cat VTS_01_*.vob > output.vob
Improved version (this will show a progress bar):
cat VTS_O1_*.VOB | pv | dd of=output.vob
Similar to the 2nd:
pv VTS_01_*.vob > output.vob
Oh and you could also
mv the output.vob to
.mpeg and have it play in VLC or another videoplayer.
ffmpeg -i "concat:VTS_01_1.VOB|VTS_01_2.VOB|VTS_01_3.VOB|VTS_01_4.VOB" -f mpeg -c copy output.mpeg
The methods using
cat do NOT interpret the files and just add them together. 1 typical thing you will notice is a slight hickup when the player goes from 1 to the next VOB. Avidemux (GUI), for instance, will also demux(is that the correct word?) the files so it is a smoother experience.
If you receive the error message
ac3 in MPEG-1 system streams is not widely supported, consider using the vob or the dvd muxer to force a MPEG-2 program stream
then you will need to specify DVD as the output format by adjusting the above ffmpeg command with
... -f dvd ....