The following command will convert WEBM to FLAC at 16 bit and 48000 hertz.
ffmpeg -i in.webm -af aresample=resampler=soxr:out_sample_fmt=s16:out_sample_rate=48000 out.flac
The following command will extract audio from WEBM and copy it to OGG container without transcoding.
ffmpeg -i in.webm -vn -c:a copy out.ogg