gm1

change audio :

avidemux

cut time :

avidemux

join mp4 :

avconv -i s1.mp4 -c copy -bsf h264_mp4toannexb s1.ts
avconv -i "concat:s1.ts|s2.ts|s3.ts" -c copy -bsf aac_adtstoasc s.mp4
avconv -i s.mp4 -vcodec copy -acodec copy s_fixed.mp4

ffmpeg -i eglise.mp4 -c copy -bsf h264_mp4toannexb q.ts
ffmpeg -i "empty battery 2.mp4" -c copy -bsf h264_mp4toannexb r.ts
ffmpeg -i "concat:q.ts|r.ts" -c copy -bsf aac_adtstoasc qr.mp4

fix time :

ffmpeg -i "final.mp4" -vcodec copy -acodec copy "final fixed.mp4"

move metadata at beginning :

MP4Box -inter 0 final.mp4