diff --git a/gnommo/preprocessor.py b/gnommo/preprocessor.py
index 442abca..66cb5bc 100644
--- a/gnommo/preprocessor.py
+++ b/gnommo/preprocessor.py
@@ -19,7 +19,7 @@ from .models import (
 from typing import Union, Optional
 
 # Number of parallel workers for chunk processing
-DEFAULT_CHUNK_WORKERS = 4
+DEFAULT_CHUNK_WORKERS = 1
 
 # Chunk duration in seconds for parallel filter processing (avoids huge intermediate files)
 CHUNK_DURATION = 60
@@ -770,16 +770,17 @@ def apply_combined_video_filters(
 
     # Build FFmpeg command
     cmd = ["ffmpeg", "-y"]
+    # Global options before -i (after -i they become output options and don't limit filter threads)
+    cmd.extend(["-threads", "1", "-filter_threads", "1"])
 
     if take is not None:
         cmd.extend(["-t", str(take)])
 
     cmd.extend(
         [
+            "-probesize", "50000000", "-analyzeduration", "50000000",
             "-i",
             str(input_path),
-            "-filter_threads",
-            "1",
             "-vf",
             video_filter,
             "-c:v",
@@ -887,7 +888,9 @@ def build_mask_filter(config: dict) -> str:
     alpha_expr = "+".join(conditions)
     alpha_expr = f"if({alpha_expr},0,alpha(X,Y))"
 
-    return f"geq=lum='lum(X,Y)':cb='cb(X,Y)':cr='cr(X,Y)':a='{alpha_expr}'"
+    # Use r/g/b passthrough so this works in rgba space (as output by gnommokey/color_grade)
+    # without triggering an rgba→yuv conversion that would spawn 11 more swscaler threads.
+    return f"geq=r='r(X,Y)':g='g(X,Y)':b='b(X,Y)':a='{alpha_expr}'"
 
 
 def build_color_grade_filter(config: dict) -> str:
@@ -1140,8 +1143,9 @@ def build_gnommokey_filter(config: dict) -> str:
             parts.append(f"alphaextract,avgblur=sizeX={radius}:sizeY={radius}[blur]")
             # This gets complex - for now, skip alpha blur and just use erosion
 
-    # Ensure output is in a good format
-    parts.append("format=yuva444p10le")
+    # Stay in rgba so downstream filters (color_grade, mask) don't trigger
+    # a redundant yuva444p10le→rgba round-trip and its 11-thread swscaler call.
+    # The caller (_process_chunk_to_prores4444) appends format=yuva444p10le at the end.
 
     return ",".join(parts)
 
@@ -1353,10 +1357,20 @@ def _process_chunk_to_prores4444(
     # Build FFmpeg command
     cmd: list[str] = ["ffmpeg", "-y"]
 
+    # Global thread limits MUST be before the first -i.
+    # After -i they become output-stream options and FFmpeg ignores them for the
+    # filter graph — each geq stage then spawns one thread per CPU core (11 on M-series),
+    # causing the N-way RGBA frame buffer explosion that OOM-kills the process.
+    cmd.extend(["-threads", "1", "-filter_threads", "1"])
+
     # Seek to start time (before input for fast seeking)
     if start_time > 0:
         cmd.extend(["-ss", str(start_time)])
 
+    # Limit initial file analysis to 50 MB. Without this, FFmpeg scans the entire
+    # source file when moov is at the end (common for camera recordings), which reads
+    # gigabytes of data and triggers OOM when multiple chunk workers run in parallel.
+    cmd.extend(["-probesize", "50000000", "-analyzeduration", "50000000"])
     cmd.extend(["-i", str(input_path)])
 
     # Limit duration
@@ -1364,13 +1378,8 @@ def _process_chunk_to_prores4444(
     if actual_take is not None:
         cmd.extend(["-t", str(actual_take)])
 
-    # Video encode: ProRes 4444 with alpha
-    # -filter_threads 1: geq is serial anyway; limiting threads eliminates the N-way
-    # RGBA frame buffer explosion that causes OOM when chunk workers run in parallel.
     cmd.extend(
         [
-            "-filter_threads",
-            "1",
             "-vf",
             video_filter,
             "-c:v",
@@ -1682,10 +1691,9 @@ def apply_chroma_key(
 
     # Build FFmpeg command
     # ProRes 4444 profile for alpha channel support
-    cmd = [
-        "ffmpeg",
-        "-y",  # Overwrite output
-    ]
+    cmd = ["ffmpeg", "-y"]
+    # Global options before -i
+    cmd.extend(["-threads", "1", "-filter_threads", "1"])
 
     # Add duration limit if specified (before input for efficiency)
     if take is not None:
@@ -1695,8 +1703,6 @@ def apply_chroma_key(
         [
             "-i",
             str(input_path),
-            "-filter_threads",
-            "1",
             "-vf",
             video_filter,
             "-c:v",
@@ -1786,14 +1792,13 @@ def apply_mask(
     # Using: if(condition, 0, alpha(X,Y))
     alpha_expr = f"if({alpha_expr},0,alpha(X,Y))"
 
-    # Build the geq filter - preserve luma, chroma, modify alpha
-    video_filter = f"geq=lum='lum(X,Y)':cb='cb(X,Y)':cr='cr(X,Y)':a='{alpha_expr}'"
+    # Build the geq filter - preserve RGB channels, modify alpha
+    video_filter = f"geq=r='r(X,Y)':g='g(X,Y)':b='b(X,Y)':a='{alpha_expr}'"
 
     # Build FFmpeg command
-    cmd = [
-        "ffmpeg",
-        "-y",  # Overwrite output
-    ]
+    cmd = ["ffmpeg", "-y"]
+    # Global options before -i
+    cmd.extend(["-threads", "1", "-filter_threads", "1"])
 
     if take is not None:
         cmd.extend(["-t", str(take)])
@@ -1802,8 +1807,6 @@ def apply_mask(
         [
             "-i",
             str(input_path),
-            "-filter_threads",
-            "1",
             "-vf",
             video_filter,
             "-c:v",
diff --git a/gnommo/renderer.py b/gnommo/renderer.py
index 3f7e76a..a2a864a 100644
--- a/gnommo/renderer.py
+++ b/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()