Video & Audio Editing MCP Server

Instructions

Implementation Reference

• server.py:157-243 (handler)

  The main handler function for the 'change_aspect_ratio' tool. It uses FFmpeg to probe the video, calculate the target dimensions based on the desired aspect ratio, applies scaling, padding or cropping filters as specified, and outputs the processed video. Includes optimizations like codec copying where possible and fallbacks for re-encoding.

  @mcp.tool()
  def change_aspect_ratio(video_path: str, output_video_path: str, target_aspect_ratio: str, 
                            resize_mode: str = 'pad', padding_color: str = 'black') -> str:
      """Changes the aspect ratio of a video, using padding or cropping.
      Args listed in PRD.
      Returns:
          A status message indicating success or failure.
      """
      try:
          probe = ffmpeg.probe(video_path)
          video_stream_info = next((stream for stream in probe['streams'] if stream['codec_type'] == 'video'), None)
          if not video_stream_info:
              return "Error: No video stream found in the input file."
  
          original_width = int(video_stream_info['width'])
          original_height = int(video_stream_info['height'])
  
          num, den = map(int, target_aspect_ratio.split(':'))
          target_ar_val = num / den
          original_ar_val = original_width / original_height
  
          vf_filter = ""
          # Attempt to copy codecs if the operation doesn't strictly require re-encoding video stream
          # This is mostly for padding. Cropping implies re-encoding the video stream.
          codec_to_use = None 
  
          if resize_mode == 'pad':
              if abs(original_ar_val - target_ar_val) < 1e-4:
                  try:
                      ffmpeg.input(video_path).output(output_video_path, c='copy').run(capture_stdout=True, capture_stderr=True)
                      return f"Video aspect ratio already matches. Copied to {output_video_path}."
                  except ffmpeg.Error:
                       # If copy fails, just re-encode
                      ffmpeg.input(video_path).output(output_video_path).run(capture_stdout=True, capture_stderr=True)
                      return f"Video aspect ratio already matches. Re-encoded to {output_video_path}."
              
              if original_ar_val > target_ar_val: 
                  final_w = int(original_height * target_ar_val)
                  final_h = original_height
                  vf_filter = f"scale={final_w}:{final_h}:force_original_aspect_ratio=decrease,pad={final_w}:{final_h}:(ow-iw)/2:(oh-ih)/2:{padding_color}"
              else: 
                  final_w = original_width
                  final_h = int(original_width / target_ar_val)
                  vf_filter = f"scale={final_w}:{final_h}:force_original_aspect_ratio=decrease,pad={final_w}:{final_h}:(ow-iw)/2:(oh-ih)/2:{padding_color}"
              codec_to_use = 'copy' # Try to copy for padding, audio will be copied too
  
          elif resize_mode == 'crop':
              if abs(original_ar_val - target_ar_val) < 1e-4:
                  try:
                      ffmpeg.input(video_path).output(output_video_path, c='copy').run(capture_stdout=True, capture_stderr=True)
                      return f"Video aspect ratio already matches. Copied to {output_video_path}."
                  except ffmpeg.Error:
                      ffmpeg.input(video_path).output(output_video_path).run(capture_stdout=True, capture_stderr=True)
                      return f"Video aspect ratio already matches. Re-encoded to {output_video_path}."
              
              if original_ar_val > target_ar_val: 
                  new_width = int(original_height * target_ar_val)
                  vf_filter = f"crop={new_width}:{original_height}:(iw-{new_width})/2:0"
              else: 
                  new_height = int(original_width / target_ar_val)
                  vf_filter = f"crop={original_width}:{new_height}:0:(ih-{new_height})/2"
          else:
              return f"Error: Invalid resize_mode '{resize_mode}'. Must be 'pad' or 'crop'."
          
          try:
              # Try with specified video filter and copying audio codec
              ffmpeg.input(video_path).output(output_video_path, vf=vf_filter, acodec='copy').run(capture_stdout=True, capture_stderr=True)
              return f"Video aspect ratio changed (audio copy) to {target_aspect_ratio} using {resize_mode}. Saved to {output_video_path}"
          except ffmpeg.Error as e_acopy:
              # Fallback to re-encoding audio if audio copy failed
              try:
                  ffmpeg.input(video_path).output(output_video_path, vf=vf_filter).run(capture_stdout=True, capture_stderr=True)
                  return f"Video aspect ratio changed (audio re-encoded) to {target_aspect_ratio} using {resize_mode}. Saved to {output_video_path}"
              except ffmpeg.Error as e_recode_all:
                  err_acopy_msg = e_acopy.stderr.decode('utf8') if e_acopy.stderr else str(e_acopy)
                  err_recode_msg = e_recode_all.stderr.decode('utf8') if e_recode_all.stderr else str(e_recode_all)
                  return f"Error changing aspect ratio. Audio copy attempt failed: {err_acopy_msg}. Full re-encode attempt also failed: {err_recode_msg}."
  
      except ffmpeg.Error as e:
          error_message = e.stderr.decode('utf8') if e.stderr else str(e)
          return f"Error changing aspect ratio: {error_message}"
      except FileNotFoundError:
          return f"Error: Input video file not found at {video_path}"
      except ValueError:
          return f"Error: Invalid target_aspect_ratio format. Expected 'num:den' (e.g., '16:9')."
      except Exception as e:
          return f"An unexpected error occurred: {str(e)}"