C++怎么将海康的视频流数据 转码为flv视频流格式

要将海康的视频流数据转码为FLV视频流格式，可以使用FFmpeg库进行实现。以下是一个简单的示例代码，可以将海康、大华等品牌的IPC、NVR等设备的RTSP、RTMP等协议的视频流转换成FLV格式的视频流。

#include <iostream>
#include <sstream>
#include <string>
#include <ctime>
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <unistd.h>
#include <pthread.h>
#include <signal.h>
#include <errno.h>

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

using namespace std;

#define STREAM_DURATION     10.0
#define STREAM_FRAME_RATE   25 /* 25 images/s */
#define STREAM_WIDTH        640
#define STREAM_HEIGHT       480
#define STREAM_PIX_FMT      AV_PIX_FMT_YUV420P /* default pix_fmt */

/* exit a program after printing its usage */
static void usage(const char *progname)
{
    fprintf(stderr, "Usage: %s [options]\n", progname);
    fprintf(stderr, "Options:\n");
    fprintf(stderr, "    -i | --input <filename>      input file name\n");
    fprintf(stderr, "    -o | --output <filename>     output file name\n");
    fprintf(stderr, "    -h | --help                  print this message\n");
    exit(1);
}

static AVFormatContext *ifmt_ctx;
static AVFormatContext *ofmt_ctx;

static int video_stream_index = -1;
static AVStream *video_stream;
static AVCodecContext *video_dec_ctx;
static AVCodecContext *video_enc_ctx;
static AVFrame *frame;
static AVPacket pkt;

static int64_t start_time = 0;
static int64_t last_pts = 0;

static int open_input_file(const char *filename)
{
    int ret;
    AVCodec *dec;

    ifmt_ctx = NULL;
    ret = avformat_open_input(&ifmt_ctx, filename, NULL, NULL);
    if (ret < 0) {
        fprintf(stderr, "Could not open input file '%s'", filename);
        return ret;
    }

    ret = avformat_find_stream_info(ifmt_ctx, NULL);
    if (ret < 0) {
        fprintf(stderr, "Could not find stream information");
        return ret;
    }

    /* select the video stream */
    ret = av_find_best_stream(ifmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, &dec, 0);
    if (ret < 0) {
        fprintf(stderr, "Could not find video stream in the input file");
        return ret;
    }
    video_stream_index = ret;
    video_stream = ifmt_ctx->streams[video_stream_index];

    /* allocate a codec context for the decoder */
    video_dec_ctx = avcodec_alloc_context3(dec);
    if (!video_dec_ctx) {
        fprintf(stderr, "Failed to allocate codec context");
        return AVERROR(EINVAL);
    }

    /* copy codec parameters from input stream to output codec context */
    ret = avcodec_parameters_to_context(video_dec_ctx, video_stream->codecpar);
    if (ret < 0) {
        fprintf(stderr, "Failed to copy codec parameters to decoder context");
        return ret;
    }

    /* init the video decoder */
    ret = avcodec_open2(video_dec_ctx, dec, NULL);
    if (ret < 0) {
        fprintf(stderr, "Failed to open codec");
        return ret;
    }

    /* allocate a frame for the decoded video */
    frame = av_frame_alloc();
    if (!frame) {
        fprintf(stderr, "Failed to allocate frame");
        return AVERROR(ENOMEM);
    }

    return 0;
}

static int open_output_file(const char *filename)
{
    AVCodec *codec;
    int ret;

    ofmt_ctx = NULL;
    avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, filename);
    if (!ofmt_ctx) {
        fprintf(stderr, "Could not create output context");
        return AVERROR_UNKNOWN;
    }

    /* find the encoder */
    codec = avcodec_find_encoder(AV_CODEC_ID_FLV1);
    if (!codec) {
        fprintf(stderr, "Could not find encoder");
        return AVERROR_UNKNOWN;
    }

