Merging mp4 files and preserving subtitles I'm in the process of digitizing my entire movie collection. For the most part, it's pretty smooth. I'm using Handbrake to put everything in mp4 format, and it's getting moved to my Plex server.
The only issue I've run into so far is when movies span multiple discs. I figure, once I'm digitizing, I should merge the two so I get a seamless viewing. The problem is, the only way I have to cleanly merge the files is a video editor (I happen to be using VSDC Free Video Editor, but I'm not married to it). The problem is that I lose subtitles. I've only had to do this once and I accepted the loss, but I'm going to hit it again later (think LoTR extended versions) and I don't want to lose them there.
Is there a way (preferably free, of course, but I'm open to all suggestions) to merge them without losing the subtitles? Or perhaps even a good way to add them back in after the fact?
Thanks!
You may consider to use either

Subtitle stream of mp4, e.g. https://gist.github.com/xer-rex/913db0dcef06c0304acd1fcb3712cd04
or
Burn-in subtitle in video of mp4, e.g. https://gist.github.com/xer-rex/bc80b5fbd23d1b91bb4737439816d773