Replacing audio track in MP4 with FFMPEG

[nicksteel]

Wish to replace the audio track on a MP4 screensaver.
The tracks are different duration, so with final duration being the shorter of the two.
Get invalid file index 1

Also, is there an easier way to do this?

[poisondeathray]

Your command only has 1 input (-i), but you reference 2 inputs with -map 0:0 and -map 1:0

You need to specify the 2nd input after the mp4, something like -i input.mp3 (or whatever audio) , and if it's a compatible audio type in mp4, you can use -acodec copy

[nicksteel]

Thanks! It has been years since I used ffmpeg, so silly mistake and an extra pair of sharp eyes works.