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I am trying to move a png image by 10px over a white background during 2s (fps=25), but the transition I got is not smooth.

Here is the command I am using:

ffmpeg -y -vsync passthrough -f lavfi -i color=c=white:size=300x250 -loop 1 -framerate 25 -i image.png -filter_complex "[0][1]overlay=eval=frame:format=yuv444:x=120:y=lerp(100\,110\,t/2)[s1]" -map "[s1]"  -c:v libx264 -t 2 video.mp4 -hide_banner -loglevel debug

At first I thought that all decimals were rounded to integers, but from what I see in the logs it seems that ffmpeg skips frames that contain a fraction of a pixel as a y coordinate (i.e. 100.2).

Here is the generated video & the log file.

Is there a way to generate a smooth effect?

1 Answer 1

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ffmpeg does not do sub-pixel overlay. Computed co-ordinates are truncated to integers.

The closest to getting a smooth result is to overlay a large PNG on a large background and then downscale the result to the final resolution i.e. [largebg][largefg]overlay=...,scale=300:250:flags=bicubic

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  • do you know if using overlay_cuda (gpu) supports sub-pixels?
    – antoox
    Nov 21 at 13:07
  • No, it does not.
    – Gyan
    Nov 21 at 17:44
  • I tried: Scaling by 4, but the result is blurry. Can you think of another way to get the best quality? ffmpeg -y -vsync 0 -f lavfi -i "color=c=white:size=300x250" -f lavfi -i "[email protected]:size=1200x1000,format=yuva420p" -loop 1 -i image.png -filter_complex "[2]scale=228:136[s0];[1][s0]overlay=eof_action=repeat:eval=frame:format=yuv444:x=480:y=lerp(400\,440\,t/2)[s1];[s1]scale=300x250:flags=bicubic[s2];[0][s2]overlay[s3]" -map "[s3]" -c:v libx264 -crf 0 -pix_fmt yuv420p -t 2 video_scale.mp4 -hide_banner
    – antoox
    Nov 21 at 19:22

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