Adding deque to avoid large amounts of memory used to hold log output

gnommo/preprocessor.py

@@ -332,8 +332,17 @@ def set_ffmpeg_loglevel(level: Optional[str]) -> None:
 
 
 def run_ffmpeg_with_progress(cmd, duration, description="Processing", loglevel=None):
+    from collections import deque
+
     cmd = cmd.copy()
 
+    # Retain only a bounded tail of FFmpeg's output. FFmpeg emits a -progress block
+    # every second (plus any per-frame warnings), so on a long or stuck-at-99% run an
+    # unbounded list grows in Python until it eats all RAM — which is what OOM'd the
+    # 66 GB render box while ffmpeg sat at the last frame. The last N lines are all
+    # the error path ever needs.
+    _LOG_TAIL = 5000
+
     # Explicit call arg wins, else the module-level setting, else the quiet bar.
     level = loglevel if loglevel is not None else _FFMPEG_LOGLEVEL
     stream = level is not None
@@ -349,7 +358,7 @@ def run_ffmpeg_with_progress(cmd, duration, description="Processing", loglevel=N
             cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT,
             text=True, bufsize=1, universal_newlines=True,
         )
-        logs = []
+        logs = deque(maxlen=_LOG_TAIL)
         for line in iter(p.stdout.readline, ""):
             logs.append(line)
             sys.stdout.write(line)
@@ -384,7 +393,7 @@ def run_ffmpeg_with_progress(cmd, duration, description="Processing", loglevel=N
     last_percent = 0
     seen_any_progress = False
     last_log_line = ""
-    logs = []
+    logs = deque(maxlen=_LOG_TAIL)
 
     def draw(percent, suffix=""):
         filled = int(bar_width * percent / 100)