进行编码的时候，加入-crf参数进行码率控制，出现如下问题
Codec AVOption crf (Select the quality for constant quality mode) specified for output file #0 (output.avs) has not been used for any stream. The most likely reason is either wrong type (e.g. a video option with no video streams) or that it is a private option of some encoder which was not actually used for any stream.
是avs2不支持使用-crf进行码率控制吗，那它支持的码率控制方法有哪些