Intel Media SDK decode_sample剖析(二)——解码数据

接上一篇：https://blog.csdn.net/y601500359/article/details/87260201

接下来开始剖析数据解码函数：RunDecoding

1. 初始化变量，不细说：

2、下面while循环里是为了循环解码数据帧

while (((sts == MFX_ERR_NONE) || (MFX_ERR_MORE_DATA == sts) || (MFX_ERR_MORE_SURFACE == sts)) && (m_nFrames > m_output_count))

{
    .........
}

3、接下来依次剖析while循环里面的代码行：

（1）、在循环时，判断如果一旦输出解码数据（m_error = DeliverOutput(frame);）出错，立即跳出循环

if (MFX_ERR_NONE != m_error) {
            msdk_printf(MSDK_STRING("DeliverOutput return error = %d
"),m_error);
            break;
        }

（2）、在文件播放是，如果数据帧不足一帧，读取下一部分数据：

 if (pBitstream && ((MFX_ERR_MORE_DATA == sts) || (m_bIsCompleteFrame && !pBitstream->DataLength))) {
            CAutoTimer timer_fread(m_tick_fread);
            sts = m_FileReader->ReadNextFrame(pBitstream); // read more data to input bit stream

            if (MFX_ERR_MORE_DATA == sts) {
                sts = MFX_ERR_NONE;
                // Timeout has expired or videowall mode
                m_timer_overall.Sync();
                if ( ((CTimer::ConvertToSeconds(m_tick_overall) < m_nTimeout) && m_nTimeout ) || m_bIsVideoWall)
                {
                    m_FileReader->Reset();
                    m_bResetFileWriter = true;
                    continue;
                }

                // we almost reached end of stream, need to pull buffered data now
                pBitstream = NULL;
            }

（3）、同步数据表面：

if ((MFX_ERR_NONE == sts) || (MFX_ERR_MORE_DATA == sts) || (MFX_ERR_MORE_SURFACE == sts)) {
            SyncFrameSurfaces();
            SyncVppFrameSurfaces();
            if (!m_pCurrentFreeSurface) {
                m_pCurrentFreeSurface = m_FreeSurfacesPool.GetSurface();
            }
            if (!m_pCurrentFreeVppSurface) {
              m_pCurrentFreeVppSurface = m_FreeVppSurfacesPool.GetSurface();
            }
#ifndef __SYNC_WA
            if (!m_pCurrentFreeSurface || !m_pCurrentFreeVppSurface) {
#else
            if (!m_pCurrentFreeSurface || (!m_pCurrentFreeVppSurface && m_bVppIsUsed) || (m_OutputSurfacesPool.GetSurfaceCount() == m_mfxVideoParams.AsyncDepth)) {
#endif
                // we stuck with no free surface available, now we will sync...
                sts = SyncOutputSurface(MSDK_DEC_WAIT_INTERVAL);
                if (MFX_ERR_MORE_DATA == sts) {
                    if ((m_eWorkMode == MODE_PERFORMANCE) || (m_eWorkMode == MODE_FILE_DUMP)) {
                        sts = MFX_ERR_NOT_FOUND;
                    } else if (m_eWorkMode == MODE_RENDERING) {
                        if (m_synced_count != m_output_count) {
                            sts = m_pDeliveredEvent->TimedWait(MSDK_DEC_WAIT_INTERVAL);
                        } else {
                            sts = MFX_ERR_NOT_FOUND;
                        }
                    }
                    if (MFX_ERR_NOT_FOUND == sts) {
                        msdk_printf(MSDK_STRING("fatal: failed to find output surface, that's a bug!
"));
                        break;
                    }
                }
                // note: MFX_WRN_IN_EXECUTION will also be treated as an error at this point
                continue;
            }

            if (!m_pCurrentFreeOutputSurface) 
            {
                m_pCurrentFreeOutputSurface = GetFreeOutputSurface();
            }
            if (!m_pCurrentFreeOutputSurface) 
            {
                sts = MFX_ERR_NOT_FOUND;
                break;
            }
        }

（4）、解码数据：并同步输出表面

 if ((MFX_ERR_NONE == sts) || (MFX_ERR_MORE_DATA == sts) || (MFX_ERR_MORE_SURFACE == sts)) {
            if (m_bIsCompleteFrame) 
            {
                m_pCurrentFreeSurface->submit = m_timer_overall.Sync();
            }
            pOutSurface = NULL;
            do {
#if (MFX_VERSION >= 1025)
                if (pBitstream) {
                    pDecodeErrorReport = (mfxExtDecodeErrorReport *)GetExtBuffer(pBitstream->ExtParam, pBitstream->NumExtParam, MFX_EXTBUFF_DECODE_ERROR_REPORT);
                }
#endif
                sts = m_pmfxDEC->DecodeFrameAsync(pBitstream, &(m_pCurrentFreeSurface->frame), &pOutSurface, &(m_pCurrentFreeOutputSurface->syncp));