    /* create a new video stream in the output file */
    video_stream = avformat_new_stream(ofmt_ctx, codec);
    if (!video_stream) {
        fprintf(stderr, "Could not create stream");
        return AVERROR_UNKNOWN;
    }

    video_enc_ctx = avcodec_alloc_context3(codec);
    if (!video_enc_ctx) {
        fprintf(stderr, "Could not allocate codec context");
        return AVERROR(ENOMEM);
    }

    /* set the output codec context parameters */
    video_enc_ctx->bit_rate = 400000;
    video_enc_ctx->width = STREAM_WIDTH;
    video_enc_ctx->height = STREAM_HEIGHT;
    video_enc_ctx->time_base = (AVRational){1, STREAM_FRAME_RATE};
    video_enc_ctx->gop_size = 10;
    video_enc_ctx->max_b_frames = 1;
    video_enc_ctx->pix_fmt = STREAM_PIX_FMT;
    if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
        video_enc_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;

    /* init the video encoder */
    ret = avcodec_open2(video_enc_ctx, codec, NULL);
    if (ret < 0) {
        fprintf(stderr, "Failed to open encoder");
        return ret;
    }

    /* copy the codec context parameters to the output stream */
    ret = avcodec_parameters_from_context(video_stream->codecpar, video_enc_ctx);
    if (ret < 0) {
        fprintf(stderr, "Failed to copy codec parameters to output stream");
        return ret;
    }
    video_stream->time_base = video_enc_ctx->time_base;

    /* set the output file format */
    ret = avio_open(&ofmt_ctx->pb, filename, AVIO_FLAG_WRITE);
    if (ret < 0) {
        fprintf(stderr, "Could not open output file '%s'", filename);
        return ret;
    }
    ret = avformat_write_header(ofmt_ctx, NULL);
    if (ret < 0) {
        fprintf(stderr, "Failed to write output file header");
        return ret;
    }

    return 0;
}

static int write_frame(AVFormatContext *fmt_ctx, const AVRational *time_base, AVStream *stream, AVPacket *pkt)
{
    pkt->stream_index = stream->index;
    av_packet_rescale_ts(pkt, *time_base, stream->time_base);
    return av_interleaved_write_frame(fmt_ctx, pkt);
}

static int flush_encoder(AVFormatContext *fmt_ctx, unsigned int stream_index)
{
    int ret;
    int got_frame;
    AVPacket enc_pkt;
    if (!(fmt_ctx->streams[stream_index]->codecpar->codec->capabilities &
          AV_CODEC_CAP_DELAY))
        return 0;
    while (1) {
        enc_pkt.data = NULL;
        enc_pkt.size = 0;
        av_init_packet(&enc_pkt);
        ret = avcodec_send_frame(fmt_ctx->streams[stream_index]->codec, NULL);
        if (ret < 0)
            break;
        while (1) {
            ret = avcodec_receive_packet(fmt_ctx->streams[stream_index]->codec, &enc_pkt);
            if (ret < 0)
                break;
            got_frame = 1;
            ret = write_frame(fmt_ctx, &fmt_ctx->streams[stream_index]->time_base, fmt_ctx->streams[stream_index], &enc_pkt);
            if (ret < 0)
                break;
        }
        if (ret == AVERROR_EOF)
            return 0;
    }
    return ret;
}

int main(int argc, char **argv)
{
    int ret;
    AVPacket packet = {0};
    int64_t end_pts;
    int64_t pts = 0;
    int64_t duration;
    int64_t cur_time;
    int64_t last_time;
    int video_frame_count = 0;

    const char *input_filename = NULL;
    const char *output_filename = NULL;

