Regardless of the source, Apple converts the audio stream to a 44.1Khz lossless stream in ALAC format. AirPlay Recorder allows you to save this stream. On the Mac and PC, the stream is saved as-is in ALAC format so you can then transcode/convert to another format without further compression loss. On Android, the stream is saved as a high bit rate (180-240Kbps) AAC file to ensure Android compatibility and also to save on storage space.
As long as the source provide correct metadata (start time, end time, artist/song/album name, artwork, etc.), AirPlay Recorder will embed this information into the saved files.