qimage producer issue with webp images

[ShrugerXu]

Hello,

I'm having issue compositing webp images, the second webp image of a track ("2_webp_ll.webp", shows up at approximately the 4th second of the output video mentioned below) becomes a white chunk under Ubuntu while normal under Windows, here are my melt commands:
Ubuntu (melt 7.28.0 docker image):

/usr/bin/dumb-init -- /usr/bin/xvfb-run -a /usr/local/bin/melt -producer color:red out=500 -track -producer 1_webp_a.webp in=0 out=100 -producer 2_webp_ll.webp in=100 out=200 -transition composite -consumer avformat:test_linux_28.mp4 out=300

Windows (using melt.exe from Shotcut-240913):

melt.exe -producer color:red out=500 -track -producer 1_webp_a.webp in=0 out=100 -producer 2_webp_ll.webp in=100 out=200 -transition composite -consumer avformat:test_win.mp4 out=300

At first I thought it was because of different qimage version between the two os, so I tried to build melt using qt6 under Ubuntu 24, but it turned out the same, white chunk still appeared.

I'm confused why there is such a difference, any advice would be very grateful.

images I use:
images.zip

output:

Linux
https://github.com/user-attachments/assets/50085ec2-2b22-4753-b565-ba9c85c31358

WIndows
https://github.com/user-attachments/assets/99d322e2-b7ce-481d-9833-c090e85fc664

"white chunk" screenshot
https://github.com/user-attachments/assets/44915c63-df6f-46d9-9b23-76044a47059a

[bmatherly]

I performed a quick test on my Ubuntu 20.04.6 machine.

Here is what I did:

1. Download the shotcut portable zip from the shotcut website
2. Download your images linked above
3. Run the command (copied from your docker command):
   melt -producer color:red out=500 -track -producer 1_webp_a.webp in=0 out=100 -producer 2_webp_ll.webp in=100 out=200 -transition composite -consumer avformat:test_linux_28.mp4 out=300

The resulting file correctly showed the penguin image at 4 seconds (no white chunk).

You are correct that we use Qt to decode the webp file. Maybe there is still a difference in the versions we are using.

You could try running the Shotcut portable melt command in your docker image as a test to rule out the environment.

[ShrugerXu]

Using shotcut portable works, I will do further version comparison.

Thank you very much!