    /* parse the command-line options */
    for (int i = 1; i < argc; i++) {
        if (!strcmp(argv[i], "-h") || !strcmp(argv[i], "--help")) {
            usage(argv[0]);
        }
        else if (!strcmp(argv[i], "-i") || !strcmp(argv[i], "--input")) {
            if (i + 1 < argc) {
                input_filename = argv[++i];
            }
            else {
                usage(argv[0]);
            }
        }
        else if (!strcmp(argv[i], "-o") || !strcmp(argv[i], "--output")) {
            if (i + 1 < argc) {
                output_filename = argv[++i];
            }
            else {
                usage(argv[0]);
            }
        }
        else {
            usage(argv[0]);
        }
    }

    /* check that input and output filenames have been provided */
    if (!input_filename || !output_filename) {
        usage(argv[0]);
    }

    /* register all codecs and formats */
    av_register_all();

    /* open the input file */
    ret = open_input_file(input_filename);
    if (ret < 0) {
        fprintf(stderr, "Failed to open input file '%s'", input_filename);
        exit(1);
    }

    /* open the output file */
    ret = open_output_file(output_filename);
    if (ret < 0) {
        fprintf(stderr, "Failed to open output file '%s'", output_filename);
        exit(1);
    }

    /* set the start time */
    start_time = av_gettime();

    /* encode video frames */
    while (1) {
        /* get the next video frame */
        ret = av_read_frame(ifmt_ctx, &packet);
        if (ret < 0) {
            /* end of stream */
            break;
        }

        /* check if this packet belongs to the video stream */
        if (packet.stream_index == video_stream_index) {
            /* decode the video frame */
            ret = avcodec_send_packet(video_dec_ctx, &packet);
            if (ret < 0) {
                fprintf(stderr, "Error submitting a packet for decoding");
                break;
            }

            while (ret >= 0) {
                ret = avcodec_receive_frame(video_dec_ctx, frame);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
                    break;
                else if (ret < 0) {
                    fprintf(stderr, "Error during decoding");
                    exit(1);
                }

                /* encode the video frame */
                frame->pts = pts++;
                av_init_packet(&pkt);
                pkt.data = NULL;
                pkt.size = 0;
                ret = avcodec_send_frame(video_enc_ctx, frame);
                if (ret < 0) {
                    fprintf(stderr, "Error submitting a frame for encoding");
                    break;
                }

                while (ret >= 0) {
                    ret = avcodec_receive_packet(video_enc_ctx, &pkt);
                    if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
                        break;
                    else if (ret < 0) {
                        fprintf(stderr, "Error during encoding");
                        exit(1);
                    }

                    /* write the encoded video frame to the output file */
                    duration = pkt.duration;
                    cur_time = av_gettime() - start_time;
                    if (last_pts) {
                        duration = pkt.pts - last_pts;
                    }
                    else {
                        duration = 0;
                    }
                    last_time = duration * av_q2d(video_stream->time_base) * 1000;
                    if (cur_time < last_time) {
                        usleep((last_time - cur_time) * 1000);
                    }
                    ret = write_frame(ofmt_ctx, &video_stream->time_base, video_stream, &pkt);
                    if (ret < 0) {
                        fprintf(stderr, "Error writing video frame");
                        break;
                    }
                    av_packet_unref(&pkt);

                    last_pts = pkt.pts;
                    end_pts = pkt.pts + pkt.duration;
                    video_frame_count++;
                }
            }
        }
        av_packet_unref(&packet);
    }

    /* flush the video encoder */
    ret = flush_encoder(ofmt_ctx, video_stream_index);
    if (ret < 0) {
        fprintf(stderr, "Error flushing video encoder");
        exit(1);
    }

    /* write the trailer */
    av_write_trailer(ofmt_ctx);

    /* print the summary */
    printf("Video frames: %d\n", video_frame_count);

    /* free the resources */
    avcodec_free_context(&video_dec_ctx);
    avcodec_free_context(&video_enc_ctx);
    avformat_close_input(&ifmt_ctx);
    avformat_free_context(ofmt_ctx);
    av_frame_free(&frame);

    return 0;
}

注：上述代码仅为示例代码，需要根据具体情况进行修改，比如调整视频尺寸等参数。