10

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
Timbo White
  • 245
  • 1
  • 2
  • 9

1 Answers1

16

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.

Gyan
  • 34,439
  • 6
  • 56
  • 98
  • 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 08:24
  • 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 04:08
  • 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 04:33
  • 1
    It's been almost two years since the answer but the problem is still there, ffmpeg team did nothing in this part. If you want to do zoompan over 4k video and use this upscaling then you get a huge memory overhead and performance downgrade about 16x times on my machine. – Northern Captain Apr 04 '18 at 21:13
  • I'll take a look at the code. – Gyan Apr 05 '18 at 05:39
  • The issue is being tracked [here](https://trac.ffmpeg.org/ticket/4298) (reported by [@slhck](https://stackoverflow.com/users/435093/slhck)), but it hasn't received much love actually... the scaling workaround isn't always a solution as it uses a lot of memory – mcont Apr 25 '18 at 19:38