static int estimate_best_b_count(MpegEncContext *s){
    AVCodec *codec= avcodec_find_encoder(s->avctx->codec_id);
    AVCodecContext *c = avcodec_alloc_context3(NULL);
    AVFrame input[FF_MAX_B_FRAMES+2];
    const int scale= s->avctx->brd_scale;
    int i, j, out_size, p_lambda, b_lambda, lambda2;
    int outbuf_size= s->width * s->height; //FIXME
    uint8_t *outbuf= av_malloc(outbuf_size);
    int64_t best_rd= INT64_MAX;
    int best_b_count= -1;

    assert(scale>=0 && scale <=3);

//    emms_c();
    p_lambda= s->last_lambda_for[AV_PICTURE_TYPE_P]; //s->next_picture_ptr->quality;
    b_lambda= s->last_lambda_for[AV_PICTURE_TYPE_B]; //p_lambda *FFABS(s->avctx->b_quant_factor) + s->avctx->b_quant_offset;
    if(!b_lambda) b_lambda= p_lambda; //FIXME we should do this somewhere else
    lambda2= (b_lambda*b_lambda + (1<<FF_LAMBDA_SHIFT)/2 ) >> FF_LAMBDA_SHIFT;

    c->width = s->width >> scale;
    c->height= s->height>> scale;
    c->flags= CODEC_FLAG_QSCALE | CODEC_FLAG_PSNR | CODEC_FLAG_INPUT_PRESERVED /*| CODEC_FLAG_EMU_EDGE*/;
    c->flags|= s->avctx->flags & CODEC_FLAG_QPEL;
    c->mb_decision= s->avctx->mb_decision;
    c->me_cmp= s->avctx->me_cmp;
    c->mb_cmp= s->avctx->mb_cmp;
    c->me_sub_cmp= s->avctx->me_sub_cmp;
    c->pix_fmt = PIX_FMT_YUV420P;
    c->time_base= s->avctx->time_base;
    c->max_b_frames= s->max_b_frames;

    if (avcodec_open2(c, codec, NULL) < 0)
        return -1;

    for(i=0; i<s->max_b_frames+2; i++){
        int ysize= c->width*c->height;
        int csize= (c->width/2)*(c->height/2);
        Picture pre_input, *pre_input_ptr= i ? s->input_picture[i-1] : s->next_picture_ptr;

        avcodec_get_frame_defaults(&input[i]);
        input[i].data[0]= av_malloc(ysize + 2*csize);
        input[i].data[1]= input[i].data[0] + ysize;
        input[i].data[2]= input[i].data[1] + csize;
        input[i].linesize[0]= c->width;
        input[i].linesize[1]=
        input[i].linesize[2]= c->width/2;

        if(pre_input_ptr && (!i || s->input_picture[i-1])) {
            pre_input= *pre_input_ptr;

            if (pre_input.f.type != FF_BUFFER_TYPE_SHARED && i) {
                pre_input.f.data[0] += INPLACE_OFFSET;
                pre_input.f.data[1] += INPLACE_OFFSET;
                pre_input.f.data[2] += INPLACE_OFFSET;
            }

            s->dsp.shrink[scale](input[i].data[0], input[i].linesize[0], pre_input.f.data[0], pre_input.f.linesize[0], c->width,      c->height);
            s->dsp.shrink[scale](input[i].data[1], input[i].linesize[1], pre_input.f.data[1], pre_input.f.linesize[1], c->width >> 1, c->height >> 1);
            s->dsp.shrink[scale](input[i].data[2], input[i].linesize[2], pre_input.f.data[2], pre_input.f.linesize[2], c->width >> 1, c->height >> 1);
        }
    }

    for(j=0; j<s->max_b_frames+1; j++){
        int64_t rd=0;

        if(!s->input_picture[j])
            break;

        c->error[0]= c->error[1]= c->error[2]= 0;

        input[0].pict_type= AV_PICTURE_TYPE_I;
        input[0].quality= 1 * FF_QP2LAMBDA;
        out_size = avcodec_encode_video(c, outbuf, outbuf_size, &input[0]);
//        rd += (out_size * lambda2) >> FF_LAMBDA_SHIFT;

        for(i=0; i<s->max_b_frames+1; i++){
            int is_p= i % (j+1) == j || i==s->max_b_frames;

            input[i+1].pict_type= is_p ? AV_PICTURE_TYPE_P : AV_PICTURE_TYPE_B;
            input[i+1].quality= is_p ? p_lambda : b_lambda;
            out_size = avcodec_encode_video(c, outbuf, outbuf_size, &input[i+1]);
            rd += (out_size * lambda2) >> (FF_LAMBDA_SHIFT - 3);
        }

        /* get the delayed frames */
        while(out_size){
            out_size = avcodec_encode_video(c, outbuf, outbuf_size, NULL);
            rd += (out_size * lambda2) >> (FF_LAMBDA_SHIFT - 3);
        }

        rd += c->error[0] + c->error[1] + c->error[2];

        if(rd < best_rd){
            best_rd= rd;
            best_b_count= j;
        }
    }

    av_freep(&outbuf);
    avcodec_close(c);
    av_freep(&c);

    for(i=0; i<s->max_b_frames+2; i++){
        av_freep(&input[i].data[0]);
    }

    return best_b_count;
}