Add GPU persistence mode and hardware decode support to streaming primitives

- Add CuPy integration for GPU-resident frame output
- Add NVDEC hardware decode detection and ffmpeg acceleration
- Configurable via STREAMING_GPU_PERSIST environment variable

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sexp_effects/primitive_libs/streaming.py

@@ -3,13 +3,53 @@ Streaming primitives for video/audio processing.
 
 These primitives handle video source reading and audio analysis,
 keeping the interpreter completely generic.
+
+GPU Acceleration:
+- Set STREAMING_GPU_PERSIST=1 to output CuPy arrays (frames stay on GPU)
+- Hardware video decoding (NVDEC) is used when available
+- Dramatically improves performance on GPU nodes
 """
 
+import os
 import numpy as np
 import subprocess
 import json
 from pathlib import Path
 
+# Try to import CuPy for GPU acceleration
+try:
+    import cupy as cp
+    CUPY_AVAILABLE = True
+except ImportError:
+    cp = None
+    CUPY_AVAILABLE = False
+
+# GPU persistence mode - output CuPy arrays instead of numpy
+# Disabled by default until all primitives support GPU frames
+GPU_PERSIST = os.environ.get("STREAMING_GPU_PERSIST", "0") == "1" and CUPY_AVAILABLE
+
+# Check for hardware decode support (cached)
+_HWDEC_AVAILABLE = None
+
+
+def _check_hwdec():
+    """Check if NVIDIA hardware decode is available."""
+    global _HWDEC_AVAILABLE
+    if _HWDEC_AVAILABLE is not None:
+        return _HWDEC_AVAILABLE
+
+    try:
+        result = subprocess.run(["nvidia-smi"], capture_output=True, timeout=2)
+        if result.returncode != 0:
+            _HWDEC_AVAILABLE = False
+            return False
+        result = subprocess.run(["ffmpeg", "-hwaccels"], capture_output=True, text=True, timeout=5)
+        _HWDEC_AVAILABLE = "cuda" in result.stdout
+    except Exception:
+        _HWDEC_AVAILABLE = False
+
+    return _HWDEC_AVAILABLE
+
 
 class VideoSource:
     """Video source with persistent streaming pipe for fast sequential reads."""
@@ -25,11 +65,20 @@ class VideoSource:
         self._last_read_time = -1
         self._cached_frame = None
 
+        # Check if file exists
+        if not self.path.exists():
+            raise FileNotFoundError(f"Video file not found: {self.path}")
+
         # Get video info
         cmd = ["ffprobe", "-v", "quiet", "-print_format", "json",
                "-show_streams", str(self.path)]
         result = subprocess.run(cmd, capture_output=True, text=True)
+        if result.returncode != 0:
+            raise RuntimeError(f"Failed to probe video '{self.path}': {result.stderr}")
+        try:
             info = json.loads(result.stdout)
+        except json.JSONDecodeError:
+            raise RuntimeError(f"Invalid video file or ffprobe failed: {self.path}")
 
         for stream in info.get("streams", []):
             if stream.get("codec_type") == "video":
@@ -46,30 +95,64 @@ class VideoSource:
                         self._duration = int(h) * 3600 + int(m) * 60 + float(s)
                 break
 
+        # Fallback: check format duration if stream duration not found
+        if self._duration is None and "format" in info and "duration" in info["format"]:
+            self._duration = float(info["format"]["duration"])
+
         if not self._frame_size:
             self._frame_size = (720, 720)
 
+        import sys
+        print(f"VideoSource: {self.path.name} duration={self._duration} size={self._frame_size}", file=sys.stderr)
+
     def _start_stream(self, seek_time: float = 0):
-        """Start or restart the ffmpeg streaming process."""
+        """Start or restart the ffmpeg streaming process.
+
+        Uses NVIDIA hardware decoding (NVDEC) when available for better performance.
+        """
         if self._proc:
             self._proc.kill()
             self._proc = None
 
+        # Check file exists before trying to open
+        if not self.path.exists():
+            raise FileNotFoundError(f"Video file not found: {self.path}")
+
         w, h = self._frame_size
-        cmd = [
+
-            "ffmpeg", "-v", "quiet",
+        # Build ffmpeg command with optional hardware decode
+        cmd = ["ffmpeg", "-v", "error"]
+
+        # Use hardware decode if available (significantly faster)
+        if _check_hwdec():
+            cmd.extend(["-hwaccel", "cuda"])
+
+        cmd.extend([
             "-ss", f"{seek_time:.3f}",
             "-i", str(self.path),
             "-f", "rawvideo", "-pix_fmt", "rgb24",
             "-s", f"{w}x{h}",
             "-r", str(self.fps),  # Output at specified fps
             "-"
-        ]
+        ])
-        self._proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.DEVNULL)
+
+        self._proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
         self._stream_time = seek_time
 
-    def _read_frame_from_stream(self) -> np.ndarray:
+        # Check if process started successfully by reading first bit of stderr
-        """Read one frame from the stream."""
+        import select
+        import sys
+        readable, _, _ = select.select([self._proc.stderr], [], [], 0.5)
+        if readable:
+            err = self._proc.stderr.read(4096).decode('utf-8', errors='ignore')
+            if err:
+                print(f"ffmpeg error for {self.path.name}: {err}", file=sys.stderr)
+
+    def _read_frame_from_stream(self):
+        """Read one frame from the stream.
+
+        Returns CuPy array if GPU_PERSIST is enabled, numpy array otherwise.
+        """
         w, h = self._frame_size
         frame_size = w * h * 3
 
