How to overlay a transparent PNG over video and scale to video size in FFmpeg

Right now I overlay a transparent PNG over a video first converting them both to the same size, but would love to just have it scale within the same command. Here’s the command now:

ffmpeg -y -i video.mp4 -i overlay.png -filter_complex 'overlay[out],amix=inputs=1,pan=stereo:c0=c0:c1=c1' -map '[out]' output.mp4

The best command should also permit a video that does not have an audio track and still overlay the PNG.