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

[Michael Koch]

Am 17.07.2022 um 12:09 schrieb 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.

Convert the pixel format of both inputs to RGB24 before using the blend 
filter. Multiply makes no sense in YUV format.

Michael