ffmpeg -i output1.mp4 -i green.mp4 -shortest -filter_complex "[1:v]chromakey=0x00d810:0.1:0.2[ckout];[0:v][ckout]overlay[out]" -map "[out]" output.mp4

output1.mp4为原视频

green.mp4为绿幕视频

chromakey后面0x00d810为颜色16进制，0.01是相似度

overlay为视频左上角