How to convert mp3 to mp4 with ffmpeg
Using an image
ffmpeg -loop 1 -i input.jpg -i input.mp3 -vf "scale=1920:1080:force_original_aspect_ratio=decrease,pad=1920:1080:-1:-1:color=black,setsar=1,format=yuv420p" -shortest -fflags +shortest output.mp4
This command uses the scale + pad filters to make image fit into 1920x1080, setsar filter to set a normal Sample Aspect Ratio, then the format filter sets the chroma subsampling to YUV 4:2:0 for playback compatibility.
I also show basic command line tools like cp, mv, ls, and cd.