diff --git a/examples/diffusers/Dockerfile.dreamverse b/examples/diffusers/Dockerfile.dreamverse
index 55495245a219..68c274771f9a 100644
--- a/examples/diffusers/Dockerfile.dreamverse
+++ b/examples/diffusers/Dockerfile.dreamverse
@@ -54,7 +54,7 @@ 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
+COPY patches/pyav-x264-tuning.patch /tmp/pyav-x264-tuning.patch
 COPY patches/flash-attn-cute-fa4-tuple-fix.patch /tmp/flash-attn-cute-fa4-tuple-fix.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
@@ -62,7 +62,7 @@ COPY patches/flash-attn-cute-fa4-tuple-fix.patch /tmp/flash-attn-cute-fa4-tuple-
 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 "$SP" --forward --fuzz=0 < /tmp/pyav-scenecut.patch \
+ && patch -p1 -d "$SP" --forward --fuzz=0 < /tmp/pyav-x264-tuning.patch \
  && patch -p1 -d "$SP" --forward --fuzz=0 < /tmp/flash-attn-cute-fa4-tuple-fix.patch \
  && grep -q 'torch.compiler.load_cache_artifacts' "$SP/fastvideo/worker/gpu_worker.py" \
  && grep -q 'FASTVIDEO_X264_THREADS' "$SP/fastvideo/entrypoints/video_generator.py" \
diff --git a/examples/diffusers/patches/pyav-scenecut.patch b/examples/diffusers/patches/pyav-x264-tuning.patch
similarity index 58%
rename from examples/diffusers/patches/pyav-scenecut.patch
rename to examples/diffusers/patches/pyav-x264-tuning.patch
index 79d003e5d7ab..b2fd35ef6bc3 100644
--- a/examples/diffusers/patches/pyav-scenecut.patch
+++ b/examples/diffusers/patches/pyav-x264-tuning.patch
@@ -2,7 +2,7 @@ diff --git a/fastvideo/entrypoints/video_generator.py b/fastvideo/entrypoints/vi
 index bfc1633..ef4f213 100644
 --- a/fastvideo/entrypoints/video_generator.py
 +++ b/fastvideo/entrypoints/video_generator.py
-@@ -1010,6 +1010,12 @@ class VideoGenerator:
+@@ -1010,6 +1010,20 @@ class VideoGenerator:
              video_stream.options = {
                  "preset": "ultrafast",
                  "tune": "zerolatency",
@@ -12,6 +12,14 @@ index bfc1633..ef4f213 100644
 +                # 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')}",
++                # Cap x264 threads. B200 has no NVENC so this is CPU libx264;
++                # unbounded, x264 auto-detects all node cores (~288) -> thread
++                # thrash. Isolated encode-only sweep (deepinfra 2026-07-09, 121f
++                # 1080p) bottoms out ~10-12 threads (~0.42s) and gets WORSE past
++                # 16 (0.64s+); 12 = sweet spot AND well under a fair share. The
++                # ffmpeg-pipe path caps at 32 but is dead on B200 (no ffmpeg on
++                # PATH). Env-configurable, no rebuild to change.
++                "threads": os.getenv("FASTVIDEO_X264_THREADS_PYAV", "12"),
              }
  
              audio_stream = output.add_stream("aac", rate=sample_rate, layout=layout)