6

I'm trying to create a basic 5 second zoompan to the center of an image (from the example on the ffmpeg.org website). The command below works, but jitters more than my hands after 5 cups of coffee:

ffmpeg -framerate 25 -loop 1 -i island.jpg -filter_complex "[0:v]scale=-2:480,zoompan=z='min(zoom+0.0015,1.5)':x='iw/2-(iw/zoom/2)':y='ih/2-(ih/zoom/2)':d=125,trim=duration=5[v]" -map "[v]" -y out.mp4

Input jpg. Output mp4.

I'm aware of the ffmpeg bug #4298. The posted suggested workaround is to use the scale filter prior to zoompan. But as shown in my example, this still seems to have no effect.

It seems any arbitrary x or y values cause the jiggle/jerky/shaky effect.

Can anyone offer any kind of effective workaround? Thanks!

Version info:

ffmpeg version 3.1.2-static http://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2016 the FFmpeg developers
  built with gcc 5.4.0 (Debian 5.4.0-6) 20160609
13

Avoid downscaling beforehand. Either apply a trunc function to the x and y expressions. Or upscale it before. Preferably the latter. This gets rid of most of the jitter for me.

ffmpeg -framerate 25 -loop 1 -i island.jpg -filter_complex "[0:v]scale=8000x4000,zoompan=z='min(zoom+0.0015,1.5)':x='iw/2-(iw/zoom/2)':y='ih/2-(ih/zoom/2)':d=125,trim=duration=5[v]" -map "[v]" -y out.mp4

Basically, the filter is rounding the values from the x and y expressions, which may be either rounded up or down. That's creating an uneven motion due to changes in direction of pan. Increasing the resolution beforehand allows the rounding to be smaller.

  • 1
    Awesome, thank you! I was also able to the downscale after the zoompan filter to get the desired 480p and the zoom remained smooth: ffmpeg -framerate 25 -loop 1 -i island.jpg -filter_complex "[0:v]scale=8000x4000,zoompan=z='min(zoom+0.0015,1.5)':x='iw/2-(iw/zoom/2)':y='ih/2-(ih/zoom/2)':d=125,trim=duration=5[v1];[v1]scale=-2:480[v]" -map "[v]" -y out.mp4 – Timbo White Aug 12 '16 at 8:24
  • You can scale the output from within zoompan e..g :d=125:s=hd480 or d=125:s=640x360 – Gyan Aug 12 '16 at 10:24
  • OK so s is zoompan's output image size. But it doesn't seem like there's a way to get zoompan's scale to preserve the aspect ratio of the original image automatically. So in order to get the result to a height of 480 with aspect ratio preserved for this 4000x2000 example, you'd have manually set zoompan to s=960x480 (can't use -2x480 trick). Otherwise zoompan uses s=hd720 (1280x720) by default, which skews the aspect ratio. – Timbo White Aug 12 '16 at 10:57
  • @Mulvya, can you expand on "apply a trunc function to the x and y expressions" upscaling can cause a decrease in performance, maybe there is an alternative work around. – Eric Jan 26 '18 at 4:08
  • After the filter evaluates the x & y value for a given frame,trunc will remove the fractional part of the result. Apply it like this x=trunc(iw/2-(iw/zoom/2)). This may not be as smooth as the upscale route. – Gyan Jan 26 '18 at 4:33

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