diff --git a/scripts/subtitle.py b/scripts/subtitle.py
index fa4e1ae..5048cbe 100644
--- a/scripts/subtitle.py
+++ b/scripts/subtitle.py
@@ -261,6 +261,7 @@ Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
         "ffmpeg", "-y", "-i", str(video),
         "-vf", vf,
         "-c:v", "libx264", "-preset", "medium", "-crf", "21",
+        "-pix_fmt", "yuv420p",  # web/mobile compat (Instagram/FB/web players)
         "-c:a", "copy",
         "-movflags", "+faststart",
         str(output),