New Text to Speech experiment

[dkotter]

Note

This is dependent on changes coming to the OpenAI Provider (see PR 42) or Google Provider (see PR 31)

What?

Adds a new experiment, Text to Speech, that allows editors the ability to on-demand generate speech for a post, including the title and post content. This is then displayed as a player on the front-end or that can be turned off on a post by post basis.

Why?

Adding support for Text to Speech allows sites to provide their users with the ability to listen to content instead of having to read the content.

How?

• Registers two new Abilities, ai/speech-generation and ai/speech-import. These can be used to generate speech from text and import that speech as an audio file into the Media Library
• Add shared functionality across multiple classes that can take in some text content, chunk that content down (if needed, to stay under API limits. Note only works if the format is MP3) and send that content off to generate speech for. It then combines all the returned speech data into a single audio file which we import into the Media Library. This functionality is used both if someone directly uses the Abilities above and when audio generation is manually triggered in the admin
• Add a REST endpoint that is used to track audio progress, allowing audio generation to happen via cron events. This allows longer running processes and processing of audio even if someone navigates away

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Opus 4.8
Used for: Help with initial planning and implementation. Refinement, review and testing done by me

Testing Instructions

1. Requires an AI Provider that supports Text to Speech. Easiest way to test for now is to download the OpenAI Provider plugin from this PR or Google Provider plugin from this PR
2. Turn on the Text to Speech experiment
3. Go to a post and find the Text to Speech sidebar panel. Click on the Generate Audio button
4. Audio generation will take a bit but is run in the background via cron jobs. Easiest is to just stay on the page until it is done but you can navigate away and come back later
5. Once finished, you should see an audio player render in that panel, along with a toggle to display the audio player on the front-end and a button to regenerate audio
6. View the front-end and ensure the audio player shows there

Screenshots

Changelog Entry

Added - New experiment, Text to Speech, that allows you to generate audio for a specific post and then render audio controls on the frontend.

[github-actions]

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Co-authored-by: dkotter <dkotter@git.wordpress.org>

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[codecov]

Codecov Report

❌ Patch coverage is 75.88571% with 211 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.43%. Comparing base (f0764fb) to head (b80097e).

Files with missing lines	Patch %	Lines
...udes/Experiments/Text_To_Speech/Text_To_Speech.php	63.15%	49 Missing ⚠️
...es/Experiments/Text_To_Speech/Speech_Generator.php	21.15%	41 Missing ⚠️
includes/Abilities/Speech/Generate_Speech.php	78.03%	29 Missing ⚠️
includes/Abilities/Speech/Import_Base64_Audio.php	83.92%	27 Missing ⚠️
...ncludes/Experiments/Text_To_Speech/Job_Manager.php	85.71%	25 Missing ⚠️
...des/Experiments/Text_To_Speech/REST_Controller.php	85.57%	15 Missing ⚠️
includes/helpers.php	71.42%	10 Missing ⚠️
...udes/Experiments/Text_To_Speech/Audio_Combiner.php	77.14%	8 Missing ⚠️
...des/Experiments/Text_To_Speech/Content_Chunker.php	89.18%	4 Missing ⚠️
includes/REST/Models_Controller.php	25.00%	3 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop     #888      +/-   ##
=============================================
- Coverage      79.74%   79.43%   -0.32%     
- Complexity      2469     2648     +179     
=============================================
  Files            104      112       +8     
  Lines           9992    10867     +875     
=============================================
+ Hits            7968     8632     +664     
- Misses          2024     2235     +211     

Flag	Coverage Δ
unit	79.43% <75.88%> (-0.32%)	⬇️

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