The -itsoffset parameter of FFmpeg is having no effect When rendering my animation video with ffmpeg, I want my video to start with 28-odd seconds of silencebefore the soundtrack begins. 

(Well, I really want it to be 0.28 seconds but making it longer makes debugging easier.)

That's easy enough. According to the manual and SuperUser and others, it is all about adding the -itsoffset parameter before the audio input you wish to delay.

Here's my command line:

ffmpeg -y -itsoffset 28.84 -i soundtrack.wav -framerate 30 -i %d.png -r 30 -vcodec mpeg4 generated.mp4


It generates the video, but the soundtrack starts immediately.

I am stll new to FFmpeg, so I assume I am missing something obvious.
You can use the adelay filter for MP4.

ffmpeg -y -i soundtrack.wav -framerate 30 -i %d.png -af "adelay=28840|28840" -r 30 -vcodec mpeg4 generated.mp4