Adding chunking to main render loop

gnommo/cache.py

@@ -49,6 +49,28 @@ def get_ffmpeg_thread_count() -> int:
     return max(1, int(cpu_count * cpu_limit))
 
 
+def get_render_chunk_size() -> Optional[int]:
+    """Return slides-per-chunk for auto-chunked rendering, or None if not configured.
+
+    When set, cmd_render splits the filter graph into chunks of this many slides
+    to avoid OOM from allocating filter buffers for the entire video at once.
+
+    Example ~/.gnommo.conf:
+        [performance]
+        render_chunk_slides = 15
+    """
+    global _perf_config
+    if _perf_config is None:
+        get_ffmpeg_thread_count()  # populates _perf_config
+    val = _perf_config.get("render_chunk_slides")
+    if val is None:
+        return None
+    try:
+        return max(1, int(val))
+    except (ValueError, TypeError):
+        return None
+
+
 def load_cache_config() -> Optional[Path]:
     """Load gnommo.conf and return cache path if configured.
 

gnommo/cli.py

@@ -133,6 +133,13 @@ Examples:
         type=str,
         help="Render only a range of slides (e.g., S1:S10, S5:, S10:S20)",
     )
+    parser.add_argument(
+        "--chunk-slides",
+        type=int,
+        default=0,
+        dest="chunk_slides",
+        help="Split render into chunks of N slides each and concatenate (overrides render_chunk_slides in .gnommo.conf)",
+    )
     parser.add_argument(
         "--res",
         type=str,
@@ -261,6 +268,7 @@ Examples:
                 args.slides,
                 args.res,
                 args.force,
+                chunk_slides=args.chunk_slides,
             )
         elif action == "transcribe":
             return cmd_transcribe(project_path, args.verbose, args.res, args.final)
@@ -2441,6 +2449,90 @@ def _writeback_video_metadata(plan, project_path, config) -> None:
         print(f"  Updated videos.json: {written}")
 
 
+def _chunked_render(
+    project_path: Path,
+    verbose: bool,
+    dry_run: bool,
+    res: str,
+    force: bool,
+    chunk_size: int,
+    slide_ids: list[str],
+    out_dir: Path,
+    final_output: Path,
+) -> int:
+    """Render in slide-based chunks then concatenate — avoids filter graph OOM."""
+    import math
+
+    # Split slide IDs into groups of chunk_size
+    groups = [slide_ids[i : i + chunk_size] for i in range(0, len(slide_ids), chunk_size)]
+    print(
+        f"\n  Auto-chunking: {len(slide_ids)} slides → {len(groups)} chunks of ≤{chunk_size}"
+    )
+
+    chunks_dir = out_dir / "chunks"
+    chunks_dir.mkdir(parents=True, exist_ok=True)
+
+    chunk_paths: list[Path] = []
+    for i, group in enumerate(groups):
+        start = group[0]
+        end = groups[i + 1][0] if i + 1 < len(groups) else None
+        slides_arg = f"{start}:{end}" if end else f"{start}:"
+        chunk_path = chunks_dir / f"chunk_{i+1:03d}_{start}-{end or 'end'}.mp4"
+
+        print(f"\n  {'='*56}")
+        print(f"  Chunk {i+1}/{len(groups)}: {slides_arg} → {chunk_path.name}")
+        print(f"  {'='*56}")
+
+        result = cmd_render(
+            project_path,
+            verbose,
+            dry_run,
+            slides_arg=slides_arg,
+            res=res,
+            force=force,
+            _output_path_override=chunk_path,
+        )
+        if result != 0:
+            print(f"\n  Chunk {i+1} failed — aborting.", file=sys.stderr)
+            return result
+        chunk_paths.append(chunk_path)
+
+    if dry_run:
+        print(f"\n  [dry-run] Would concatenate {len(chunk_paths)} chunks → {final_output}")
+        return 0
+
+    # Concatenate chunks
+    print(f"\n  Concatenating {len(chunk_paths)} chunks → {final_output.name}...")
+    concat_list = chunks_dir / "concat.txt"
+    with open(concat_list, "w") as f:
+        for p in chunk_paths:
+            f.write(f"file '{p.resolve()}'\n")
+
+    concat_cmd = [
+        "ffmpeg", "-y",
+        "-f", "concat", "-safe", "0",
+        "-i", str(concat_list),
+        "-c", "copy",
+        str(final_output),
+    ]
+    result = subprocess.run(concat_cmd, capture_output=True, text=True)
+    if result.returncode != 0:
+        print(f"  Concatenation failed:\n{result.stderr}", file=sys.stderr)
+        return 1
+
+    # Clean up chunk files
+    for p in chunk_paths:
+        p.unlink(missing_ok=True)
+    concat_list.unlink(missing_ok=True)
+    try:
+        chunks_dir.rmdir()
+    except OSError:
+        pass
+
+    print(f"  Output: {final_output}")
+    return 0
+
+
 def cmd_render(
     project_path: Path,
     verbose: bool,
@@ -2448,6 +2540,8 @@ def cmd_render(
     slides_arg: str = None,
     res: str = "full",
     force: bool = False,
+    chunk_slides: int = 0,
+    _output_path_override: Path = None,
 ) -> int:
     """Render final video."""
     from .parser import (
@@ -2702,17 +2796,35 @@ def cmd_render(
 
     # Stage 4: Render
     # Determine output filename and directory
-    if config.output_video:
+    if _output_path_override:
+        output_path = _output_path_override
+        out_dir = output_path.parent
+        out_filename = output_path.name
+    elif config.output_video:
         out_filename = config.output_video
+        out_dir = project_path / "out" / res if res != "full" else project_path / "out"
+        output_path = out_dir / out_filename
     elif slide_range:
         start, end = slide_range
         range_suffix = f"_{start}-{end}" if end else f"_{start}-end"
         out_filename = f"final{range_suffix}.mp4"
-    else:
-        out_filename = f"{config.co}.mp4"
-
         out_dir = project_path / "out" / res if res != "full" else project_path / "out"
         output_path = out_dir / out_filename
+    else:
+        out_filename = f"{config.co}.mp4"
+        out_dir = project_path / "out" / res if res != "full" else project_path / "out"
+        output_path = out_dir / out_filename
+
+    # Check if chunked rendering is needed (avoids filter graph OOM on long videos)
+    from .cache import get_render_chunk_size
+    _chunk_size = chunk_slides or get_render_chunk_size() or 0
+    _slide_ids = [e.slide_id for e in plan.slide_events]
+    if _chunk_size > 0 and not slide_range and len(_slide_ids) > _chunk_size:
+        return _chunked_render(
+            project_path, verbose, dry_run, res, force,
+            _chunk_size, _slide_ids, out_dir, output_path,
+        )
+
     plan.output_path = output_path
 
     if dry_run: