How to prevent subtitle format change?

[voska7]

how to prevent subtitle format change? this is the source subtitle formate

Text #1
ID                                       : 3
Format                                   : UTF-8
Codec ID                                 : S_TEXT/UTF8
Codec ID/Info                            : UTF-8 Plain Text
Duration                                 : 1 h 3 min

after convert output file subtitle contains like this

Text #1
ID                                       : 3
Format                                   : ASS
Codec ID                                 : S_TEXT/ASS
Codec ID/Info                            : Advanced Sub Station Alpha
Duration                                 : 1 h 3 min
Compression mode                         : Lossless

[RandomEngy]

The HandBrake engine controls the output subtitle format. I don't think there's a way to configure what format it ends up in.