Comment-only pass over the Python this PR touches: drop what the code already
says, collapse multi-line explanations that still read on one line, and keep
the reasoning that is not recoverable from the code. No code, docstring
semantics or behaviour changes; verified with an AST comparison against the
previous revision, and the backend suite is unchanged (same 37 environment
failures as before: the API integration tests that need a live keyed server,
the flash-attn install hooks, and the GPU memory fields).
A candidate clip that decodes to fewer frames than the reference was
compared only over the shared prefix, so good early frames could PASS a
truncated or corrupt render. Record both frame counts and gate a mismatch
as FAIL, matching the harness contract that the requested shape is held
fixed. Extend the selftest with a truncated-clip case.
An empty or corrupt clip decode crashed clip_metrics on frame indexing; it now
returns a zero-frame FAIL record. A NaN candidate audio RMS compared False
against every threshold and slipped past the silence trip-wire; NaN now counts
as a collapse.
HunyuanVideo-1.5 (the 8.3B DiT with Qwen2.5-VL + ByT5 text encoders) loads
through the hunyuanvideo-community Diffusers repacks; tencent's own repo is
the original non-diffusers layout and cannot load as a pipeline, so only the
community 480p/720p t2v repos are trusted. Two pipeline quirks, both verified
against pipeline_hunyuan_video1_5.py in diffusers 0.39, shape the wiring:
- __call__ takes no guidance kwarg: CFG lives on the pipeline's guider
component (ClassifierFreeGuidance, shipped at scale 6.0). The family gains
guidance_via_guider and generate() writes the requested scale onto
pipe.guider instead of passing cfg_kwarg, which the pipeline would reject.
- __call__ has no callback_on_step_end: progress and cancellation fall back
to a scheduler.step wrapper (one call per denoise step), installed for the
duration of the call and always restored. Cancellation unwinds the loop by
raising through the wrapper and surfaces the same cancelled sentinel the
callback path uses.
The VAE compresses 16x spatial / 4x temporal, so sizes snap to /16 and frame
counts to 4k+1. The transformer declares _repeated_blocks and CacheMixin, so
the regional compile profile and the step cache both apply unchanged.
scripts/video_quality.py is the video accuracy gate, the analogue of
scripts/diffusion_quality.py with the same pure-numpy PSNR/SSIM math so image
and video budgets compare: fixed prompt/seed/shape, one short clip per
candidate against a reference clip, per-frame SSIM/PSNR over sampled frames,
a temporal-consistency deviation (motion-energy series error, catching
flicker SSIM alone misses), black-frame/NaN collapse checks, an audio RMS
silence trip-wire for LTX-2, and wall time + peak VRAM per candidate.
Verdicts map the standing budget: ssim >= 0.75 passes, >= 0.50 warns,
anything lower or any collapse fails. --selftest runs the metric path on
synthetic clips with no GPU or model.
