Problem with transparent videos on android

[icune]

Hello guys!
Great project, thank you for it!
Just found a bug and want to report him

Bug: On some Android phones there's issue with transparency when several VideoDecoders work in parrallel.
Video with bug on Pixel 8 Pro:
https://github.com/user-attachments/assets/84f0412d-8114-4735-a57a-e581dca23567

Demo you can launch and reproduce the bug: https://github.com/icune/mediabunny-bug

[Vanilagy]

What is the bug? What is the behavior that seems wrong?

[icune]

@Vanilagy bug is that there's discrepancy between two VideoDecoders of one video. Alpha mask is not taken from current frame, but from i +- x, where i - current frame number and x is unknown, but I think in range from 1 to 3

[Vanilagy]

Is this reproducible with all Android phones or just some? I have a Xiaomi 15 at home. Can you send me one of the fucky exported videos as well?

[romikzo]

Hi @Vanilagy! I'll answer for @icune. Here you have it: https://github.com/icune/mediabunny-bug/blob/master/app/src/public/video/heart.webm. I suppose it’s not just a single “lucky” sample. We can give you more samples, but our files were produced by ffmpeg converting them from WebP files, which makes me think all WebM files with transparency can experience this bug on Google Pixel and Redmi devices (maybe on other Android phones as well). If I remember correctly, this bug can be reproduced in one of the environments on BrowserStack (seems they even have an open‑source program).