Then I did not explained my idea very well. The idea is to use the original video file as Direct Stream in both situations (with or without subtitle). But if you want forced subtitles it will transcode only position 01:23 - 01:25 where the forced subtitles are displayed (in a parallel running process). If the movie has a length of two hours and around 10 text lines of forced subtitles you won’t transcode for 99% of the time.
I know how to solve it today. My clients run perfectly with SRT subtitles. But some people do not want to use/buy specific client hardware and of course the feature request would supersede exporting subtitles, too.