Can ffmpeg be used to concatenate files?

A while back I asked how to convert mp4 files to mp3 and someone pointed me to ffmpeg. That is a great command and it does a great job.

Now I'd like to know about concatenating files together. Can ffmpeg be used for that? It didn't look like it when I tried to figure it out. Can it, or is there another command for that?

Your question as written doesn't appear to have anything to do with the Ubuntu OS. You'd likely be better served if you asked this question over on the Unix & Linux SE site.

That said, you may want to review the online FFmpeg documentation as it relates to concatenating files, as that appears to directly answer your question. From that site:

If you have media files with exactly the same codec and codec parameters you can concatenate them as described in "Concatenation of files with same codecs". If you have media with different codecs you can concatenate them as described in "Concatenation of files with different codecs" below.

There are ways to combine files in ffmpeg but they are a bit convoluted. So, I use a bash script to make it easier. This is an example of a script that you run with arguments (the names of the files to be combined) and it produces a combined .mp4 file, but you can change the .mp4 extension to something else if you prefer a different type of output file. A temporary file called mylist.txt is created (if a file of that name already exists it will be deleted first) and that is the file that ffmpeg reads to find the list of files to concatenate:

#!/bin/bash

rm -f mylist.txt
# Loop until all input filenames are used up
while [ "$1" != "" ]; do
    echo "file '~/$1'" >> mylist.txt
    # Shift all the input filenames down by one
    shift
done
file="$(date +%Y-%m-%d-%H-%M-%S)"

ffmpeg -f concat -safe 0 -i mylist.txt -c copy "~/combined_$file.mp4"
rm -f mylist.txt

Note that if the files you are combining are too dissimilar you may need to re-encode the video or audio rather than just doing a straight copy as shown here, but that will take much longer and you will probably lose some quality.