Add the remaining factor if needed
              if atempo_value < 0.99:  # A bit of buffer for floating point comparison
                  atempo_filters.append(f"atempo={atempo_value}")
          elif speed_factor > 2.0:
              # For speed > 2.0, use multiple atempo=2.0 filters
              while atempo_value > 2.0:
                  atempo_filters.append("atempo=2.0")
                  atempo_value /= 2  # After applying atempo=2.0, the remaining factor halves
              # Add the remaining factor if needed
              if atempo_value > 1.01:  # A bit of buffer for floating point comparison
                  atempo_filters.append(f"atempo={atempo_value}")
          else:
              # For speed factors within range, just use one atempo filter
              atempo_filters.append(f"atempo={speed_factor}")
          
          # Apply separate filters to video and audio streams
          input_stream = ffmpeg.input(video_path)
          video = input_stream.video.setpts(f"{1.0/speed_factor}*PTS")
          
          # Chain multiple audio filters if needed
          audio = input_stream.audio
          for filter_str in atempo_filters:
              audio = audio.filter("atempo", speed_factor if filter_str == f"atempo={speed_factor}" else 
                                 0.5 if filter_str == "atempo=0.5" else 
                                 2.0 if filter_str == "atempo=2.0" else 
                                 float(filter_str.replace("atempo=", "")))
          
          # Combine processed streams and output
          output = ffmpeg.output(video, audio, output_video_path)
          output.run(capture_stdout=True, capture_stderr=True)
          
          return f"Video speed changed by factor {speed_factor} and saved to {output_video_path}"
      except ffmpeg.Error as e:
          error_message = e.stderr.decode('utf8') if e.stderr else str(e)
          return f"Error changing video speed: {error_message}"
      except Exception as e:
          return f"An unexpected error occurred while changing video speed: {str(e)}"