I'm successfully streaming silent video with music added from my Raspberry Pi (Raspbian) to YouTube via ffmpeg, with the help of this GitHub gist and this post:
raspivid -o - -t 0 -vf -hf -w 1280 -h 720 -fps 25 -b 4000000 | \
ffmpeg -i music.wav \
-f h264 -i - -vcodec copy -acodec aac -ab 128k -g 50 -strict experimental \
-f flv rtmp://a.rtmp.youtube.com/live2/STREAMKEY
The last step of my project to add a transparent, full width/height png overlay to the video (1280x720 size in my case). I've seen a few related answers such as this one and this one.
With the added complexity of piping in a camera feed, mixing in an audio source and outputting to a video stream, I haven't succeeded in adding the image overlay. Where/how would I add a transparent image overlay in the example above?