ffmpeg "concat" question

[wallywalters]

I'm trying to join two video clips, the second with audio but the first without. The command I'm using is

ffmpeg -f concat -i JoinList.txt -c copy JOINED.mp4

and the contents of the JoinList file are

file silent.mp4
file audible.mp4

Unfortunately, this produces a joined file that's silent throughout. Switching the order of the files fixes it, but I need the silent part first. How can I do this (using ffmpeg)?

Thanks!

[poisondeathray]

try adding a silent (blank) audio stream to silent.mp4 before appending

[wallywalters]

I've tried, but the audio stream keeps coming out at a different length than the video. This is my CLI. What am I doing wrong?

ffmpeg -f lavfi -i aevalsrc=0 -i silent_IN.mp4 -shortest -c:v copy -c:a libfdk_aac silent_OUT.mp4

[wallywalters]

Solved it. Making sure the audio frequency of the two clips matched did the trick. What finally worked was

ffmpeg -i silent_IN.mp4 -f lavfi -i aevalsrc=0:s=48000 -c:v copy -shortest silent_OUT.mp4