x265-1.7版本-encoder/dpb.cpp注释

注：问号以及未注释部分 会在x265-1.8版本内更新

/*****************************************************************************
 * Copyright (C) 2013 x265 project
 *
 * Authors: Steve Borho <steve@borho.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02111, USA.
 *
 * This program is also available under a commercial proprietary license.
 * For more information, contact us at license @ x265.com.
 *****************************************************************************/

#include "common.h"
#include "frame.h"
#include "framedata.h"
#include "picyuv.h"
#include "slice.h"

#include "dpb.h"

using namespace x265;

DPB::~DPB()
{
    while (!m_freeList.empty())
    {
        Frame* curFrame = m_freeList.popFront();
        curFrame->destroy();
        delete curFrame;
    }

    while (!m_picList.empty())
    {
        Frame* curFrame = m_picList.popFront();
        curFrame->destroy();
        delete curFrame;
    }

    while (m_picSymFreeList)
    {
        FrameData* next = m_picSymFreeList->m_freeListNext;
        m_picSymFreeList->destroy();

        m_picSymFreeList->m_reconPic->destroy();
        delete m_picSymFreeList->m_reconPic;

        delete m_picSymFreeList;
        m_picSymFreeList = next;
    }
}

// move unreferenced pictures from picList to freeList for recycle
void DPB::recycleUnreferenced()
{
    Frame *iterFrame = m_picList.first();

    while (iterFrame)
    {
        Frame *curFrame = iterFrame;
        iterFrame = iterFrame->m_next;
        if (!curFrame->m_encData->m_bHasReferences && !curFrame->m_countRefEncoders)
        {
            curFrame->m_reconRowCount.set(0);
            curFrame->m_bChromaExtended = false;

            // iterator is invalidated by remove, restart scan
            m_picList.remove(*curFrame);
            iterFrame = m_picList.first();

            m_freeList.pushBack(*curFrame);
            curFrame->m_encData->m_freeListNext = m_picSymFreeList;
            m_picSymFreeList = curFrame->m_encData;
            curFrame->m_encData = NULL;
            curFrame->m_reconPic = NULL;
        }
    }
}
/** 函数功能       ： 设置NAL单元类型，将待编码帧加入DPB列表，获取slice参考帧列表等slice参量，将该帧的参考帧的被参考次数加一
/*  调用范围       ： 只在Encoder::encode函数中被调用
* \参数 newFrame   ： 待编码帧
*   返回值         ： null
**/
void DPB::prepareEncode(Frame *newFrame)
{
    Slice* slice = newFrame->m_encData->m_slice;//获取当前frame的slice
    slice->m_poc = newFrame->m_poc;//设置当前slice的poc

    int pocCurr = slice->m_poc;//当前poc
    int type = newFrame->m_lowres.sliceType;//获取当前帧类型
    bool bIsKeyFrame = newFrame->m_lowres.bKeyframe;//当前是否为关键帧

    slice->m_nalUnitType = getNalUnitType(pocCurr, bIsKeyFrame);//返回前置图像NAL类型，后置图像NAL类型，关键帧NAL类型（并不是最终类型）
    if (slice->m_nalUnitType == NAL_UNIT_CODED_SLICE_IDR_W_RADL)//如果是IDR类型，设置最近的一个关键帧位置 （只在openGOP关闭下）
        m_lastIDR = pocCurr;
    slice->m_lastIDR = m_lastIDR;//设置关键帧位置（所有poc=0都是此类型，所以可以不再if里面）
    slice->m_sliceType = IS_X265_TYPE_B(type) ? B_SLICE : (type == X265_TYPE_P) ? P_SLICE : I_SLICE;//确定slice类型

    if (type == X265_TYPE_B)//如果是不可参考B帧
    {
        newFrame->m_encData->m_bHasReferences = false;//没有帧参考它 设为false

