HandBrake

I have a few videos which I previously encoded. Each took at least an hour, some even up to two hours. Back then I didn’t have their subtitle files, however now I do.

Is it possible to ‘add on’ subtitles to the output files without having to go through the whole encoding process again? I have tried using the output file, the same preset I used as before but this time I added the subtitle rack. It seems like it went through the entire encoding process.

As a related question, is there a way to change the font settings when burn-in is selected for the subtitles? I have searched the preferences menu for it but cannot seem to find anything. I also can’t find anything about it in the documentation online.

Possible, yes. If your files are MKV format, likely, using tools like mkvmerge.

If your files are MP4 format, less likely, because of limitations on the container.

Either way, handbrake would re-encode the source, because handbrake is a video encoder.

Oh, and if the subtitles are SRT format, handbrake does not do changes to fonts and such. It works well with Substation Alpha (SSA or ASS) font specifications, though.

To add just a bit, adding SRT files in a compliant container format does not necessarily require encoding. But not in Handbrake.
Burned-in subtitles always need re-encoding.