linux – How to use ffmpeg to extract the third data stream in mpegts

I’ve add a private text stream into the mpegts, as the third stream. Now I need get the stream payload with ffmpeg, I failed neither in command nor in code.

Input #0, mpegts, from 'input.ts':
  Duration: 00:03:28.78, start: 81831.351800, bitrate: 1115 kb/s
  Program 1
  Stream #0:0[0x1000]: Video: hevc ([36][0][0][0] / 0x0024), none, 15 fps, 15 tbr, 90k tbn, 90k tbc
  Stream #0:1[0x1001]: Audio: aac (LC) ([15][0][0][0] / 0x000F), mono, fltp, 71 kb/s
  Stream #0:2[0x1002]: Unknown: none ([128][0][0][0] / 0x0080)

Is it possible, that I modify the code in mpegts.c, to handle the Stream #0:2?
or just simply with a ffmpeg command?