[Libav-user] how to change x264 parameters after opening the encoder (avcodec_open2)

[HONGBO LI]

I decode and re encode I frame of a movie  file.

when encode I frame, each I frame need a different qp value. 
How can qp parameter change after
avcodec_open2(CodecCtx, codec, &options) )     ? 

av_dict_set( &options, "qp"   ,  x     , 0 )  is used to set qp.


If x264 parameter can't change after avcodec_open2 function, 
Can I close this encoder and open a new x264 encoder with a new parameter for next I frame?

Thanks