[FFmpeg-user] multiple flat videos in a equirectangular projection - v360 filter

[Denis Połeć]

> Am 16.07.2022 um 22:12 schrieb Michael Koch <astroelectronic at t-online.de>:
> 
> Am 16.07.2022 um 20:57 schrieb Denis Połeć:
>> 
>>> Am 16.07.2022 um 11:46 schrieb Paul B Mahol <onemda at gmail.com>:
>>> 
>>> On Sat, Jul 16, 2022 at 11:22 AM Denis Połeć <denis.polec at gmail.com> wrote:
>>> 
>>>> Hello,
>>>> I wouldn't call myself a beginner, but I still need a little bit to become
>>>> a pro. :)
>>>> I have a question that might be easy to answer.
>>>> 
>>>> I am working on a script to bring multiple flat videos into a
>>>> equirectangular projection by using v360 filter.
>>>> I have the problem that the edges of the input are very jagged.
>>>> 
>>>> This did not lead to a good result when I play the equirectangular
>>>> projection in a 360 player. I have also already tried different
>>>> interpolation modes, which does not lead to a better result.
>>>> Does anyone have an idea how I can avoid that? Is there a better way to do
>>>> this task?
>>>> 
>>>> 
>>>> Here is an example code with the result. The video in the example has a
>>>> resolution of 1080p:
>>>> 
>>>> 
>>>> ffmpeg -i BRAIN.mp4 -lavfi "\
>>>> 
>>>> [0]v360=input=flat:output=e:id_fov=45:w=5120:h=2560:yaw='0':alpha_mask=1[fg1];\
>>>> 
>>>> [0]v360=input=flat:output=e:id_fov=45:w=5120:h=2560:yaw=90:alpha_mask=1[fg2];[fg2][fg1]overlay[a];\
>>>> 
>>>> [0]v360=input=flat:output=e:id_fov=45:w=5120:h=2560:yaw=-90:alpha_mask=1[fg3];[fg3][a]overlay[b];\
>>>> 
>>>> [0]v360=input=flat:output=e:id_fov=45:w=5120:h=2560:yaw=180:alpha_mask=1[fg4];[fg4][b]overlay[c];\
>>>> \
>>>> 
>>>> [0]v360=input=flat:output=e:id_fov=45:w=5120:h=2560:yaw=0:pitch=45:alpha_mask=1[fg5];[fg5][c]overlay[d];\
>>>> 
>>>> [0]v360=input=flat:output=e:id_fov=45:w=5120:h=2560:yaw=90:roll=45:alpha_mask=1[fg6];[fg6][d]overlay[e];\
>>>> 
>>>> [0]v360=input=flat:output=e:id_fov=45:w=5120:h=2560:yaw=-90:roll=-45:alpha_mask=1[fg7];[fg7][e]overlay[f];\
>>>> 
>>>> [0]v360=input=flat:output=e:id_fov=45:w=5120:h=2560:yaw=180:pitch=-45:alpha_mask=1[fg8];[fg8][f]overlay[g];\
>>>> \
>>>> 
>>>> [0]v360=input=flat:output=e:id_fov=45:w=5120:h=2560:yaw=0:pitch=-45:alpha_mask=1[fg9];[fg9][g]overlay[h];\
>>>> 
>>>> [0]v360=input=flat:output=e:id_fov=45:w=5120:h=2560:yaw=90:roll=-45:alpha_mask=1[fg10];[fg10][h]overlay[i];\
>>>> 
>>>> [0]v360=input=flat:output=e:id_fov=45:w=5120:h=2560:yaw=-90:roll=45:alpha_mask=1[fg11];[fg11][i]overlay[j];\
>>>> 
>>>> [0]v360=input=flat:output=e:id_fov=45:w=5120:h=2560:yaw=180:pitch=45:alpha_mask=1[fg12];[fg12][j]overlay[k];\
>>>> \
>>>> 
>>>> [0]v360=input=flat:output=e:id_fov=45:w=5120:h=2560:yaw=0:pitch=90:alpha_mask=1[fg13];[fg13][k]overlay[l];\
>>>> [0]drawbox=w=1:h=1:color=black,v360=input=flat:output=e:id_fov=45:w=5120:h=2560:yaw=0:pitch=-90:alpha_mask=1[fg14];[fg14][l]overlay"
>>>> -q:v 4 -vframes 1 -y test11.jpg
>>>> 
>>>> Your filtergraph is extremely inefficient with that many cascaded overlays
>>> and gives poor results. For proper stitching borders need to have small
>>> transition from full opacity to no opacity.
>>> 
>>> To add small transitions with opacity on borders could use blurring filters
>>> for example on alpha plane only.
>> How could I achieve that? How can I blurry just the borders?
> 
> You could apply some preprocessing to your input video, before you feed it to your script.
> The trick is to multiply all pixels at the edges by 0.5. This can be done with a white mask which has gray pixels at the edge.
> 

Thank you for your reply.

> ffmpeg -f lavfi -i color=color=white:size=1920x1080 -lavfi drawbox=color=gray:t=1 -frames 1 -y mask.png

This works.

> 
> ffmpeg -f lavfi -i testsrc2=size=1920x1080 -i mask.png -lavfi multiply=offset=0 -frames 1 -y test.png

But ffmpeg says multiply filter doesn’t exist. 

I tried that:
ffmpeg -f lavfi -i testsrc2=size=1920x1080 -i mask.png -lavfi blend=all_mode=multiply -frames 1 -y test.png

output gets green.


ffmpeg -f lavfi -i testsrc=size=1920x1080 -i mask.png -lavfi blend=all_mode=multiply -frames 1 -y test.png
Works!

If I take a video, the video output gets green.

> 
> Then use test.png as input for your script.
> 
> Michael
> 
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