Request for advice #accessibility

I am looking for a tablet based solution that ideally satisfies the following constraints for a hard of hearing person:

1. high quality speech transcription
2. works for *groups of speakers*
3. ideally different speakers are colour coded
4. simple to use & easy to read full screen display
5. also works offline

I can satisfy some of these with tools I know of, but not all -most readily droppable features are 5 and 3.

any suggestions?