* fix(audiobook): chapter render no longer crashes on mixed 1-D/2-D audio chunks (#897)
Root cause: synthesize_chapter (backend/services/audiobook.py) built
inter-span pause silence as bare 1-D torch.zeros(n) while every real
engine's synth returns (1, samples) per the TTSBackend.generate contract
(OmniVoice's model.generate(...)[0] included) — so the chapter's final
hard concat in chunked_tts.concatenate_audio_chunks hit
torch.cat with mixed ranks and died with
'RuntimeError: Tensors must have same number of dimensions: got 1 and 2'.
Any chapter containing a [pause] span (Stories/audiobook longform)
crashed; existing tests missed it because their stub synth returned 1-D.
The crossfade branch had the same latent bug for mixed-rank chunks.
Fix, both layers:
- concatenate_audio_chunks now normalizes chunk shapes before any cat
(_normalize_chunk_shapes): lower-rank chunks gain leading singleton
dims to the highest rank present, then singleton channel dims
broadcast to the widest channel count (mono follows stereo). Covers
both the hard-cut and crossfade branches; homogeneous input passes
through untouched, so all-1-D / all-2-D callers keep their exact
output shapes. No future backend's output rank can re-break the join.
- synthesize_chapter materializes silence AFTER the loop, matching the
rendered audio's channel dims / dtype / device — the same pattern
generation.py's _render_with_pauses already uses for the single-shot
path — so the data is rank-consistent at the source too. A
silence-only chapter stays 1-D float32 as before.
Regression tests: mixed-rank hard-cut (both orders), mixed-rank
crossfade, mono->stereo broadcast, all-1-D/all-2-D shape stability, a
2-D-engine + [pause] chapter through synthesize_chapter (the exact #897
scenario), and a spy asserting the parts reaching the concat are
rank-homogeneous. All fail before the fix with the reported error.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
* docs(changelog): add the audiobook pause-span concat fix under [Unreleased] (#953)
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---------
Co-authored-by: mergetest <test@local>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
