This thread may be helpful: 

What size is the artwork? Generally speaking apps dump their file cache on suspend, so they need to reload those files on resume. If you have large artwork, or your NAS is lame and can’t handle streaming at the same time as multiple large downloads, then it might be a problem.

Why do you need to see 28 album covers at the same time while playing anyway?

With music services, they have the advantage that they can provide art at different resolutions to different parts of the app, so they can give up thumbnails for album list view and nice big art for Now Playing. NAS playback uses a single resolution everywhere so you have to trade off slow downloads vs pretty art if you have a NAS that can’t handle the load.

Thanks GuitarSuperstar, I didn’t find that topic on my initial search. Conclusion: I am not alone!

Thanks controlav.

> What size is the artwork?

Mostly 512x512px, 30-80KB

> Generally speaking apps dump their file cache on suspend, so they need to reload those files on resume.

If it’s a cache dumping issue, it is not clear when this is happening. When I switch back to the app the artwork is still displayed, for about half a second before disappearing.

> If you have large artwork, or your NAS is lame and can’t handle streaming at the same time as multiple large downloads, then it might be a problem.

The NAS and WiFi seem fine for all other purposes. The artwork load is always very slow, even when there is no music streaming or any other activity on the NAS or WiFI. So prima facie I am blaming the SONOS app.

Note I am currently in test mode, before I load the other the other 500 albums onto the NAS, which I am now reluctant to do ...

> Why do you need to see 28 album covers at the same time while playing anyway?

That is not the use case. I am switching back till the app in order to select the next album to play. I can do this well before the artwork has finished loading, making the artwork pretty much useless for finding an album.

THEORY: could it be that the the app is retrieving all of every music file, every time time the app is foregrounded, just to extract the artwork from each? If so, it really needs to have a much longer-lasting artwork cache, stored locally with the app.

All the controller does for artwork is issue an http GET call to the coordinating speaker: the speaker actually grabs the art from the NAS and passes it back to the controller. I have no idea how this process could be as slow as you describe.

You could try SonoPad/SonosPhone to see if that is any better, but its unlikely as 98% of the codepath will be the same as the Sonos app.

A full network trace or NAS log is likely the only way to figure out where the delay is occurring.