Adding extended subtitles past video length

I have multiple versions of a short film I’m ripping onto Plex, and want to combine the audio commentary track from the SD version, the trivia subtitle track from another SD release, and the HD video from the third.

Adding the commentary track was easy enough, and adding a delay of a couple seconds to sync it up went just fine. The problem is the trivia subtitle track, as it was a bonus feature on the DVD with several extra seconds on either side of the video. The subs start on a black screen about 5 seconds before the video proper starts, and continue about 45 seconds after it ends, again on a black screen.

Since the HD remaster does not have those extra seconds, it seems my only option is to use the “stretch” feature on the subs, making them go out of sync with the video. If I try to delay both the audio and video to sync it with the subs, VLC and Plex both just skip right to the start of the video, cutting off the first few seconds of subs, and end the playback at the end of the video, cutting off the remaining 45 seconds of subs. Is there any way to preserve the timing of the subs by adding a few seconds of black to either side of the video so the subs can play in their entirety?

Welcome!

Unfortunately MKVToolNix cannot help you with that. Players stopping playback when the video ends is common; you really would have to add more video content afterwards. MKVToolNix is not a full-blown video editor, though. It cannot generate video content, not even totally black screens.

Understood. Thanks for the reply!