        // Adjust NAL type for unreferenced B frames (change from _R "referenced"
        // to _N "non-referenced" NAL unit type)
        switch (slice->m_nalUnitType)
        {
        case NAL_UNIT_CODED_SLICE_TRAIL_R: //被参考的后置图像，且非TSA、非STSA的视频片段
            slice->m_nalUnitType = m_bTemporalSublayer ? NAL_UNIT_CODED_SLICE_TSA_N : NAL_UNIT_CODED_SLICE_TRAIL_N;//设置未被参考
            break;
        case NAL_UNIT_CODED_SLICE_RADL_R://RADL 前置图像(不依赖IRAP前的帧) 被参考的前置图像  只在openGOP关闭才会有此类型
            slice->m_nalUnitType = NAL_UNIT_CODED_SLICE_RADL_N;//设置未被参考
            break;
        case NAL_UNIT_CODED_SLICE_RASL_R://RASL 前置图像(依赖IRAP前的帧)   被参考的前置图像  只在openGOP打开才会有此类型
            slice->m_nalUnitType = NAL_UNIT_CODED_SLICE_RASL_N;//设置未被参考
            break;
        default:
            break;
        }
    }
    else
    {
        /* m_bHasReferences starts out as true for non-B pictures, and is set to false
         * once no more pictures reference it */
        newFrame->m_encData->m_bHasReferences = true;//可能有帧参考它设为true
    }

    m_picList.pushFront(*newFrame);//将帧加入到队列首位置

    // Do decoding refresh marking if any
    decodingRefreshMarking(pocCurr, slice->m_nalUnitType);//遇到关键帧，设置关键帧前的被参考状态（一般置为false）

    computeRPS(pocCurr, slice->isIRAP(), &slice->m_rps, slice->m_sps->maxDecPicBuffering);//slice中rps获取参考帧列表

    // Mark pictures in m_piclist as unreferenced if they are not included in RPS
    applyReferencePictureSet(&slice->m_rps, pocCurr);//将DPB m_picList列表中在不属于当前帧的参考帧列表的参考状态置为false

    slice->m_numRefIdx[0] = X265_MIN(m_maxRefL0, slice->m_rps.numberOfNegativePictures); // 获取L0最大帧数 Ensuring L0 contains just the -ve POC
    slice->m_numRefIdx[1] = X265_MIN(m_maxRefL1, slice->m_rps.numberOfPositivePictures); // 获取L1最大帧数
    slice->setRefPicList(m_picList);//获取参考帧List 以及 POC

    X265_CHECK(slice->m_sliceType != B_SLICE || slice->m_numRefIdx[1], "B slice without L1 references (non-fatal)\n");

    if (slice->m_sliceType == B_SLICE)
    {
        /* TODO: the lookahead should be able to tell which reference picture
         * had the least motion residual.  We should be able to use that here to
         * select a colocation reference list and index */
        slice->m_colFromL0Flag = false;//时域MV预测的collocated块标记位
        slice->m_colRefIdx = 0;//时域MV预测的collocated图像的参考索引号
        slice->m_bCheckLDC = false;//暂时没发现其用途
    }
    else
    {
        slice->m_bCheckLDC = true;//暂时没发现其用途
        slice->m_colFromL0Flag = true;//时域MV预测的collocated块标记位
        slice->m_colRefIdx = 0;//时域MV预测的collocated图像的参考索引号
    }
    slice->m_sLFaseFlag = (SLFASE_CONSTANT & (1 << (pocCurr % 31))) > 0;//计算m_sLFaseFlag值

