How to take multiple inputs with specific trim times to one output, single command ffmpeg
#1 Using concat filter i.e. without textfile

ffmpeg -ss 0 -t 20:00 -i inputA.avi -ss 0 -t 10:00 -i inputB.avi -filter_complex "[0:v][0:a][1:v][1:a]concat=n=2:v=1:a=1" out.mp4


--OR--

#2 Using concat demuxer i.e. with textfile

file inputA-trim.avi
inpoint 0
outpoint 20:00
file inputB-trim.avi
inpoint 0
outpoint 10:00


and then your final command

ffmpeg -f concat -i inputList.txt [rest of command] final.mp4




See https://trac.ffmpeg.org/wiki/Concatenate for details.