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perf: skip x264 scene-cut analysis on LTX-2.3 PyAV save path (env-configurable) #15

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Merged
Johan-de-R merged 1 commit into from
Jul 7, 2026
Merged

perf: skip x264 scene-cut analysis on LTX-2.3 PyAV save path (env-configurable) #15

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3 changes: 3 additions & 0 deletions examples/diffusers/Dockerfile.dreamverse
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Expand Up @@ -36,14 +36,17 @@ RUN . /opt/venv/bin/activate \
# the exact commit these patches were authored against, so they apply clean.
COPY patches/ltx23_gpu_worker_megacache.patch /tmp/megacache.patch
COPY patches/x264-threads-cap.patch /tmp/x264-threads-cap.patch
COPY patches/pyav-scenecut.patch /tmp/pyav-scenecut.patch
# NOTE: verify by grepping the patched source, NOT by importing fastvideo --
# importing pulls in triton, which fails to init its driver in a GPU-less build
# ("0 active drivers").
RUN SP=/opt/venv/lib/python3.12/site-packages \
&& patch -p1 -d "$SP" --forward --fuzz=0 < /tmp/megacache.patch \
&& patch -p1 -d "$SP" --forward --fuzz=0 < /tmp/x264-threads-cap.patch \
&& patch -p1 -d "$SP" --forward --fuzz=0 < /tmp/pyav-scenecut.patch \
&& grep -q 'torch.compiler.load_cache_artifacts' "$SP/fastvideo/worker/gpu_worker.py" \
&& grep -q 'FASTVIDEO_X264_THREADS' "$SP/fastvideo/entrypoints/video_generator.py" \
&& grep -q 'FASTVIDEO_X264_SCENECUT' "$SP/fastvideo/entrypoints/video_generator.py" \
&& echo "patches applied + verified"

ENV FASTVIDEO_VIDEO_CODEC=libx264
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17 changes: 17 additions & 0 deletions examples/diffusers/patches/pyav-scenecut.patch
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@@ -0,0 +1,17 @@
diff --git a/fastvideo/entrypoints/video_generator.py b/fastvideo/entrypoints/video_generator.py
index bfc1633..ef4f213 100644
--- a/fastvideo/entrypoints/video_generator.py
+++ b/fastvideo/entrypoints/video_generator.py
@@ -1010,6 +1010,12 @@ class VideoGenerator:
video_stream.options = {
"preset": "ultrafast",
"tune": "zerolatency",
+ # Skip x264's scene-cut cost analysis: a pure encode-speed lever
+ # with no quality/compat effect for our fixed-GOP single-file
+ # output. Env-configurable (mirrors FASTVIDEO_X264_THREADS /
+ # FASTVIDEO_X264_PRESET below) so it's opt-out per model without
+ # a rebuild. Measured ~50-100ms/clip (deepinfra, 2026-07-07).
+ "x264-params": f"scenecut={os.getenv('FASTVIDEO_X264_SCENECUT', '0')}",
}

audio_stream = output.add_stream("aac", rate=sample_rate, layout=layout)
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