Version 5.4: streams no longer cause ffmpeg to hang. Current behavior:
1. If you start with playing a stream, no image is displayed or saved, continuing that way when switching streams (expected behavior).
2. If you then play a song, image is displayed/saved (expected) with that song title.
3. Once you switch back to a stream, no image is displayed, but an image identical to the song previously played is generated "behind the scenes" and saved with the stream's current title. Continuing to a different stream produces no additional saved images, until you play a song, and switch back to a stream, in which case the behavior repeats.
To sum up, once the spectrogram is "activated" by playing a song, when you switch to streams a non-displayed image will be generated once for the first stream that is a copy of the previously-played song's image, and named/saved with the stream title.
Of course, all images get deleted on MB restart when that option is selected. Question: is it possible to delete them instead on MusicBee's EXIT? Also, can the "images have been deleted" message be suppressed?
So, the hanging ffmpeg problem is solved (thanks!). The anomaly described above can be lived with IMO, but does generate unneeded additional images. Thanks again for your work.