How to mux .ttxt subtitle with ffmpeg?

[Selur]

I got an .ass, which I converted to ttxt.
Since using:

-add "G:\Output\test_0.ttxt":name="TEST_TITLE":lang="aa"

with MP4Box works, I think the .ttxt file is fine.

Problem is when I call ffmpeg with:

ffmpeg -y  -r 25/1 -i "J:\tmp\2023-06-18@07_43_36_4710__04.mkv" -i "G:\Output\test_0.ttxt" -vcodec copy -scodec copy -metadata:s:s:1 handler="TEST_TITLE" -metadata:s:s:1 language="aar" -metadata encoding_tool="Hybrid 2023.06.17.1" -map 0:0 -map 1:0  -aspect 640:352 -r 25/1 "G:\Output\test.mp4"

I get:

Input #0, matroska,webm, from 'J:\tmp\2023-06-18@07_43_36_4710__04.mkv':
  Metadata:
    encoder         : libebml v1.4.4 + libmatroska v1.7.1
    creation_time   : 2023-06-18T05:43:46.000000Z
  Duration: 00:00:17.16, start: 0.000000, bitrate: 427 kb/s
  Stream #0:0: Video: h264 (High), yuv420p(tv, bt470bg/unknown/unknown, progressive), 640x352 [SAR 1:1 DAR 20:11], 25 fps, 25 tbr, 1k tbn (default) (forced)
    Metadata:
      BPS             : 423490
      DURATION        : 00:00:17.160000000
      NUMBER_OF_FRAMES: 429
      NUMBER_OF_BYTES : 908387
      _STATISTICS_WRITING_APP: mkvmerge v76.0 ('Celebration') 64-bit
      _STATISTICS_WRITING_DATE_UTC: 2023-06-18 05:43:46
      _STATISTICS_TAGS: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
[in#1 @ 0000023364906bc0] Error opening input: Invalid data found when processing input

From the looks of it ffmpeg has a problem with the input file.
=> Does anyone know how to use FFmpeg to mux .ttxt subtitles?

Cu Selur

[richardpl]

XML based subtitles decoding/demuxing is not implemented

[Selur]

argh,.. so I would have to convert them to srt first.
Thanks for the info.