BDSup2Sub is a tool I wrote initially to convert captions demuxed from a Blu-Ray transport stream (M2TS) into the DVD VobSub format (SUB/IDX) used by many DVD authoring tools - hence the name. It is a free and open source sup to sub converting application that's light on system resources, attractive, straightforward, reliable and advanced.
Here are some screenshots to illustrate the features and user interface of this application:
MixPad
ocenaudio
Audials Tunebite
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VideoPad Video Editor Free