The following command keeps high quality on .mp3 (320 kbps), and metadata from .flac file are converted to ID3v2 format, which can be included in .mp3 files:
ffmpeg -i input.flac -ab 320k -map_metadata 0 -id3v2_version 3 output.mp3
The following command keeps high quality on .mp3 (320 kbps), and metadata from .flac file are converted to ID3v2 format, which can be included in .mp3 files:
ffmpeg -i input.flac -ab 320k -map_metadata 0 -id3v2_version 3 output.mp3