cv::VideoWriter 写入网络流

cv::VideoWriter 可以用来将 OpenCV 的图像序列写入本地视频文件，而不是网络流。如果你要将视频流写入网络流，你需要使用不同的库和方法。例如，FFmpeg 是一个流媒体处理库，它可以将视频数据编码为流，并将其发送到网络。你可以使用 FFmpeg 的 API 在 C++ 中编写代码来实现这一点。以下是一个使用 FFmpeg 将本地视频文件写入网络流的简单示例：

#include <iostream>
#include <sstream>
#include <string>
#include <cstdio>
#include <chrono>
#include <thread>
#include <cstdlib>
#include <cstring>
#include <stdexcept>
#include <sstream>

#include <opencv2/opencv.hpp>

extern "C" {
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavutil/opt.h>
#include <libavutil/imgutils.h>
}

using namespace std;
using namespace cv;

int main(int argc, char** argv)
{
    // Open the local video file
    VideoCapture cap("video.mp4");
    if (!cap.isOpened()) {
        cerr << "Error: Unable to open video file" << endl;
        return -1;
    }

    // Initialize FFmpeg
    av_register_all();
    avcodec_register_all();
    avformat_network_init();

    // Create the output context
    AVFormatContext* outctx = nullptr;
    if (avformat_alloc_output_context2(&outctx, nullptr, "flv", "rtmp://localhost/live") < 0) {
        cerr << "Error: Unable to create output context" << endl;
        return -1;
    }

    // Open the output stream
    AVStream* outstream = avformat_new_stream(outctx, nullptr);
    if (!outstream) {
        cerr << "Error: Unable to create output stream" << endl;
        return -1;
    }

    // Copy the codec parameters from the input stream
    AVCodecParameters* inparams = cap.getBackendType() == VideoCapture::CAP_V4L ? nullptr : avcodec_parameters_alloc();
    if (inparams) {
        inparams->codec_type = AVMEDIA_TYPE_VIDEO;
        inparams->codec_id = AV_CODEC_ID_H264;
        inparams->width = cap.get(CV_CAP_PROP_FRAME_WIDTH);
        inparams->height = cap.get(CV_CAP_PROP_FRAME_HEIGHT);
        inparams->format = AV_PIX_FMT_BGR24;
        inparams->profile = FF_PROFILE_H264_BASELINE;
        inparams->bit_rate = 1000000;
        inparams->bit_rate_tolerance = 10000000;
        inparams->ticks_per_frame = 2;
        inparams->time_base.num = 1;
        inparams->time_base.den = 30;
        avcodec_parameters_to_context(outstream->codecpar, inparams);
    }

    // Open the codec
    AVCodec* codec = avcodec_find_encoder(AV_CODEC_ID_H264);
    if (!codec) {
        cerr << "Error: Unable to find codec" << endl;
        return -1;
    }
    AVCodecContext* codecctx = avcodec_alloc_context3(codec);
    if (!codecctx) {
        cerr << "Error: Unable to create codec context" << endl;
        return -1;
    }
    avcodec_parameters_to_context(codecctx, inparams);
    codecctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
    if (avcodec_open2(codecctx, codec, nullptr) < 0) {
        cerr << "Error: Unable to open codec" << endl;
        return -1;
    }
    avcodec_parameters_from_context(outstream->codecpar, codecctx);

    // Open the output stream
    if (avio_open(&outctx->pb, "rtmp://localhost/live", AVIO_FLAG_WRITE) < 0) {
        cerr << "Error: Unable to open output stream" << endl;
        return -1;
    }
    avformat_write_header(outctx, nullptr);

    // Write the frames to the output stream
    AVPacket pkt;
    av_init_packet(&pkt);
    Mat frame;
    while (cap.read(frame)) {
        // Encode the frame
        AVFrame* avframe = av_frame_alloc();
        avframe->format = codecctx->pix_fmt;
        avframe->width = codecctx->width;
        avframe->height = codecctx->height;
        av_frame_get_buffer(avframe, 32);
        Mat dst(codecctx->height, codecctx->width, CV_8UC3, avframe->data[0], avframe->linesize[0]);
        cvtColor(frame, dst, COLOR_BGR2YUV_I420);
        avframe->pts = cap.get(CV_CAP_PROP_POS_FRAMES);
        avcodec_send_frame(codecctx, avframe);
        while (avcodec_receive_packet(codecctx, &pkt) == 0) {
            pkt.stream_index = outstream->index;
            av_interleaved_write_frame(outctx, &pkt);
            av_packet_unref(&pkt);
        }
        av_frame_free(&avframe);
    }

    // Flush the codec
    avcodec_send_frame(codecctx, nullptr);
    while (avcodec_receive_packet(codecctx, &pkt) == 0) {
        pkt.stream_index = outstream->index;
        av_interleaved_write_frame(outctx, &pkt);
        av_packet_unref(&pkt);
    }

    // Close the output stream
    av_write_trailer(outctx);
    avcodec_close(codecctx);
    avcodec_free_context(&codecctx);
    avformat_close_input(&outctx);
    avformat_free_context(outctx);

    return 0;
}