[HELP] after encoding ass into mp4, but there is no subtitle at all

[Selur]

General side notes for improvement:
a. if your graphics card isn't too old and can decode the content you rencode setting 'Vapoursynth->Misc->Source->Libav hardware decoding mode' to a value > 0 (read sticky) might speed-up general processing
b. I would recommend to change the location of the temp folder, so one can easier have an eye on it.

--
Looking at the debug output:
- audio encoding call looks normal.
- Vapoursynth script seem okay
- video encoding looks okay (while I would never use 'ultrafast' )
- muxing call looks fine
-> don't see any reason why the output shouldn't play properly with a normal player. From the looks of it everything is properly flagged.
Vapoursynth doesn't remove or add frames and uses 'AssmueFPS' to make sure the output is reported as 24fps.
video encoding uses: --fps 24/1
muxing used: video:fps=24

Since you didn't include the analysis of the source in the debug output I assume the input also has 24fps so that should be correct.
-> have you tried another player like MPC-HC or VLC to be sure this isn't an issue with the player you are using?

Cu Selur