Link to issue number:

Fixes #19667
Fixes #19819
Reverts #19672

Summary of the issue:

Experimental code was recently added to NVDA (after 2026.1) that caused the 32 bit synthDriver shim to send its audio back to NvDA for playing, rather than playing it directly in its own process. This was done to test / prepare for the time when add-ons would be running in an app container, and therefore probably would not have direct access to the audio device.
However, currently this code is still quite unstable, causing NVDA to freeze when rapidly changing the speech rate, or arrowing up and down in lists, when using sapi4 or 32 bit sapi5.
This instability is most likely a similar issue to what was fixed in pr #19609, where RPYC is handoing the return of a call on the wrong thread. But in this case, it is calls to/from nvwave in NVDA's process.

Description of user facing changes:

Description of developer facing changes:

Description of development approach:

• Simply instruct the synthDriver process not to install the nvwave proxy that brokers back to NvDA.
• Reverts Re-enable audio ducking for proxied x86 speech synths #19672 so that 32 bit synthDrivers suspend audioDucking while they are running, as audioDucking cnanot be supported without brokering audio.

Testing strategy:

• verified freeze can no longer be reproduced in issues NVDA crashes when rapidly scrolling through lists and rapidly pressing keys using the Microsoft Text to speech engine #19667 and synthDriverHost freezes when rapidly adjusting voice/rate with SAPI4 #19819.
• Make a local signed copy, install and test that audio ducking is disabled when using sapi4, and reenabled when swtching back to espeak.

Known issues with pull request:

Code Review Checklist:

• Documentation:
  • Change log entry
  • User Documentation
  • Developer / Technical Documentation
  • Context sensitive help for GUI changes
• Testing:
  • Unit tests
  • System (end to end) tests
  • Manual testing
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers
  • Localization in other languages / culture than English
• API is compatible with existing add-ons.
• Security precautions taken.