When a Tika server is configured, audio cover art is extracted through it by
default, selecting the tagged front cover (ID3 APIC 'Cover (front)') via
/unpack/all sidecar metadata, else the first embedded image. TikaDecoder picks
by mime type: audio/* front cover, everything else the largest preview.
THUMBNAILS_PREPROCESSOR_AUDIO_PROCESSOR=builtin forces the in-process extractor;
it is deprecated and slated for removal in the next major.
Dominik Schmidt
1592ab25f2