I read your article.
I want to broadcast live on youtube. but youtube say you need a microphone. How do I handle this in raspberry pi4? What should I do?
I solved the problem. select the stream and new run code is here 
raspivid -o - -t 0 -fps 25 -g 50 -rot 180 -n -a 12 -b 6000000 | ffmpeg -re -ar 44100 -ac 2 -acodec pcm_s16le -f s16le -ac 2 -i /dev/zero -f h264 -thread_queue_size 256 -i - -vcodec copy -acodec aac -ab 128k -strict experimental -f flv rtmp://a.rtmp.youtube.com/live2/YOUR_KEY_HERE