overlapping (insufficient)

Watch on youtube.com

doc

https://ffmpeg.org/ffmpeg-filters.html#pad, https://ffmpeg.org/ffmpeg-filters.html#overlay, https://ffmpeg.org/ffmpeg-filters.html#blend, https://ffmpeg.org/ffmpeg-filters.html#amerge, https://ffmpeg.org/ffmpeg-filters.html#pan

In video comparison, overlapping should often be allowed.

overlaying simply

00:00:00

This approach is simple, and although it is functioning, you probably will not be satisfied with this as well. For the overlapping area, we do not want to give top layer priority.

#! /bin/sh
pref="`basename $0 .sh`"
vleft="EuropeanArchive.mp4"
vright="Eduardo.mp4"

#
fac=${1:-80}
cx=$((16 * ${fac}))
cy=$((9 * ${fac}))
ox=$((1920 - 16 * ${fac}))
oy=$((1080 - 9 * ${fac}))
#
ffmpeg -y -i "${vleft}" -i "${vright}" -filter_complex "
[0:v]scale=${cx}:${cy},pad=1920:1080:0:0,setsar=1[v1_1];
[1:v]scale=${cx}:${cy},setsar=1[v2_1];

[v1_1][v2_1]overlay=${ox}:${oy}[v];

[0:a][1:a]amerge=inputs=2,pan=stereo|c0<c0+c1|c1<c2+c3[a]
" -map '[v]' -map '[a]' \
  "${pref}.mp4"

using ‘blend’

00:00:30

This approach is simple, too. And you also will not be satisfied with this. The reason why it gets dark as a whole is because it is an average with the black area (zero). Of course this should not be what you intend, I believe.

#! /bin/sh
pref="`basename $0 .sh`"
vleft="EuropeanArchive.mp4"
vright="Eduardo.mp4"

#
fac=${1:-80}
cx=$((16 * ${fac}))
cy=$((9 * ${fac}))
ox=$((1920 - 16 * ${fac}))
oy=$((1080 - 9 * ${fac}))
#
ffmpeg -y -i "${vleft}" -i "${vright}" -filter_complex "
[0:v]scale=${cx}:${cy},pad=1920:1080:0:0,setsar=1[v1_1];
[1:v]scale=${cx}:${cy},pad=1920:1080:${ox}:${oy},setsar=1[v2_1];

[v1_1][v2_1]blend=average[v];

[0:a][1:a]amerge=inputs=2,pan=stereo|c0<c0+c1|c1<c2+c3[a]
" -map '[v]' -map '[a]' \
  "${pref}.mp4"