Reusage of cached transcoded video stream

Hello, I have installed Serviio as a service on Synology DS413j. Unfortunatelly, DS413j is not powerfull enough to transcode streams in a real-time. However, I have noticed that the transcoded files are stored in /volume1/@tmp directory as files with .stf extension). After some time the file is ready and I can view the selected stream on my TV without any lag. Unfortunatelly, these files disaapear (probable after restart, or after specific timeout). Then I cannot view the original file and have to wait again for the result of transcoding.

I have question if it is possible to persist .stf files and use them to view the selected movies several times for a specific period of time (e.g. 1 month) without transcoding?
Is there any configuration available? How these files matches with original files?

Any tip is more than welcome.

[zip]

this file will be removed when you restart Serviio and/or when you play other file that needs transcoding. There is no way to keep them longer.