I have now compiled a small audio test app and installed it on one of my iOS test devices (iPhone 6s, iOS 15.79) (Ad hoc).
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I used images as a spacer and specified the height/width in px or % values. This seems to work with Companion but not with compiled app (IPA). It only works when an empty (4px) png is assigned to the images. So that's not a problem if you know it.
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Images cannot be assigned to buttons with the IPA (these are not displayed with the IPA). Companion works. You have to use clickable images instead. If you know that, that's not a problem either.
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Material icons do not work with Companion or with the IPA, although they are displayed correctly in the designer (► / ■ play_arrow / stop).
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"invalid application. Irritants: (#!null)" after opening the IPA for the first time. Nevertheless, the app works just as well as with Companion). The problem does not occur with Companion.
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As soon as the app goes into the background, the sound stops completely (music & voice). After the app is back in the foreground the sound continues to play. Companion & IPA. (Of course PlayOnlyInForeground is not enabled.)
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MP3, M4A, AAC,... audio files cannot be looped gapelessly (as I discovered in my last test almost 2 years ago - at least with Companion). So it remains that only uncompressed audio formats such as WAV, AIFF, ... or so-called IMA4 files (compressed to about a quarter) work. I noticed the same thing almost 9 years ago when I took my first steps with Xcode and Swift 1.0. And that doesn't seem to have changed to this day .
If desired, I can forward the (test) aia & IPA to the MIT AI team. @ewpatton
PS: I will check it soon also on an iPad Pro (12.9, 4th gen - iOS 16.7 and 17.0.2).