handbrake passthrough to mkv?

[electronicsguy]

Hello,
could someone explain me what this means. I am reading this URL:

https://trac.handbrake.fr/milestone/HandBrake%200.9.9

"can be passed through to MKV (but not MP4)".

I don't understand what passing through a subtitle to mkv means. Which mkv are they referring to - the source mkv or a destination mkv? And what is the purpose of this pass through?

Thanks,

[Romansh]

It means transferring from the source (in the case of Blu-ray subtitles, can be a Blu-ray folder structure or an MKV file such as created by MakeMKV) to the output without modifying the stream.

Since you can't put Blu-ray subtitles in an MP4 container, you'll have to burn them in (render the subtitles over the video, rather than place them in their own track which you can turn on or off).