vibe coded that cool box blur btw
_ Explanation of Positioning:

(in_w-500)/2+10 _ crops 500px wide and shifts it 10 pixels to the right from center

(W-500)/2+10 _ overlays the blurred strip in the exact same spot


> This gives you a box that's still mostly centered but nudged slightly to the right to line up precisely over the watermark.
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_ Optional: Red Box for Preview

You can preview the position visually using:

ffmpeg -i input.mp4 -vf "drawbox=x=(iw-500)/2+10:y=900:w=500:h=80:color=red@0.7:t=fill" -c:a copy output_debug.mp4


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Let me know if you also want to fade the blur in/out, round the corners, or add a caption over it!