$ cat mylist.txt
file '/path/to/file1'
file '/path/to/file2'
file '/path/to/file3'
 
$ ffmpeg -f concat -i mylist.txt -c copy output

ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg
ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg
cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg
ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi