Concate two video file with fade effect with ffmpeg in linux
Your present command specifies stream copy. Since you wish to alter the video frames during the transition, that won't work.
It can be done if you know the duration of the two videos and the duration of fade. Also, for the command below, the resolutions of the two videos should be the same.
ffmpeg -i first.ogg -i second.ogg \
-filter_complex \
&quot;color=black:WxH:d=Video1Length+Video2Length-FadeDuration[base]; \
 [0:v]setpts=PTS-STARTPTS[v0]; \
 [1:v]format=yuva420p,fade=in:st=0:d=FadeDuration:alpha=1, \
      setpts=PTS-STARTPTS+((Video1Length-FadeDuration)/TB)[v1]; \
 [base][v0]overlay[tmp]; \
 [tmp][v1]overlay,format=yuv420p[fv]; \
 [0:a][1:a]acrossfade=d=FadeDuration[fa]&quot; \
-map [fv] -map [fa] \
output.ogg

Replace:
WxH with the resolution of the videos i.e. 640x360
And:
Video1Length, Video2Length, and FadeDuration with their value in seconds.