[FFmpeg-user] v360 / perspective

[Michael Koch]

Am 01.12.2020 um 19:56 schrieb Michael Koch:
> Hello,
>
> there seem to be some problems in the v360 filter with "perspective" 
> output.
> Tested with the latest Windows built, 2 days old. You can reproduce 
> this with any equirectangular input image.
>
> ffmpeg -i equirectangular_test.png -lavfi v360=e:perspective -y out1.png
>
> The output of the above command has two problems:
> -- The center of the input image is not mapped to the center of the 
> output image. For most other projections the image center is preserved.
> -- The output is mirror reversed (which means you cannot read text).
>
> Both problems can be corrected with this workaround:
>
> ffmpeg -i equirectangular_test.png -lavfi 
> v360=e:perspective:pitch=90:v_flip=1 -y out2.png
>
> Now I want to add a yaw rotation after the pitch rotation:
>
> ffmpeg -i equirectangular_test.png -lavfi 
> v360=e:perspective:rorder=pyr:pitch=90:yaw=20:v_flip=1 -y out3.png
>
> But in the output you can see that a roll rotation was done.

Today I did for the very first time figure out how to compile ffmpeg.
The above problem can be solved by changing two lines in vf_v360.c
Sorry, I haven't yet figured out how to use git.One thing after the 
other...

Old version:
line 3136:   vec[1] = sin_theta;
line 3137: vec[2] = cos_theta * cos_phi;

New version:
line 3136: vec[1] = cos_theta * cos_phi;
line 3137: vec[2] = sin_theta;

I'm not sure if lines 3139 to 3141 must also be changed.

Michael