#if (MFX_VERSION >= 1025)
                PrintDecodeErrorReport(pDecodeErrorReport);
#endif

                if (pBitstream && MFX_ERR_MORE_DATA == sts && pBitstream->MaxLength == pBitstream->DataLength)
                {
                    mfxStatus stsExt = ExtendMfxBitstream(pBitstream, pBitstream->MaxLength * 2);
                    MSDK_CHECK_STATUS_SAFE(stsExt, "ExtendMfxBitstream failed", MSDK_SAFE_DELETE(pDeliverThread));
                }

                if (MFX_WRN_DEVICE_BUSY == sts) {
                    if (m_bIsCompleteFrame) {
                        //in low latency mode device busy leads to increasing of latency
                        //msdk_printf(MSDK_STRING("Warning : latency increased due to MFX_WRN_DEVICE_BUSY
"));
                    }
                    mfxStatus _sts = SyncOutputSurface(MSDK_DEC_WAIT_INTERVAL);
                    // note: everything except MFX_ERR_NONE are errors at this point
                    if (MFX_ERR_NONE == _sts) {
                        sts = MFX_WRN_DEVICE_BUSY;
                    } else {
                        sts = _sts;
                        if (MFX_ERR_MORE_DATA == sts) {
                            // we can't receive MFX_ERR_MORE_DATA and have no output - that's a bug
                            sts = MFX_WRN_DEVICE_BUSY;//MFX_ERR_NOT_FOUND;
                        }
                    }
                }
            } while (MFX_WRN_DEVICE_BUSY == sts);

            if (sts > MFX_ERR_NONE) {
                // ignoring warnings...
                if (m_pCurrentFreeOutputSurface->syncp) {
                    MSDK_SELF_CHECK(pOutSurface);
                    // output is available
                    sts = MFX_ERR_NONE;
                } else {
                    // output is not available
                    sts = MFX_ERR_MORE_SURFACE;
                }
            } else if ((MFX_ERR_MORE_DATA == sts) && pBitstream) {
                if (m_bIsCompleteFrame && pBitstream->DataLength)
                {
                    // In low_latency mode decoder have to process bitstream completely
                    msdk_printf(MSDK_STRING("error: Incorrect decoder behavior in low latency mode (bitstream length is not equal to 0 after decoding)
"));
                    sts = MFX_ERR_UNDEFINED_BEHAVIOR;
                    continue;
                }
            } else if ((MFX_ERR_MORE_DATA == sts) && !pBitstream) {
                // that's it - we reached end of stream; now we need to render bufferred data...
                do {
                    sts = SyncOutputSurface(MSDK_DEC_WAIT_INTERVAL);
                } while (MFX_ERR_NONE == sts);

                MSDK_IGNORE_MFX_STS(sts, MFX_ERR_MORE_DATA);
                if (sts) MSDK_PRINT_WRN_MSG(sts, "SyncOutputSurface failed")

                while (m_synced_count != m_output_count) {
                    m_pDeliveredEvent->Wait();
                }
                break;
            } else if (MFX_ERR_INCOMPATIBLE_VIDEO_PARAM == sts) {
                bErrIncompatibleVideoParams = true;
                // need to go to the buffering loop prior to reset procedure
                pBitstream = NULL;
                sts = MFX_ERR_NONE;
                continue;
            }
        }

4、SyncOutputSurface函数：

GetSurface：获取链表中的显示表面

SyncOperation：此函数启动执行尚未启动的异步函数，并在指定的异步操作完成之后返回状态码。 如果wait为零，则函数立即返回。注：SyncOperation这个函数要特别注意，因为我在使用时发现部分电脑，在使用该函数时，返回MFX_ERR_UNKNOWN，最后查明原因，操作系统驱动问题，更新到最新后，正常了。

5、DeliverOutput函数：

该函数主要功能是输出，如果是保存文件模式，怎保存yuv数据到文件；如果是渲染模式，则通过D3D渲染。

保存文件：注意是I420格式，Intel media sdk默认解码出来的是NV12格式，WriteNextFrameI420函数里面会进行一个NV12转I420。

        if (m_eWorkMode == MODE_FILE_DUMP) {
            res = m_pGeneralAllocator->Lock(m_pGeneralAllocator->pthis, frame->Data.MemId, &(frame->Data));
            if (MFX_ERR_NONE == res) {
                res = m_bOutI420 ? m_FileWriter.WriteNextFrameI420(frame)
                    : m_FileWriter.WriteNextFrame(frame);
                sts = m_pGeneralAllocator->Unlock(m_pGeneralAllocator->pthis, frame->Data.MemId, &(frame->Data));
            }
            if ((MFX_ERR_NONE == res) && (MFX_ERR_NONE != sts)) {
                res = sts;
            }
        } 

渲染模式：需要注意的是，里面的while循环，这个循环必须要，否则渲染的视频画面会出现时快时慢。

else if (m_eWorkMode == MODE_RENDERING) {
#if D3D_SURFACES_SUPPORT
            res = m_d3dRender.RenderFrame(frame, m_pGeneralAllocator);
#elif LIBVA_SUPPORT
            res = m_hwdev->RenderFrame(frame, m_pGeneralAllocator);
#endif

            while( m_delayTicks && (m_startTick + m_delayTicks > msdk_time_get_tick()) )
            {
                MSDK_SLEEP(0);
            };
            m_startTick=msdk_time_get_tick();
        }

sample就先简要剖析到此。下一篇开始进行实际项目运用。