diff --git a/biz/ffmpeg.py b/biz/ffmpeg.py
index 13ad6e3..5b7dcd9 100644
--- a/biz/ffmpeg.py
+++ b/biz/ffmpeg.py
@@ -129,7 +129,9 @@ def check_placeholder_exist_with_count(placeholder_id, task_params, required_cou
     return False
 
 
-def start_ffmpeg_task(ffmpeg_task, max_workers=4):
+def start_ffmpeg_task(ffmpeg_task, max_workers=None):
+    if max_workers is None:
+        max_workers = int(os.environ.get("FFMPEG_MAX_WORKERS", 4))
     tracer = get_tracer(__name__)
     with tracer.start_as_current_span("start_ffmpeg_task") as span:
         sub_tasks = list(ffmpeg_task.analyze_input_render_tasks())