ffmpeg裁剪视频和openpose生成骨架

1. 剪视频，剪掉25秒之前的视频
   ffmpeg -i Everybody.mp4 -ss 00:00:25 -s 512x288 -c:a copy output.mp4

2. 每帧25个图片输出
   ffmpeg -i output.mp4 -r 25 %5d.png

3. 转换avi到mp4
   ffmpeg -y -loglevel info -i openpose.avi output.mp4

4. openpose生成骨架视频
   cd openpose && ./build/examples/openpose/openpose.bin --video ../video.mp4 --disable_blending true --write_json ./output/ --display 0 --write_video ../openpose.avi