By default yes — 48 kHz MP3 → 48 kHz OGG, 96 kHz → 96 kHz. If you need to downsample for compatibility (96 kHz studio masters → 44.1 kHz for CD burning), the advanced sample-rate option uses a high-quality resampler (libsoxr or sox-equivalent) with no audible aliasing.
Same-codec re-mux (e.g. FLAC stream inside one container moved to another): 10-30 seconds. Re-encode to a different codec: typically 10-20% of source duration, so a 1-hour MP3 → OGG finishes in 6-12 minutes.