After Effects Gaussian Blur Causing Mobile Lag + Safari Alpha Flicker

[snappy11]

Guys, I’m editing a hero video in After Effects for a client’s website (spotifydescargar.org), and I’m stuck with two weird AE-specific issues.

First: The Gaussian Blur effect (applied to the background) makes the video lag like crazy on mobile (iOS/Android). If I remove the blur, it’s smooth, but the client wants it. Tried pre-rendering ProRes with alpha, lowering samples, GPU acceleration… no luck.

Second: The semi-transparent overlay (using Multiply blending mode) flickers with random pixels in Safari (desktop/mobile). Works fine in Chrome/Firefox. Tried Straight Alpha vs Premultiplied, Solid Composite effect, even PNG sequences—still flickers.

When I export via AME (H.265), the file is 50MB (needs to be <5MB). Render Queue H.264 breaks the alpha. Searched YouTube for “AE blur lag mobile” and “Safari alpha flicker AE”… only found basic fixes I already tried.

Is this a known AE bug? Should I switch to Camera Lens Blur or ditch blending modes? Client’s deadline is tomorrow. 😞

[nishu_kush · Accepted solution]

Hi Snappy11,

I don't think it is an issue with After Effects, but I'd love to investigate. It could be related to the player in the iOS/Android device. Can you try using a different player? The same goes for the browser. If possible, please share the files with me so that I can test them on my end.

You can lower the resolution and bit rate to decrease the size of the exported file, but that'll also lower the quality. Also, H.264 doesn't support alpha. If you want transparency in your video, you may want to use a different format. ProRes 4444 for example. 

Looking forward to your response. 

Thanks,
Nishu