FFMPEG - Add intro and outro to a video
It's possible. Use

ffmpeg -loop 1 -i image.png -f lavfi -t 5 -i anullsrc -i video.mp4 -i music.wav \
-filter_complex "[0]trim=duration=5,fps=N[pre];[3]showwaves=WxH:r=N[b]; \
                 [b][0]overlay=shortest=1[post]; \
                 [pre][1:a][2:v][2:a][post][3]concat=n=3:v=1:a=1[v][a]" \
-map [v] -map [a] out.mp4


The image and video have to be of the same dimensions. If not, you should scale one of them, likely the image.

The fps filter should be set to the framerate of the video.

The showwaves is a kludge. Since the looped image stream does not terminate, I generate a video stream using showwaves from the audio, which will be of the same length as the WAV. WxH should be the same as the video, and r the same as the video's framerate.

Then the image is overlaid on top the filter is set to terminate when the waves video ends.

Finally, the concat filter assembles the full video.