The ffmpeg command
ffmpeg -i sample.mp4 -vf "crop=496:279:0:0,setdar=16/9" output.mp4
only keep DAR 16:9 ,height will be converted to 278 ,SAR converted to 278:279.
Setting resolution as 480*270 can keep all arguments unchanged:
ffmpeg -i sample.mp4 -vf "crop=480:270:0:0,setdar=16/9" output.mp4
Now SAR=1:1 ,DAR=16:9.