[FFmpeg-user] Concatenate two mp4 videos - result is not playable

[Maxime Daymard]

Hello,

I'm trying to concat two videos (see link to dropbox) with the command below (concat demuxer), but the result is not playable, and I don't know why.
Basically, when I play the result concatenated video (A+B=C), the playback stops at B. 
I would like to avoid using the concat filter which is slower. If I could only re-encode "video2.mp4" so that the concat works, this would be perfect.
Any help would be really appreciated, thanks in advance !

Command (obviously the concat.txt file must contains the paths to the two input videos) :
ffmpeg -f concat -safe 0 -i concat.txt -c copy -y result.mp4

Both videos can be found on dropbox here (~50M):
https://www.dropbox.com/sh/v99mngn7pfhrfvx/AADKnnJ1trFEF-kPy6p7dssga?dl=0

Thank you again very much in advance !

PS : First time I ask for help here, not sure if it's the right place, but I'm really out of solutions right now :( ..