Conversion settings

Settings > Conversions sets the defaults for Conversions. Any job can override them.

General

Setting	Default	Effect
Enable Conversions	on	Off, creating, bulk queuing or retrying a conversion is refused with HTTP 409, a job already queued fails with a message saying so, and Auto-Reformat on Import queues nothing
Conversion Folder	empty	Scratch space. Empty uses the system temp folder
Concurrent Conversions	2	1 to 4. Keep this times Threads Per Job at or below your core count. The page warns when it’s higher
Threads Per Job	Auto	FFmpeg threads for each job, in Advanced view. Auto leaves two cores for ABM and splits the rest across the jobs running at once, so 8 cores and 2 concurrent jobs gives 3 threads each. Or pick a fixed count
Process Priority	Normal	Low keeps the rest of the system responsive. High finishes sooner

Audio quality defaults

Setting	Default
Default Output Format	M4B (also MP3, M4A, FLAC, Opus)
Default Bitrate	128 kbps (64, 96, 128, 192, 256, or Copy for no re-encode)
Default Sample Rate	Auto, which passes no rate and leaves it to FFmpeg. Or 22050, 44100 or 48000 Hz, which resamples. Opus only takes certain rates, so 22050 becomes 24000 and 44100 becomes 48000 (the log says so)
Default Channels	Auto, which keeps the source layout. Mono mixes down to one channel for smaller files. Stereo forces two

The two rate and channel lists only accept what the page offers. A bad saved value loads as Auto.

Codec options

Format	Encoder	Options
M4B, M4A	AAC	AAC Profile (AAC-LC by default) and AAC VBR, quality 1 to 5. Bitrate applies when VBR is off. AAC-LC is the only profile, because the encoder can’t make HE-AAC. A saved HE profile loads as AAC-LC
MP3	LAME	VBR quality 0 to 9 (4 by default) and Joint Stereo (on). Bitrate applies when VBR is off
Opus	libopus	Variable bitrate (on) and Application: Audio (default), VoIP or Low Delay
FLAC	FLAC	Compression level 0 to 12 (5 by default). Bitrate is ignored

A bitrate of Copy skips re-encoding and every codec option.

Chapter handling

Setting	Default	Effect
Default Chapter Behavior	Auto	Preserve if they exist, generate if not. Others: preserve only, always generate, none
Chapter Naming Format	Chapter {n}	Names the chapters ABM has to make up. {n} is the number and {title} the source file’s name. Chapter titles from the files or from Libex are kept
Silence Detection	off	For a file with no chapters, ABM makes chapters at the longest pauses in the audio. It is used by Split Chapters and by Ensure Chapters on a single file when Libex has no chapters. Off, a split of such a file fails
Target Chapter Length	600 s	Shown when Silence Detection is on, 60 s or more. Each chapter ends at the longest pause within half this length either side of it, or at this length if there is no pause. A short tail joins the last chapter, and the chapters cover the whole file
Chapter Image Handling	Keep in file	Or remove, or extract to a folder

Metadata handling

Setting	Default
Preserve Metadata	All metadata
Embed Cover Art	on (JPEG only, for Audiobookshelf)
Cover Art Max Size	1000x1000

File management

Setting	Default	Effect
Enable Recycle Bin	on	Originals go to the bin instead of being deleted
Recycle Bin Path	empty	Empty uses /config/recycle/conversions
Retention Period	7 days	Items older than this are deleted by the recycle cleanup task. 0 keeps them for good
Auto-Empty When Bin Is Large	off	Turns on the threshold below
Auto-Empty Threshold	10 GB	After a conversion, if the bin holds more than this, the oldest items are deleted
Delete Original	off	Default for each job, overridable
Update Library Paths	on	Book records follow the converted files
Auto-Reformat on Import	off	Converts newly imported books that arrive in another format, using the defaults above
Backup Original Metadata	off	Before converting, writes a JSON file to a .metadata_backup folder inside the book’s folder. It lists each original file’s name, format and size, plus the tags and chapters embedded in it

Advanced FFmpeg

FFmpeg Path (empty finds it on PATH), Custom FFmpeg Arguments (appended to every command; bad ones make conversions fail), Logging Level (error by default) and Keep FFmpeg Logs (off).