v360 filter with alpha_mask and dfisheye output

[Michael Koch]

There is a small bug in the v360 filter with dfisheye output if the alpha_mask=1 option is used. A vertical line in the left half is made transparent.
In this example I'm filling the transparent pixels with red color to show the problem:

ffmpeg -f lavfi -i color=white:s=800x400 -f lavfi -i color=red:s=800x400 -lavfi [0]v360=e:dfisheye:alpha_mask=1[a],[1][a]overlay -frames 1 -y out.png

Suggestion for improvement: For fisheye and dfisheye output, there should be an option to make the output circular and fill the outer area transparent. In most cases the outer area of the circle is not required, and it might become faster.

[Elon Musk]

not a bug

[Michael Koch]

I don't know why, but the bug has disappeared now.
My suggestion for improvement is still valid. The workaround is to overlay a circular mask. But it's uneffective to calculate the outer area and then mask it away.