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

[Selur]

okay, no clue why that helps.

Try also keeping 'Create qp file chapters' enabled while making sure that 'x264->Frames->Advanced Frame Settings->Open GOP' is disabled.

So what's "Create qp file chapters" is use for?

It makes sure that at each chapter point an I frame is created to make sure that jumping to the chapter point properly works.

Cu Selur

Ps.: Using ffmpeg instead of MP4Box for muxing also works.