Decoder was not found for this format?

[Biff]

This message appears when I try to play .m4a files:

File: I:\j\John Williams - Indiana Jones and the Dial of Destiny (2023)\02 - Helena's Theme.m4a
Code: -1 (FFFFFFFF)
Message: Decoder was not found for this format.

What could I do to play them?

[Алексей Долматов]

Need a sample file. If mediainfo determines it, then you can add information from it.

To check: make sure that plugins are active and the option to use system decoders is enabled.
Also, be sure to indicate the exact version of the player and the exact version of the system.

[sveakul]

This message appears when I try to play .m4a files:

File: I:\j\John Williams - Indiana Jones and the Dial of Destiny (2023)\02 - Helena's Theme.m4a
Code: -1 (FFFFFFFF)
Message: Decoder was not found for this format.

What could I do to play them?

Do you get the message for ALL .m4a files?  Be sure that Prefs/Plugins/Decoders/Advanced Audio Coding v2.4.6.1 is present and active/checked.

If not present, check that the folder bass_aac exists with bass_aac.dll in your plugins directory.  If they don't, add them (can be extracted with 7-Zip from the file
https://www.aimp.ru/?do=download.file&id=31 or your backup directory).

If it is, try un-checking Sound Output/Transform/Allow System Decoder Usage.