Rendering: The same Ass script using the \blur tag performs abnormally on the Android platform, but on iOS

[chenyangxx]

Rendering: The same Ass script using the \blur tag performs abnormally on the Android platform, but on iOS

[astiob]

libass only outputs alpha masks and doesn’t blend them onto the video itself; the video player does that. Our calculations for blur are exactly the same on all platforms; at most, we have differently accelerated versions of the code for different CPUs, but we verify that they produce the same output. I suspect that your Android video renderer does something wrong when it blends the alpha masks onto the video, although I’m afraid I can’t say what exactly is wrong just from looking at the picture.

If there were many layers stacked on top of each other, it would be normal to see banding if each layer is blended without dithering, e. g. as pictured in #442, but again this should happen on all platforms. (This can be avoided by blending in floating point or applying random dithering. But this doesn’t seem to be your issue anyway.)

The two pictures in the report show different subtitles and (also important for blending) different videos, and the bad case’s ASS isn’t shown, so I also can’t completely rule out (based on these samples alone) the possibility that there’s some problem with that particular sample’s ASS, after all, although I trust you that you’ve verified this before filing the report. At the very least, the ASS does seem to differ: one sample has underline but the other doesn’t, and the size or resolution seems different too.