Hello I'd like to use ffmpeg to change the audio speed in order to mux two bluray (having different fps), minimizing the quality loss (maybe lossless). I' like to use foss software only (I like ffmpeg).

1) could you suggest me some guide to learn how to encode audio without losses?
2) if I start from a lossless codec like DDP, TrueHD or DTS MA, should I convert them to a lossless codec? Which one? What about sampling, bit depth etc..?
3) if I start from a lossy codec like AC3, or DTS Core, should I convert them to a lossy codec? Which one? What about sampling, bit depth etc..?

Any additional resource is appreciated.