Local Media Information (From the OuterTune wiki)

The local song scanner can be accessed from the top of the home screen, or through Settings -> Library and content -> Local media. Here, you can configure how OuterTune will discover songs on your device. Local scanner settings Scan locations

If this is your first time using the app, you will need to configure which folders to scan for songs in. In the dialog, you can toggle between inclusion (whitelist) and exclusion (blacklist) mode. You can blacklist folders within a whitelist folder, but NOT vice versa. Scanning manually

Tap the scan button to scan for songs.

Additionally, you can configure the scanner checkboxes.

Rescan: There are two scan types, "quick scan" and "full rescan". By default, OuterTune utilizes "quick scan" which performs much faster than "full rescan", but the metadata of existing songs will not be updated when a "quick scan" runs. Enabling "full rescan" disables "quick scan" and will always reload metadata for all songs.

An additional checkbox is available to enable linking local songs of with artists on YouTube Music. Please note that the accuracy of this feature is dependent on YouTube search and your song's metadata tags. Not all artists may be available on YouTube Music and/or artists with similar names may not be correctly identified. This feature is experimental and we do not recommend you enable it unless you really need it. This feature may use significant resources and/or take a long time to process depending on your library size. If you wish to go back to non-linked artists, just run a "full rescan". Scan automatically

This toggle periodically runs a "quick scan" to search for songs. By default, the automatic scanner is disabled and will need to be manually enabled.

Please note, if linking local songs with artists on YouTube Music is enabled, this scanner will run the (potentially very slow and battery hungry) YouTube Music artist linking job automatically as well. Scanner sensitivity and strict file names

Configures what criteria the local scanner will use to differentiate between songs. Below are some common use cases:

Problem: Same song titles, different artists Ex. "Bad Habits" by Ed Sheeran and "Bad Habits" by Bring Me The Horizon & Ed Sheeran are registered as the same song:
    Solution: Change scanner sensitivity to "Match title and artists", the scan with the rescan checkbox enabled
Problem: Migrating from songs without metadata tags to songs with metadata tags:
    Solution: Scan with "Match title" on the new audio files, then again with "Match title and artists" to update the metadata yet still preserve stats like play counts, and playlists.
You have multiple versions of the same song in different folders, but they are being detected as the same song:
    Enable Strict file names

Playing uncommon/obscure audio codecs that the Android system does not support

Warning

Experimental, in development feature.

Some audio codecs may not be playable by the Android system (ex. ALAC). You may enable FFmpeg decoders to play these files Select the decoder under Settings --> Player and audio -> Advanced -> Audio decoder. Then force close the app and re-open it for changes to take effect.

Only the "full" build variant of the app has support for FFmpeg decoders for OuterTune versions 0.9.4 and higher. Please note this feature is a work in process and thus files not detectable by Android's MediaStore may not be playble at this moment. Eventually, once the feature is completed, you should be able to play files in .nomedia folders, and even files with obscure extensions.