ffmpeg libx264 编码 "use an encoding preset (e.g. vpre medium)" 错误解决

最近在做h264编码，一直报这个错误：

broken ffmpeg default settings detected
use an encoding preset (e.g. -vpre medium)
preset usage: -vpre <speed> -vpre <profile>
speed presets are listed in x264 --help
profile is optional; x264 defaults to high

周折了好几天在网上查了大量的资料，结合libx264的源码发现是参数配置的问题，源码在libx264的encoder/encoder.c中：

    /* Detect default ffmpeg settings and terminate with an error. */
    if( b_open )
    {    
        int score = 0; 
        score += h->param.analyse.i_me_range == 0;
        score += h->param.rc.i_qp_step == 3;
        score += h->param.i_keyint_max == 12;
        score += h->param.rc.i_qp_min == 2;
        score += h->param.rc.i_qp_max == 31;
        score += h->param.rc.f_qcompress == 0.5; 
        score += fabs(h->param.rc.f_ip_factor - 1.25) < 0.01;
        score += fabs(h->param.rc.f_pb_factor - 1.25) < 0.01;
        score += h->param.analyse.inter == 0 && h->param.analyse.i_subpel_refine == 8;
        if( score >= 5 )
        {    
            x264_log( h, X264_LOG_ERROR, "broken ffmpeg default settings detected\n" );
            x264_log( h, X264_LOG_ERROR, "use an encoding preset (e.g. -vpre medium)\n" );
            x264_log( h, X264_LOG_ERROR, "preset usage: -vpre <speed> -vpre <profile>\n" );
            x264_log( h, X264_LOG_ERROR, "speed presets are listed in x264 --help\n" );
            x264_log( h, X264_LOG_ERROR, "profile is optional; x264 defaults to high\n" );
            return -1;
        }    
    } 

 解决方法就是在avcodec_open2之前设置AVCodecontex中的几个参数：

 ctx->me_range = 16; 

 ctx->max_qdiff = 4; 

 ctx->qmin = 0; 

 ctx->qmax = 69; 

 ctx->qcompress = 0.6;  

 这几个是libx264默认的参数。

x264编码参数设置可参考http://mewiki.project357.com/wiki/X264_Settings