Inaccurate handling of .ttml / .tx3g subtitles in .mp4 container
VLC 3.0.20 opens TTML files and correctly displays them after opening these subtitles from a separate file. However, when embedded in an .mp4 container, the subtitles do not display after jumping forward or backward (Shift + Left or Right arrow). I use this command for muxing:
mp4box.exe -add "video.264#video:name=" -add "audio.aac#audio:group=1:name=" -add "TimedTextMarkupLanguage.ttml:hdlr=subt:stype=stpp:group=2:disable:name=" -itags reset -tmp tmp -new ttml.mp4
I made a test .mp4 file with such subtitles (ttml.mp4 and tx3g.mp4): https://github.com/zablockil/srt_vtt_mp4/tree/main/VLC