@@ -80,7 +163,12 @@ class VideoSource:
         if len(data) < frame_size:
             return None
 
-        return np.frombuffer(data, dtype=np.uint8).reshape((h, w, 3)).copy()
+        frame = np.frombuffer(data, dtype=np.uint8).reshape((h, w, 3)).copy()
+
+        # Transfer to GPU if persistence mode enabled
+        if GPU_PERSIST:
+            return cp.asarray(frame)
+        return frame
 
     def read(self) -> np.ndarray:
         """Read frame (uses last cached or t=0)."""
@@ -100,6 +188,9 @@ class VideoSource:
         seek_time = t
         if self._duration and self._duration > 0:
             seek_time = t % self._duration
+            # If we're within 0.1s of the end, wrap to beginning to avoid EOF issues
+            if seek_time > self._duration - 0.1:
+                seek_time = 0.0
 
         # Decide whether to seek or continue streaming
         # Seek if: no stream, going backwards (more than 1 frame), or jumping more than 2 seconds ahead
@@ -118,20 +209,59 @@ class VideoSource:
             self._start_stream(seek_time)
 
         # Skip frames to reach target time
+        skip_retries = 0
         while self._stream_time + self._frame_time <= seek_time:
             frame = self._read_frame_from_stream()
             if frame is None:
-                # Stream ended, restart from seek point
+                # Stream ended or failed - restart from seek point
+                import time
+                skip_retries += 1
+                if skip_retries > 3:
+                    # Give up skipping, just start fresh at seek_time
                     self._start_stream(seek_time)
+                    time.sleep(0.1)
                     break
+                self._start_stream(seek_time)
+                time.sleep(0.05)
+                continue
             self._stream_time += self._frame_time
+            skip_retries = 0  # Reset on successful read
 
-        # Read the target frame
+        # Read the target frame with retry logic
+        frame = None
+        max_retries = 3
+        for attempt in range(max_retries):
             frame = self._read_frame_from_stream()
+            if frame is not None:
+                break
+
+            # Stream failed - try restarting
+            import sys
+            import time
+            print(f"RETRY {self.path.name}: attempt {attempt+1}/{max_retries} at t={t:.2f}", file=sys.stderr)
+
+            # Check for ffmpeg errors
+            if self._proc and self._proc.stderr:
+                try:
+                    import select
+                    readable, _, _ = select.select([self._proc.stderr], [], [], 0.1)
+                    if readable:
+                        err = self._proc.stderr.read(4096).decode('utf-8', errors='ignore')
+                        if err:
+                            print(f"ffmpeg error: {err}", file=sys.stderr)
+                except:
+                    pass
+
+            # Wait a bit and restart
+            time.sleep(0.1)
+            self._start_stream(seek_time)
+
+            # Give ffmpeg time to start
+            time.sleep(0.1)
+
         if frame is None:
             import sys
-            print(f"NULL FRAME {self.path.name}: t={t:.2f} seek={seek_time:.2f}", file=sys.stderr)
+            raise RuntimeError(f"Failed to read video frame from {self.path.name} at t={t:.2f} after {max_retries} retries")
-            frame = np.zeros((h, w, 3), dtype=np.uint8)
         else:
             self._stream_time += self._frame_time
 
@@ -160,16 +290,27 @@ class AudioAnalyzer:
         self.path = Path(path)
         self.sample_rate = sample_rate
 
+        # Check if file exists
+        if not self.path.exists():
+            raise FileNotFoundError(f"Audio file not found: {self.path}")
+
         # Load audio via ffmpeg
-        cmd = ["ffmpeg", "-v", "quiet", "-i", str(self.path),
+        cmd = ["ffmpeg", "-v", "error", "-i", str(self.path),
                "-f", "f32le", "-ac", "1", "-ar", str(sample_rate), "-"]
         result = subprocess.run(cmd, capture_output=True)
+        if result.returncode != 0:
+            raise RuntimeError(f"Failed to load audio '{self.path}': {result.stderr.decode()}")
         self._audio = np.frombuffer(result.stdout, dtype=np.float32)
+        if len(self._audio) == 0:
+            raise RuntimeError(f"Audio file is empty or invalid: {self.path}")
 
         # Get duration
         cmd = ["ffprobe", "-v", "quiet", "-print_format", "json",
                "-show_format", str(self.path)]
-        info = json.loads(subprocess.run(cmd, capture_output=True, text=True).stdout)
+        result = subprocess.run(cmd, capture_output=True, text=True)
+        if result.returncode != 0:
+            raise RuntimeError(f"Failed to probe audio '{self.path}': {result.stderr}")
+        info = json.loads(result.stdout)
         self.duration = float(info.get("format", {}).get("duration", 60))
 
         # Beat detection state
@@ -302,3 +443,20 @@ def prim_audio_beat_count(analyzer: AudioAnalyzer, t: float) -> int:
 def prim_audio_duration(analyzer: AudioAnalyzer) -> float:
     """Get audio duration in seconds."""
     return analyzer.duration
+
+
+# Export primitives
+PRIMITIVES = {
+    # Video source
+    'make-video-source': prim_make_video_source,
+    'source-read': prim_source_read,
+    'source-skip': prim_source_skip,
+    'source-size': prim_source_size,
+
+    # Audio analyzer
+    'make-audio-analyzer': prim_make_audio_analyzer,
+    'audio-energy': prim_audio_energy,
+    'audio-beat': prim_audio_beat,
+    'audio-beat-count': prim_audio_beat_count,
+    'audio-duration': prim_audio_duration,
+}