Add streaming video compositor with sexp interpreter

- New streaming/ module for real-time video processing:
  - compositor.py: Main streaming compositor with cycle-crossfade
  - sexp_executor.py: Executes compiled sexp recipes in real-time
  - sexp_interp.py: Full S-expression interpreter for SLICE_ON Lambda
  - recipe_adapter.py: Bridges recipes to streaming compositor
  - sources.py: Video source with ffmpeg streaming
  - audio.py: Real-time audio analysis (energy, beats)
  - output.py: Preview (mpv) and file output with audio muxing

- New templates/:
  - cycle-crossfade.sexp: Smooth zoom-based video cycling
  - process-pair.sexp: Dual-clip processing with effects

- Key features:
  - Videos cycle in input-videos order (not definition order)
  - Cumulative whole-spin rotation
  - Zero-weight sources skip processing
  - Live audio-reactive effects

- New effects: blend_multi for weighted layer compositing
- Updated primitives and interpreter for streaming compatibility

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

streaming/demo.py

@@ -0,0 +1,125 @@
+#!/usr/bin/env python3
+"""
+Demo script for streaming compositor.
+
+Usage:
+    # Preview two videos blended
+    python -m streaming.demo preview video1.mp4 video2.mp4
+
+    # Record output to file
+    python -m streaming.demo record video1.mp4 video2.mp4 -o output.mp4
+
+    # Benchmark (no output)
+    python -m streaming.demo benchmark video1.mp4 --duration 10
+"""
+
+import argparse
+import sys
+from pathlib import Path
+
+# Add parent to path for imports
+sys.path.insert(0, str(Path(__file__).parent.parent))
+
+from streaming import StreamingCompositor, VideoSource
+from streaming.output import NullOutput
+
+
+def demo_preview(sources: list, duration: float, effects: bool = False):
+    """Preview sources with optional simple effects."""
+    effects_config = None
+    if effects:
+        effects_config = [
+            [{"effect": "rotate", "angle": 15}],
+            [{"effect": "zoom", "amount": 1.2}],
+        ][:len(sources)]
+
+    compositor = StreamingCompositor(
+        sources=sources,
+        effects_per_source=effects_config,
+        recipe_dir=Path(__file__).parent.parent,
+    )
+    compositor.run(output="preview", duration=duration)
+
+
+def demo_record(sources: list, output_path: str, duration: float):
+    """Record blended output to file."""
+    compositor = StreamingCompositor(
+        sources=sources,
+        recipe_dir=Path(__file__).parent.parent,
+    )
+    compositor.run(output=output_path, duration=duration)
+
+
+def demo_benchmark(sources: list, duration: float):
+    """Benchmark processing speed (no output)."""
+    compositor = StreamingCompositor(
+        sources=sources,
+        recipe_dir=Path(__file__).parent.parent,
+    )
+    compositor.run(output="null", duration=duration)
+
+
+def demo_audio_reactive(sources: list, duration: float):
+    """Preview with live audio reactivity."""
+    from streaming.audio import AudioAnalyzer
+
+    # Create compositor with energy-reactive effects
+    effects_config = [
+        [{
+            "effect": "zoom",
+            "amount": {"_binding": True, "source": "live_energy", "feature": "values", "range": [1.0, 1.5]},
+        }]
+        for _ in sources
+    ]
+
+    compositor = StreamingCompositor(
+        sources=sources,
+        effects_per_source=effects_config,
+        recipe_dir=Path(__file__).parent.parent,
+    )
+
+    # Start audio analyzer
+    try:
+        with AudioAnalyzer() as audio:
+            print("Audio analyzer started. Make some noise!", file=sys.stderr)
+            compositor.run(output="preview", duration=duration, audio_analyzer=audio)
+    except Exception as e:
+        print(f"Audio not available: {e}", file=sys.stderr)
+        print("Running without audio...", file=sys.stderr)
+        compositor.run(output="preview", duration=duration)
+
+
+def main():
+    parser = argparse.ArgumentParser(description="Streaming compositor demo")
+    parser.add_argument("mode", choices=["preview", "record", "benchmark", "audio"],
+                        help="Demo mode")
+    parser.add_argument("sources", nargs="+", help="Video source files")
+    parser.add_argument("-o", "--output", help="Output file (for record mode)")
+    parser.add_argument("-d", "--duration", type=float, default=30,
+                        help="Duration in seconds")
+    parser.add_argument("--effects", action="store_true",
+                        help="Apply simple effects (for preview)")
+
+    args = parser.parse_args()
+
+    # Verify sources exist
+    for src in args.sources:
+        if not Path(src).exists():
+            print(f"Error: Source not found: {src}", file=sys.stderr)
+            sys.exit(1)
+
+    if args.mode == "preview":
+        demo_preview(args.sources, args.duration, args.effects)
+    elif args.mode == "record":
+        if not args.output:
+            print("Error: --output required for record mode", file=sys.stderr)
+            sys.exit(1)
+        demo_record(args.sources, args.output, args.duration)
+    elif args.mode == "benchmark":
+        demo_benchmark(args.sources, args.duration)
+    elif args.mode == "audio":
+        demo_audio_reactive(args.sources, args.duration)
+
+
+if __name__ == "__main__":
+    main()