Fixes to performance

gnommo/renderer.py

@@ -303,6 +303,11 @@ def build_ffmpeg_command(plan: RenderPlan, output_path: Path) -> list[str]:
     """Build the complete FFmpeg command as a list of arguments."""
     cmd = ["ffmpeg", "-y"]  # -y to overwrite output
 
+    # Global thread limits before any -i. Without this, each format=rgba conversion
+    # in the filter graph (one per video layer) spawns one swscaler thread per CPU core,
+    # causing OOM on Apple Silicon where av_cpu_count() returns 10-11.
+    cmd.extend(["-threads", "1", "-filter_threads", "1"])
+
     # Resolve paths to absolute
     project_path = plan.project_path.resolve()
     output_path = output_path.resolve()