.. _video_decoding:

视频解码
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.. _functional_constraints_of_video_decoding:

功能约束
"""""""""""""""""""""""""""""""""""""""""""""""""""""

视频解码功能的功能约束参见下表。

.. _table_11_video_decoding_constraints:

表 视频解码功能约束
"""""""""""""""""""""""""""""""""""""""""""""""""""""

+----------+-----------+------------------------------------------------------------+
| 约束项   | 属性      | 参数                                                       |
+==========+===========+============================================================+
| 输入     | 分辨率    | - 最大：4096×4096                                          |
|          |           | - 最小：16×16                                              |
|          |           | - 宽高2对齐                                                |
|          +-----------+------------------------------------------------------------+
|          | 格式      | - H.264 Baseline/Main/High/High 10 Profile                 |
|          |           | - H.265 Main/Main 10 Profile                               |
|          +-----------+------------------------------------------------------------+
|          | 缩放      | 支持2倍缩小和4倍缩小，缩小后的宽高需要2对齐                |
|          +-----------+------------------------------------------------------------+
|          | 输入内存  | 输入内存是Client侧内存                                     |
|          +-----------+------------------------------------------------------------+
|          | 输入方式  | - 只支持按帧输入的码流进行视频解码                         |
|          |           | - 只支持逐行扫描方式编码出来的码流解码                     |
+----------+-----------+------------------------------------------------------------+
| 输出     | 输出格式  | - YUV420SP NV12                                            |
|          |           | - YUV420SP NV21                                            |
|          |           | - YUV420P YU12                                             |
|          |           | - NV12 10bit                                               |
|          +-----------+------------------------------------------------------------+
|          | 分辨率    | - 最大：4096×4096                                          |
|          |           | - 最小：16×16                                              |
|          |           | - 宽高2对齐                                                |
|          +-----------+------------------------------------------------------------+
|          | 输出内存  | 只能调用lynMalloc和lynFree进行视频解码输出的内存申请和释放 |
+----------+-----------+------------------------------------------------------------+

.. _video_decoding_process:

视频解码
"""""""""""""""""""""""""""""""""""""""""""""""""""""

用户可以从LynSDK提供的示例代码中查看完整样例，在示例代码中，调用各接口后都添加了异常判断和处理，以下是关键步骤代码示例，仅供参考，不可以直接拷贝编译。

.. code-block:: c++

    // 预定义解码器输出buffer管理类
    class DecRecvBufManager {
    public:
        int Init(int size, int num) {
            void *newBuf;
            int ret;
            for (int i = 0; i < num; i++) {
                ret = lynMalloc(&newBuf, size);
                m_bufAll.push_back(newBuf);
                m_freeBuf.push(newBuf);
            }
        }
        void *GetNewBuf(uint32_t timeout = 300 * g_channelNum) {
            std::unique_lock<std::mutex> lock(m_queueMux);
            if (m_cvOutbufNum.wait_for(lock, std::chrono::seconds(timeout), 
            [this]{return this->m_freeBuf.size() > 0;}) != true) {
                return nullptr;
            }
            void *buf = m_freeBuf.front();
            m_freeBuf.pop();
            return buf;
        }
        void FreeBuf(void *buf) {
            std::unique_lock<std::mutex> lock(m_queueMux);
            m_freeBuf.push(buf);
            lock.unlock();
            m_cvOutbufNum.notify_one();
        }
        void Destory() {
            for (auto it : m_bufAll) {
                lynFree(it);
            }
            m_bufAll.clear();
        }
        ~DecRecvBufManager() {
            Destory();
        }
    private:
        std::queue<void *> m_freeBuf;
        std::vector<void *> m_bufAll;
        std::mutex m_queueMux;
        std::condition_variable m_cvOutbufNum;
    };

    // 解码器输出信息
    struct VdecBufInfo {
        int id;
        uint8_t *data;
        uint32_t size;
        uint32_t num;
        DecRecvBufManager *manager;
    };

    // 解码器工作线程函数
    int DecodeUrl(const char *url)
    {
        lynError_t ret = 0;
        //runtime资源申请
        lynContext_t context = nullptr;
        ret = lynCreateContext(&context, 0);
        //解封装初始化
        lynDemuxHandle_t demuxHdl;
        ret = lynDemuxOpen(&demuxHdl, url, nullptr);
        lynCodecPara_t codecPara;
        //获取解码参数
        ret = lynDemuxGetCodecPara(demuxHdl, &codecPara);
        int bufSize = codecPara.width * codecPara.height * 3 / 2;

        lynPacket_t pkt;
        int num = 0;
        int totalSize = 0;

        //打开解码器，配置解码参数
        lynVdecAttr_t attr;
        attr.codecId = codecPara.codecId;
        attr.outputFmt = LYN_PIX_FMT_YUV420P;
        lynVdecHandle_t vdecHdl;
        ret = lynVdecOpen(&vdecHdl, &attr);
        int vdecId = ((VdecHandle *)vdecHdl)->id;

        //为视频解码创建发送Stream和接收Stream
        lynStream_t sendStream = nullptr;
        ret = lynCreateStream(&sendStream);
        lynStream_t recvStream = nullptr;
        ret = lynCreateStream(&recvStream);

        //初始化解码器输出buffer
        DecRecvBufManager recvBufManager;
        recvBufManager.Init(bufSize, 5);

        //循环送包过程
        while (1) {
            ret = lynDemuxReadPacket(demuxHdl, &pkt);
            if (ret == EAGAIN) {
                continue;
            } else if (ret != 0) {
                //解码完成，解封装去初始化，并发送eos标识
                lynDemuxClose(demuxHdl);

                /* set eos */
                pkt.eos = true;
                lynVdecSendPacketAsync(sendStream, vdecHdl, &pkt);
                break;
            }

            num++;
            totalSize += pkt.size;

            // 在发送Stream中发送待解码数据
            lynVdecSendPacketAsync(sendStream, vdecHdl, &pkt);
            //同步等待并释放待解码数据内存（可选）
            lynSynchronizeStream(sendStream);
            lynDemuxFreePacket(&pkt);

            //从解码器输出池中获取新的输出buffer并在接收Stream中接收解码之后的图像帧数据
            lynFrame_t frame = {0};
            frame.data = (uint8_t *)recvBufManager.GetNewBuf();
            frame.size = bufSize;
            lynVdecRecvFrameAsync(recvStream, vdecHdl, &frame);

            VdecBufInfo *outBuf = (VdecBufInfo *)malloc(sizeof(VdecBufInfo));
            outBuf->id = vdecId;
            outBuf->data = frame.data;
            outBuf->size = frame.size;
            outBuf->num = num;
            outBuf->manager = &recvBufManager;
            //添加接收Stream异步回调函数，用户可自行选择在回调函数中进行结果保存、内存释放等逻辑
            lynStreamAddAsyncCallback(recvStream, vdec_buffer_callback, outBuf);
        }
        //同步等待直至所有数据解码完成
        lynSynchronizeStream(recvStream);
        //关闭解码器
        lynVdecClose(vdecHdl);
        //runtime资源销毁
        lynDestroyStream(sendStream);
        lynDestroyStream(recvStream);

        lynDestroyContext(context);
        return 0;
    }

    //主函数调用流程
    std::vector<std::thread> decThreads;
    for (int i = 0; i < g_channelNum; i++) {
        decThreads.push_back(std::thread(DecodeUrlThread, g_url.c_str()));
    }
    for (auto &it : decThreads) {
        it.join();
    }