func: static void input_callback(MMAL_PORT_T *port, MMAL_BUFFER_HEADER_T *buffer)
  
  {
  
      if (!buffer->cmd) {
  
          AVBufferRef *buf = buffer->user_data;
  
          av_buffer_unref(&buf);
  
      }
  
      mmal_buffer_header_release(buffer);
  
  }
  