x265代码阅读：码率控制（二）

头文件x265.h中的码率控制参数：

    struct    {        /* Explicit mode of rate-control, necessary for API users. It must         * be one of the X265_RC_METHODS enum values. */        int       rateControlMode;        /* Base QP to use for Constant QP rate control. Adaptive QP may alter         * the QP used for each block. If a QP is specified on the command line         * CQP rate control is implied. Default: 32 */        int       qp;        /* target bitrate for Average BitRate (ABR) rate control. If a non- zero         * bitrate is specified on the command line, ABR is implied. Default 0 */        int       bitrate;        /* qComp sets the quantizer curve compression factor. It weights the frame         * quantizer based on the complexity of residual (measured by lookahead).         * Default value is 0.6. Increasing it to 1 will effectively generate CQP */        double    qCompress;        /* QP offset between I/P and P/B frames. Default ipfactor: 1.4         * Default pbFactor: 1.3 */        double    ipFactor;        double    pbFactor;        /* Max QP difference between frames. Default: 4 */        int       qpStep;        /* Ratefactor constant: targets a certain constant "quality".         * Acceptable values between 0 and 51. Default value: 28 */        double    rfConstant;        /* Enable adaptive quantization. This mode distributes available bits between all         * CTUs of a frame, assigning more bits to low complexity areas. Turning         * this ON will usually affect PSNR negatively, however SSIM and visual quality         * generally improves. Default: X265_AQ_VARIANCE */        int       aqMode;        /* Sets the strength of AQ bias towards low detail CTUs. Valid only if         * AQ is enabled. Default value: 1.0. Acceptable values between 0.0 and 3.0 */        double    aqStrength;        /* Sets the maximum rate the VBV buffer should be assumed to refill at         * Default is zero */        int       vbvMaxBitrate;        /* Sets the size of the VBV buffer in kilobits. Default is zero */        int       vbvBufferSize;        /* Sets how full the VBV buffer must be before playback starts. If it is less than         * 1, then the initial fill is vbv-init * vbvBufferSize. Otherwise, it is         * interpreted as the initial fill in kbits. Default is 0.9 */        double    vbvBufferInit;        /* Enable CUTree ratecontrol. This keeps track of the CUs that propagate temporally         * across frames and assigns more bits to these CUs. Improves encode efficiency.         * Default: enabled */        int       cuTree;        /* In CRF mode, maximum CRF as caused by VBV. 0 implies no limit */        double    rfConstantMax;        /* In CRF mode, minimum CRF as caused by VBV */        double    rfConstantMin;        /* Multi-pass encoding */        /* Enable writing the stats in a multipass encode to the stat output file */        int       bStatWrite;        /* Enable loading data from the stat input file in a multi pass encode */        int       bStatRead;        /* Filename of the 2pass output/input stats file, if unspecified the         * encoder will default to using x265_2pass.log */        char*     statFileName;        /* temporally blur quants */        double    qblur;        /* temporally blur complexity */        double    complexityBlur;        /* Enable slow and a more detailed first pass encode in multi pass rate control */        int       bEnableSlowFirstPass;        /* ratecontrol overrides */        int        zoneCount;        x265_zone* zones;        /* specify a text file which contains MAX_MAX_QP + 1 floating point         * values to be copied into x265_lambda_tab and a second set of         * MAX_MAX_QP + 1 floating point values for x265_lambda2_tab. All values         * are separated by comma, space or newline. Text after a hash (#) is         * ignored. The lambda tables are process-global, so these new lambda         * values will affect all encoders in the same process */        const char* lambdaFileName;        /* Enable stricter conditions to check bitrate deviations in CBR mode. May compromise            quality to maintain bitrate adherence */        int bStrictCbr;    } rc;

成员变量aqMode和aqStrength是一起使用的，用于assign more bits to low complexity CTUs，这种应该属于空域的RDO，而complexityBlur、blurredComplexity、cuTree均属于时域的RDO。
aqMode和aqStrength的作用类似于HM中的CU级多QP优化，但不需要遍历多个QP。cuTree在HM编码器中没看到类似的技术。