Using ffmpeg, can I burn in subtitles directly from an mkv subtitle track?

[raphael_is_red]

I have an mkv with multiple subtitle streams. I know I can use mkvextract to extract one of those subtitle streams to a file, for example, sub.srt. I can then burn those subtitles into the new video with ffmpeg like so:

ffmpeg -i video.mkv -vf subtitles=sub.srt out.mp4

I also know I can use -map to select video, audio, and subtitle tracks and encode those into the new video, again something like so:

ffmpeg -i video.mkv -map 0:0 -map 0:1 -map 0:4 -c:v copy -c:a copy -c:v copy out.mp4

However, what I can't figure out is how to transcode a video and burn in the subtitles into the new file (not just adding a subtitle track, but burning them into the video) not by reading it from a subtitle file but directly from the old video stream itself.
Any ideas?

[Baldrick]

See https://trac.ffmpeg.org/wiki/How%20to%20burn%20subtitles%20into%20the%20video .
The last step. Maybe it only works for picture based subs.