README.md

#### ffmpeg编译配置
```./configure --enable-debug --extra-cflags=-g --extra-ldflags=-g --disable-optimizations --disable-stripping --enable-cuda --enable-cuvid --enable-nvenc --disable-x86asm --enable-nonfree --enable-libnpp --extra-cflags=-I/usr/local/cuda-11.1/targets/x86_64-linux/include --extra-cflags=-fPIC --extra-ldflags=-L/usr/local/cuda-11.1/targets/x86_64-linux/lib --enable-shared --enable-pic --enable-ffplay --prefix=../bin ```
其中以下是用于调试的，编译release可以去掉：
```--enable-debug --extra-cflags=-g --extra-ldflags=-g --disable-optimizations --disable-stripping```
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