iOS 13 sound starts once you reset all

[KatieWoe]

Found when looking at phetsims/phet-core#64. Found on John Travoltage but not on Area Builder, so I think it is likely a Tambo issue. Not found on iOS 12.
When you start up the John Travoltage sim, no sound plays. Moving pieces doesn't cause a sound, and neither does muting and unmuting. However, if you hit the orange reset all button, that sound will play, and so will normal sounds after that.

[jbphet]

One of the roots of this problem is that the user agent has changed in iOS 13, and the code in platform.js no longer recognizes that it's running on Mobile Safari (see phetsims/phet-core#64). I have done some experiments and found that with the current autoplay behaviors implemented in Chrome, Firefox, Edge, Safari, and Mobile Safari, the code that detects and resumes a suspended audio context can be generalized to work in all cases so that detection of Mobile Safari is no longer necessary. However, this will require a QA cycle and a maintenance release.

[jbphet]

The code for resuming the audio context has been rewritten so that it is no longer necessary to have any platform-specific portions. This fixes the issue with sound not playing initially on iOS 13. This will require a maintenance release for all sims that use sound.

[jbphet]

This should be fixed on master. I'm going to assign it back to QA to verify that the fix works and to regression test the behavior on our other supported platforms. Assuming it all checks out, this should then be assigned to @jonathanolson to deploy in a maintenance release.

[KatieWoe]

• Win 10 chrome
• Win 10 firefox
• Win 10 edge

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• Win 7 chrome
• Win 7 firefox
• Win 7 internet explorer

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• Mac 10.14 chrome
• Mac 10.14 safari

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• Mac 10.13 chrome
• Mac 10.13 safari

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• Mac 10.12 chrome
• Mac 10.12 safari

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• Mac 10.11 chrome
• Mac 10.11 safari

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• Mac 10.10 safari

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• Chrome OS

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• iOS 13
• iOS 12
• iOS 11

[jbphet]

@KatieWoe - I believe the issues that was causing the alert message is now fixed, please resume testing.

[KatieWoe]

Done. Things look ok. Everything tested with touch when possible. Win 7 IE skipped since it doesn't support the sound in question.

[jbphet]

I tested this issue on my iPhone 8 running version 13.1.2, and the sound issues didn't occur. I was wondering if maybe Apple fixed it, so @KatieWoe and I just tested on PhET's 6th generation iPad (which hasn't been assigned a name yet) running 13.1.2, and the problem does still occur there. Here was the test sequence:

• Load the currently live version of John Travoltage (v1.5.11)
• Drag the leg back and forth before doing anything else (no sound is produced)
• Keep doing this until a discharge occurs (still no sound is produced)
• Press the reset button - we heard the reset sound, followed by the discharge sound and the verbal exclamation at this point

Depending, I think, on what version tambo a sim has, some of them recover after a reset, some don't. This was based on testing the live versions of Friction (v1.5.9), Resistance in a Wire (v1.6.8), and Ohm's Law (v1.4.6).

[jbphet]

@jonathanolson and I are working through a maintenance release to address this. It is turning out to require a number of unique patches, so we are thinking that would should only patch the sims that need it. Sims that don't need it either have no sound functionality at all or don't manifest the problem where sound doesn't work. The acid test for whether sound functions is to load the sim, drag (but don't tap) your finger on the screen without selecting a screen or doing anything else on the sim, then go do something in the sim that should produce sound. The currently live version of the "Build a Fraction" sim (v1.0.9) exhibits this problem. The current version of "Balancing Chemical Equations" (v1.2.8) does not.

It would be possible, albeit time consuming, to figure out exactly why the sound gets locked up in some sims and not others. I don't think that this is worth the time and effort. The likely explanation is that there is a previous version of the tambo code that tries to resume the audio context on a touchdrag event and disconnects the listener, but doesn't check whether the operation worked, and it doesn't. In other words, it's disconnecting itself before the job is done. We should just go ahead and patch such instances of the tambo code.

[jbphet]

For future reference, here are the published sims for which tambo was not patched, either because they don't use sound or because they didn't manifest the audio problems on iOS 13:

• balancing-chemical-equations 1.2 phet
• blackbody-spectrum 1.0 phet
• fraction-matcher 1.2 phet
• fractions-equality** 1.1 phet
• molarity 1.4 phet,phet-io
• ph-scale 1.3 phet
• ph-scale-basics 1.3 phet
• reactants-products-and-leftovers 1.2 phet
• rutherford-scattering 1.1 phet
• states-of-matter 1.1 phet
• states-of-matter-basics 1.1 phet

[jbphet]

A fix has been implemented and deployed as part of a maintenance release. Closing.