[christopher5106]

What does this PR do?

The ref2va setup steps of MiniMax-H3 (MiniMaxH3Ref2VASetupStep) and Pika H3 Flex (PikaH3FlexRef2VASetupStep) resample a reference soundtrack onto the audio VAE's sample rate with torchaudio.transforms.Resample. torchaudio is not a diffusers dependency, so a reference soundtrack at any other rate than the VAE's 32 kHz (the 44.1 / 48 kHz audio track of most videos) fails:

ImportError: Resampling a MiniMax-H3 reference soundtrack from 48000 Hz to 32000 Hz needs `torchaudio`. Pass a waveform already at the audio VAE's sample rate to do without it.

Installing torchaudio doesn't help everywhere: it has no release for recent torch versions (the last on PyPI is 2.11.1).

This PR adds diffusers.utils.torch_utils.resample_audio, a plain-PyTorch port of torchaudio's default band-limited resampler (Hann-windowed sinc, lowpass_filter_width=6, rolloff=0.99), and uses it in both steps. Its output matches torchaudio.transforms.Resample to float32 rounding: identical at 48 → 32 kHz, within 4e-5 at 44.1 kHz. torchaudio's own transforms.Resample and functional.resample differ from each other by about as much.

echo still imports torchaudio, because it also needs MelSpectrogram, so this PR doesn't change it.

Tests

• tests/others/test_utils.py::TestResampleAudio: parity with torchaudio.transforms.Resample for 48→32, 44.1→32, 16→48 and 22.05→44.1 kHz (skipped without torchaudio), a 1 kHz tone keeping its frequency through 48 → 32 kHz, and checks on shape, dtype, the same-rate identity and the integer-input error.
• tests/modular_pipelines/minimax_h3: _normalize_audio_condition resamples a 48 kHz mono reference with torchaudio blocked in sys.modules.

The full minimax_h3 and pika_h3_flex suites pass on CPU, except 4 Pika H3 Flex ref2va tests (test_inference_is_not_nan, test_save_from_pretrained, and the two auto_cpu_offload ones), which fail the same way on main without this change.

Before submitting

• Did you read the contributor guideline?
• Did you write any new necessary tests?

[github-actions]

Hi @christopher5106, thanks for the PR! It does not appear to link an issue it fixes.

• If this PR addresses an existing issue, please add a closing keyword (e.g. Fixes #1234) to the PR description so the issue is linked.
• If you are the author of the model/pipeline this PR relates to, or part of the team we work with on it, tick the Are you the author (or part of the team we work with) of the model/pipeline this PR relates to? box in the PR description (if you removed the template, paste that line back, checked). This reminder then no longer applies.
• Otherwise there is nothing you need to do: a maintainer will look at the PR and add the no-issue-needed label to silence this reminder if it should stay open without an issue.

See the contribution guide for more details.

Please note that PRs without a linked issue are likely to be automatically closed 10 days after this notice.

Once the PR links an existing issue, the author box is ticked, or the no-issue-needed label is added, you can ignore this message — it stays here as a comment, but it no longer applies.