Sonos doesn’t support variable bitrate WMA files.

The bitrate needs to be 320kbps or less and the sample rate no higher than 48kHz.

https://support.sonos.com/en-us/article/supported-audio-formats-for-sonos-music-library

We don’t think that’s correct, apologies. Most of our files are variable bit rate, and they are recognised, indexed and played just fine by Sonos.

In fact, one of our most recently obtained WMA files that isn’t indexed has a constant bit rate of 64kbps, so it doesn’t seem to matter if the bit rate is constant or variable. We think it’s something else, maybe a particular tag or property that Sonos expects, aside from the usual metadata?

Thanks for that. Sorry, we forgot to mention that we checked that, too - all our WMA files, regardless of being recognised and indexed or not, are less than 320kbps. 

Look for characters Sonos does not support in your track names.

I found a simple rename to x1, x2 got a couple missing files to appear. Renaming them back to the original names minus the unsupported characters worked.

Thanks for the suggestion. Our WMA files only use letters, digits and underscores in their names. We tried renaming one of the missing files to "x1" and updating the music library, but Sonos still didn't discover it. We think it must be something inside the missing WMA files that Sonos doesn't like or support. 

Hi @The Krollmanns 

Welcome to the Sonos Community!

Do the problem files show up if you go to Browse » Music Library » Folders » epath to shared folder] » lpath to file(s)]? If so, then the issue is likely metadata related.

Otherwise, I recommend you get in touch with our technical support team who will be able to look more closely via a remote session to your computer.

I hope this helps.

Hi Corry

Thanks for your response. Unfortunately the files do not show up at all when trying to locate them as described above. It’s as if they didn’t exist in the music library. Even the album folder and album art are missing if all WMA files of an album are not recognised (instead of showing an empty folder).

We will contact technical support as advised.

Could you have files and folders in the path with differing permissions to the rest and the account Sonos is using has no access to those areas?

Good thought, however, our files are stored on a USB medium that does not have file-level permissions, and other applications (file explorers, media players) can access and play the missing WMA files just fine.

We’ve opened a case with Sonos technical support today, and it has now been escalated to level 2 for further investigation. 

we are having a similar problem - has the problem described in this thread been resolved yet?

Sonos Support investigated and responded that the WMA track was not being added because its bit depth was 32-bit.
They explained that the Sonos Music Library can handle audio files with bit depths of 16-bit or even 24-bit but only for FLAC and ALAC files as provided in their knowledge base article "Supported audio formats for Sonos music library". 
It is possible to get the track added to the Sonos Music Library after converting or downgrading the bit depth from 32-bit to 16-bit. You’ll need a third-party app or service to convert or downgrade the file to 16-bit audio.