    /* Increment reference count of all motion-referenced frames to prevent them
     * from being recycled. These counts are decremented at the end of
     * compressFrame() */
    //将当前帧的参考帧的参考次数都自加一
    int numPredDir = slice->isInterP() ? 1 : slice->isInterB() ? 2 : 0;//获取当前有几个list
    for (int l = 0; l < numPredDir; l++)
    {
        for (int ref = 0; ref < slice->m_numRefIdx[l]; ref++)
        {
            Frame *refpic = slice->m_refPicList[l][ref];
            ATOMIC_INC(&refpic->m_countRefEncoders);//原子锁，自加一
        }
    }
}
/** 函数功能           ： slice中rps获取参考帧列表
/*  调用范围           ： 只在DPB::prepareEncode函数中被调用
* \参数 curPoc         ： 当前帧的POC
* \参数 isRAP          ： 是否关键帧
* \参数 rps            ： slice中的rps &slice->m_rps
* \参数 maxDecPicBuffer： 解码需要的最大buffer大小
*   返回值             ： null
**/
void DPB::computeRPS(int curPoc, bool isRAP, RPS * rps, unsigned int maxDecPicBuffer)
{
    unsigned int poci = 0, numNeg = 0, numPos = 0;//poci：计数参考帧, numNeg：计数前向参考帧, numPos：计数后向参考帧;

    Frame* iterPic = m_picList.first();

    while (iterPic && (poci < maxDecPicBuffer - 1))//在最大buffer内寻求参考帧
    {
        if ((iterPic->m_poc != curPoc) && iterPic->m_encData->m_bHasReferences)//不是当前帧且是可被参考的帧
        {
            rps->poc[poci] = iterPic->m_poc;//获取参考帧poc
            rps->deltaPOC[poci] = rps->poc[poci] - curPoc;//获取参考帧间的poc差值
            (rps->deltaPOC[poci] < 0) ? numNeg++ : numPos++;//记录前后参考帧个数
            rps->bUsed[poci] = !isRAP;//记录是否应用
            poci++;//计数
        }
        iterPic = iterPic->m_next;
    }

    rps->numberOfPictures = poci;//获取参考帧数目
    rps->numberOfPositivePictures = numPos;//后向帧个数
    rps->numberOfNegativePictures = numNeg;//前向帧个数

    rps->sortDeltaPOC();//将RPS列表中的deltaPOC和bused 按照 远 近 （当前帧） 近 远的次序排序
}

/* Marking reference pictures when an IDR/CRA is encountered. */
/** 函数功能       ： 遇到关键帧，设置关键帧前的被参考状态（一般置为false）
/*  调用范围       ： 只在DPB::prepareEncode函数中被调用
* \参数 pocCurr    ： 当前帧的POC
* \参数 nalUnitType： 帧类型
*   返回值         ： null
**/
void DPB::decodingRefreshMarking(int pocCurr, NalUnitType nalUnitType)
{
    if (nalUnitType == NAL_UNIT_CODED_SLICE_IDR_W_RADL)//如果当前是IDR 不是CRA
    {
        /* If the nal_unit_type is IDR, all pictures in the reference picture
         * list are marked as "unused for reference" */
        Frame* iterFrame = m_picList.first();//获取队列第一帧
        while (iterFrame)
        {
            if (iterFrame->m_poc != pocCurr)
                iterFrame->m_encData->m_bHasReferences = false;  //将buffer里面的帧都置为没有帧参考 因为当前IDR帧之后的帧一定不会继续参考前面这些帧了
            iterFrame = iterFrame->m_next;
        }
    }
    else // CRA or No DR
    {
        if (m_bRefreshPending && pocCurr > m_pocCRA)//当前帧已经在CRA帧后面 并且 m_bRefreshPending为true  将CRA前的帧的参考置为false
        {
            /* If the bRefreshPending flag is true (a deferred decoding refresh
             * is pending) and the current temporal reference is greater than
             * the temporal reference of the latest CRA picture (pocCRA), mark
             * all reference pictures except the latest CRA picture as "unused
             * for reference" and set the bRefreshPending flag to false */
            Frame* iterFrame = m_picList.first();
            while (iterFrame)
            {
                if (iterFrame->m_poc != pocCurr && iterFrame->m_poc != m_pocCRA)
                    iterFrame->m_encData->m_bHasReferences = false;  //在CRA帧之后，前置帧将不被参考
                iterFrame = iterFrame->m_next;
            }

            m_bRefreshPending = false;//前置状态置为false
        }
        if (nalUnitType == NAL_UNIT_CODED_SLICE_CRA)//CRA 关键帧 在openGOP时使用
        {
            /* If the nal_unit_type is CRA, set the bRefreshPending flag to true
             * and pocCRA to the temporal reference of the current picture */
            m_bRefreshPending = true; //表示有CRA前置帧
            m_pocCRA = pocCurr;//在openGOP打开下 最近的一个关键帧位置
        }
    }

