Using FFMPEG to add a .mp4 'intro' to .mp4

Hi. I'm trying to use FFMPEG to add a .mp4 clip to the start of a .mp4 video (and failing!).

Please can someone check what I'm doing wrong, because when the output video is created, the video lacks audio! (the actual picture is OK).

Here's whats in my input.txt file (using a concat script):

file 'C:\Vid\UT.mp4'
file 'C:\Vid\1.mp4'


And here's whats in the .BAT file:

ffmpeg -f concat -i input.txt -codec copy output.mp4


Error in cmd shows 'Invalid stream index index 1'.


Many thanks for any help!
Harry