Audiobook renders were locked to the model's most deterministic preset (32
steps / 2.0 guidance / model-default temps) with no way to change it, which is
why books sounded flatter than the same voice on the Voice page. Open that up
without changing any default byte-for-byte.
- Production Overrides in the Audiobook tab: position_temperature,
class_temperature, num_step, guidance_scale, postprocess_output (+ seed),
reusing the Voice page's panel. Unset reproduces today exactly.
- IndexTTS2 graded emotion (emo_vector / emo_text / emo_alpha) reaches the
longform path via a typed engine-options object; engines that don't
understand an option ignore it (no crash across the ~14 backends).
- Cache opt-out ("vary repeated lines") so identical lines can get distinct
takes; default off keeps the content-addressed replay.
- Markup reference now lists the reaction tags that already work in audiobooks;
docs/expressive-speech.md corrected so no recipe it names is unreachable.
- Fix AudiobookGenerateBody dropping `language`, so audiobook language
selection actually reaches the backend.
Every new param is folded into BOTH cache layers (chapter + segment) and the
per-chapter preview, so changing a knob re-renders instead of replaying stale
audio — and an all-default request keeps its old cache key, so existing books
don't re-render. Regression tests: tests/test_audiobook_expressive.py (backward
compat, cache-signature loop, preview/render parity, engine-ignores-unknown,
cache opt-out, emotion reaches engine) + audiobookOverrides.test.jsx.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
