Trimming an avi file:
ffmpeg -i Die_Sendung_mit_der_Maus_16.06.19_09-30_ard_30_TVOON_DE.mpg.HQ.avi -vcodec copy -acodec copy -ss 00:06:04 -t 00:29:32 output.avi
ss is the start time and t is the duration (not the end time)
webm to mp3 conversion:
ffmpeg -i La_robe_de_soie.webm -vn -ab 128k -ar 44100 -y "La_robe_de_soie.mp3"
Concatenate two videos:
ffmpeg -f concat -safe 0 -i list.txt -c copy /tmp/output.avi
list.txt:
file 'video1.avi'
file 'video2.avi'