    /* Note that the current picture is already placed in the reference list and
     * its marking is not changed.  If the current picture has a nal_ref_idc
     * that is not 0, it will remain marked as "used for reference" */
}

/** Function for applying picture marking based on the Reference Picture Set */
/** 函数功能           ： 将DPB m_picList列表中在不属于当前帧的参考帧列表的参考状态置为false
/*  调用范围           ： 只在DPB::prepareEncode函数中被调用
* \参数 rps            ： slice中的rps &slice->m_rps
* \参数 curPoc         ： 当前帧的POC
*   返回值             ： null
**/
void DPB::applyReferencePictureSet(RPS *rps, int curPoc)
{
    // loop through all pictures in the reference picture buffer
    Frame* iterFrame = m_picList.first();
    while (iterFrame)
    {
        if (iterFrame->m_poc != curPoc && iterFrame->m_encData->m_bHasReferences)
        {
            // loop through all pictures in the Reference Picture Set
            // to see if the picture should be kept as reference picture
            bool referenced = false;
            for (int i = 0; i < rps->numberOfPositivePictures + rps->numberOfNegativePictures; i++)//将需要参考的置为ture
            {
                if (iterFrame->m_poc == curPoc + rps->deltaPOC[i])
                {
                    referenced = true;
                    break;
                }
            }
            if (!referenced)
                iterFrame->m_encData->m_bHasReferences = false;//不在上述列表中的 ，其参考位置为false
        }
        iterFrame = iterFrame->m_next;
    }
}

/* deciding the nal_unit_type */
/** 函数功能       ： 返回前置图像NAL类型，后置图像NAL类型，关键帧NAL类型（并不是最终类型）
/*  调用范围       ： 只在DPB::prepareEncode函数中被调用
* \参数 curPOC     ： 当前poc
* \参数 bIsKeyFrame： 是否为IDR帧
*   返回值         ： 返回前置图像NAL类型，后置图像NAL类型，关键帧NAL类型
**/
NalUnitType DPB::getNalUnitType(int curPOC, bool bIsKeyFrame)
{
    if (!curPOC)
        return NAL_UNIT_CODED_SLICE_IDR_W_RADL;//视频序列第一帧， IDR帧，前置帧无参考前面的帧

    if (bIsKeyFrame)//当前为关键帧
        return m_bOpenGOP ? NAL_UNIT_CODED_SLICE_CRA : NAL_UNIT_CODED_SLICE_IDR_W_RADL;//如果打开GOP ， 则当前的关键帧为CRA（其前置图像可以为RASL可以参考前面的帧）

    if (m_pocCRA && curPOC < m_pocCRA)
        // All leading pictures are being marked as TFD pictures here since
        // current encoder uses all reference pictures while encoding leading
        // pictures. An encoder can ensure that a leading picture can be still
        // decodable when random accessing to a CRA/CRANT/BLA/BLANT picture by
        // controlling the reference pictures used for encoding that leading
        // picture. Such a leading picture need not be marked as a TFD picture.
        return NAL_UNIT_CODED_SLICE_RASL_R;//只在打开openGOP情况下进入：如果当前帧号小于最近的关键帧，返回前置图像为RASL_R（被参考的前置图像，并且前置图像也参考其前面的帧）

    if (m_lastIDR && curPOC < m_lastIDR)
        return NAL_UNIT_CODED_SLICE_RADL_R;//只在关闭openGOP情况下进入：如果当前帧号小于最近的关键帧，返回前置图像为RADL_R（被参考的前置图像，并且前置图像不参考其前面的帧）

    return NAL_UNIT_CODED_SLICE_TRAIL_R;//被参考的后置图像，且非TSA、非STSA的视频片段
}