title: how to appending write audio frame use ffmpeg ？
body: <ul>
  <li>I found that ffmpeg has a concat protocol that can be used to splice/merge multiple audio files, but it has a param ouput file, that is, a new production to a target file; But I want to have a pattern added to the source file, just like the behavior of the fopen when mode = "a": Appends to a file. Writing operations. End of the file.</li>
  <li><p>Is there a direct way to do this?</p>
  
  <p>FILE *fopen (const char *filename, const char *mode)</p></li>
  </ul>