Input #0, image2, from 'test_rand/11-small.png':
  Duration: 00:00:00.04, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: png, rgb24, 240x80, 25 tbr, 25 tbn, 25 tbc
Input #1, png_pipe, from 'test_rand/12-small.png':
  Duration: N/A, bitrate: N/A
    Stream #1:0: Video: png, rgb24, 240x80, 25 tbr, 25 tbn, 25 tbc
[NULL @ 0x7febf5001200] Requested output format 'raw' is not a suitable output format
pipe:1: Invalid argument