Animated WebP resize doesn't keep loop and delay

[georgiopandarez]

Hi,

When resizing an animation (webp or gif), metadata is lost and the resulting image is not animated. Converting animation without resizing works fine. Tested against debian libvips42 and latest master.

• vipsthumbnail -s 200x200 -o /tmp/gif.webp samples/animated.gif

• vipsheader -a /tmp/gif.webp
  /tmp/gif.webp: 200x116 uchar, 3 bands, srgb, webpload
  width: 200
  height: 116
  bands: 3
  format: uchar
  coding: none
  interpretation: srgb
  xoffset: 0
  yoffset: 0
  xres: 1
  yres: 1
  filename: /tmp/gif.webp
  vips-loader: webpload

[jcupitt]

Hello @georgiopandarez,

By default, it'll just process the first frame -- you need to ask for all frames. Try:

vipsthumbnail something.gif[n=-1] -s 200x200 -o x.gif

You can use page= and n= to select a range of pages in the image to thumbnail. n=-1 means all pages.

[georgiopandarez]

Hi!

Thanks for the prompt reply. The issue seems to be when resizing and converting. ie

vipsthumbnail something.gif[n=-1] -s 200x200 -o x.webp

This results in an image with no animation.

The below python also shows issues:

image = pyvips.Image.gifload(sys.argv[1], access="sequential", n=-1)
dim = int(sys.argv[2])
resized_image = image.resize(dim / image.width, vscale=dim / image.height)
resized_image.webpsave(sys.argv[1] + ".webp")
image.webpsave(sys.argv[1] + ".noresize.webp")

The resized webp version shows a single image with the frames on top of each other. The resave shows an image without animation. Does one need to manually calculate page_height?

[jcupitt]

It should work, I think. With this GIF:

If I run:

vipsthumbnail dancing-banana.gif[n=-1] -s 200 -o x.webp

I get an animation that plays correctly in chrome (I'd attach it, but github does not allow webp). Do you have an example that fails?

Yes, you have to adjust page-height yourself. thumbnail has extra logic to do this for you.

It's best to use thumbnail if you can -- it also knows about webp shrink-on-load, so it should be much faster than resize.

[georgiopandarez]

Sorry to waste your time.

My code issue was that image.height returns the height of the image * the number of pages. I needed to take that into account when resizing.

I tried to verify using vipsthumbnail but missed that -o placed the image in the same directory as the input, not relative to the program.

[jcupitt]

Yes, it's relative to the input, so you can do eg.:

vipsthumbnail */*.jpg -o %s-thumbnail.jpg

It's more like a pattern for the output path than a standard -o switch. Anyway, glad it's working.