warping on Linux - initial ffmpeg trials without a final solution

I still use the tool made in 2014 to pre-warp fulldome planetarium shows for our planetarium's Blu-ray-player-based playout system. But that tool's main limitation seems to be that it works only on Windows XP. It does not seem to work even on Windows 7 - I tested with RS's laptop.

In the search for alternatives for future-proofing, I had a look at ffmpeg's Remap filter. If a suitable map is made, it should be possible to use this filter to do the warping in a platform independent way.

https://trac.ffmpeg.org/wiki/RemapFilter

https://stackoverflow.com/questions/30832248/is-there-a-way-to-remove-gopro-fisheye-using-ffmpeg

http://paulbourke.net/miscellaneous/ffmpeg/

https://stackoverflow.com/questions/38360837/ffmpeg-remap-filter-not-found 

ffmpeg -i /path/input.mp4 -i front_kodak_sp360_1440_xmap.pgm -i front_kodak_sp360_1440_ymap.pgm -lavfi remap out.mp4

Preliminary test went at around 8 fps, 1 minute video took 4 minutes to encode.

out.mp4 was of a similar format to input file, but not exactly.

mediainfo out.mp4

Testing to see if opengl will be faster, tried with just re-encoding to divx,

ffmpeg -i /path/input.mp4 -c:v libxvid out.mp4

did the 1 minute video in 2 minutes, but quite low quality for the highly changing scenes. That would be 15 fps.

ffmpeg -i /path/input.mp4 -c:v libxvid -qscale:v 100 out.mp4

did not make much of a difference.

Some info about OpenGL filters with ffmpeg

https://nervous.io/ffmpeg/opengl/2017/05/15/ffmpeg-pbo-yuv/

https://nervous.io/ffmpeg/opengl/2017/01/31/ffmpeg-opengl/

In case conversion has a problem,

https://stackoverflow.com/questions/53357909/ffmpeg-remap-with-video

Piping to screen works, albeit not in realtime, 0.25x perhaps.

ffmpeg -i /path/input.mp4 -i front_kodak_sp360_1440_xmap.pgm -i front_kodak_sp360_1440_ymap.pgm -lavfi remap -f matroska - | ffplay -

inspired by

https://superuser.com/questions/322216/how-can-i-pipe-output-of-ffmpeg-to-ffplay

 https://superuser.com/questions/685022/how-can-i-pipe-data-losslessly-to-and-from-ffmpeg

Using rawvideo, (raw RGB is not supported in matroshka, so using NUT), went to 0.68x, but in black and white!

ffmpeg -i /path/input.mp4 -i front_kodak_sp360_1440_xmap.pgm -i front_kodak_sp360_1440_ymap.pgm -lavfi remap -c:v rawvideo -f NUT - | ffplay -

with AVI instead of NUT, colours are mismatched and not antialiased?!

Later, went to try avisynth instead. That is described in another post.