ffmpeg - There is a 4-second sound and the next 8 seconds are lost and repeated

I have a video. but i want that the 4 first seconds have audio and the next 8 second is muted .and repeat it til the end of the video

For example: There is a 30-second video, the first 4 seconds have audio, 4 - 12 seconds is muted, 12-16 have audio, 16-24 is muted, so the video ends

Please help me finish it thank you

Answer

Basic command form is

ffmpeg -i in -af volume=0:enable='gte(mod(t\,12)\,4)' out