How to merge DASH segmented STPP subtitles from an encrypted stream?

[user1020]

Hi all,

I used N_m3u8DL-RE (with no options) to download an encrypted DASH livestream. At the end of the stream, I used CTRL + C to stop the download so I was left with individual folders for video, audio, and subtitles plus their respective DASH segments. I was able to successfully merge and decrypt the segmented video and audio streams but I need help merging the segmented subtitle files.

I have these files for the subtitles:

_init.mp4
151619025242685.m4s
151619025600042.m4s
151619025960402.m4s
151619026320762.m4s
151619026681122.m4s
...and more

Can someone help me with steps to take for vtt/srt subtitles? Also, in the future, is it possible to have N_m3u8DL-RE automatically merge segments when I use CTRL + C to stop downloading a finished livestream?

Thanks in advance.


Update with solution:

Hope this helps someone with similar problem.

0) cd into segment directory
1) copy /B _init.mp4 +*.m4s subtitles.mp4
2) ffmpeg -i subtitles.mp4 -f data -map 0 -c copy subtitles.ttml

Timing will probably be messed up with large hour numbers. Something like 442421:06:32.002. You will need to manually edit hour to start at 0 and +1 every time hour increases.

Ex)
442421:06:32.002 --> 00:06:32.002
442422:18:49.150 --> 01:18:49.150
442423:58:11.169 --> 02:58:11.169
...and so on

3) Open subtitles in Notepad++/text editor and fix timing (use 'find and replace all').
4) Open subtitles in Subtitle Edit and synchronize with video (use 'adjust all times')
5) Save as desired format
https://github.com/yt-dlp/yt-dlp/issues/656#issuecomment-894869390