visual studio dav转mp4用ffmpeg的cpp代码

以下是使用FFmpeg进行DAV转MP4的C++代码示例：

#include <iostream>
#include <string>

#define __STDC_CONSTANT_MACROS

#ifdef _WIN32
// Windows
extern "C" {
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libswscale/swscale.h"
#include "libavutil/opt.h"
#include "libavutil/imgutils.h"
#include "libavutil/avutil.h"
}
#else
// Linux...
#ifdef __cplusplus
extern "C" {
#endif
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswscale/swscale.h>
#include <libavutil/opt.h>
#include <libavutil/imgutils.h>
#include <libavutil/avutil.h>
#ifdef __cplusplus
}
#endif
#endif

using namespace std;

int main(int argc, char* argv[]) {
    AVFormatContext *pFormatCtx = NULL;
    AVCodecContext *pCodecCtx = NULL;
    AVCodec *pCodec = NULL;
    AVFrame *pFrame = NULL, *pFrameRGB = NULL;
    AVPacket packet;
    int videoStream = -1;
    int frameFinished;
    int numBytes;
    uint8_t* buffer = NULL;
    int width, height;

    string inputFilePath = "test.dav";
    string outputFilePath = "test.mp4";

    av_register_all();

    if (avformat_open_input(&pFormatCtx, inputFilePath.c_str(), NULL, NULL) != 0) {
        cout << "Couldn't open input file." << endl;
        return -1;
    }

    if (avformat_find_stream_info(pFormatCtx, NULL) < 0) {
        cout << "Couldn't find stream information." << endl;
        return -1;
    }

    av_dump_format(pFormatCtx, 0, inputFilePath.c_str(), 0);

    for (int i = 0; i < pFormatCtx->nb_streams; i++) {
        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
            videoStream = i;
            break;
        }
    }

    if (videoStream == -1) {
        cout << "Couldn't find a video stream." << endl;
        return -1;
    }

    pCodecCtx = pFormatCtx->streams[videoStream]->codec;
    pCodec = avcodec_find_decoder(pCodecCtx->codec_id);

    if (pCodec == NULL) {
        cout << "Codec not found." << endl;
        return -1;
    }

    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0) {
        cout << "Could not open codec." << endl;
        return -1;
    }

    pFrame = av_frame_alloc();
    pFrameRGB = av_frame_alloc();

    if (pFrameRGB == NULL) {
        return -1;
    }

    numBytes = av_image_get_buffer_size(AV_PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height, 1);

    buffer = (uint8_t*)av_malloc(numBytes * sizeof(uint8_t));

    av_image_fill_arrays(pFrameRGB->data, pFrameRGB->linesize, buffer, AV_PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height, 1);

    SwsContext* sws_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_RGB24, SWS_BILINEAR, NULL, NULL, NULL);

    AVFormatContext* pOutFormatCtx = NULL;
    int ret = avformat_alloc_output_context2(&pOutFormatCtx, NULL, NULL, outputFilePath.c_str());

    if (ret < 0) {
        cout << "Could not allocate output format context." << endl;
        return -1;
    }

    AVStream* pOutStream = avformat_new_stream(pOutFormatCtx, NULL);
    if (!pOutStream) {
        cout << "Failed allocating output stream." << endl;
        return -1;
    }

    pOutStream->codecpar->codec_tag = 0;
    avcodec_parameters_from_context(pOutStream->codecpar, pCodecCtx);

    if (!(pOutFormatCtx->oformat->flags & AVFMT_NOFILE)) {
        if (avio_open(&pOutFormatCtx->pb, outputFilePath.c_str(), AVIO_FLAG_WRITE) < 0) {
            cout << "Could not open output file." << endl;
            return -1;
        }
    }

    ret = avformat_write_header(pOutFormatCtx, NULL);
    if (ret < 0) {
        cout << "Error occurred when opening output file." << endl;
        return -1;
    }
    else {
        cout << "Opened output file successfully." << endl;
    }

    int frameCount = 0;

    while (av_read_frame(pFormatCtx, &packet) >= 0) {
        if (packet.stream_index == videoStream) {
            avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
            if (frameFinished) {
                sws_scale(sws_ctx, (uint8_t const * const *)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameRGB->data, pFrameRGB->linesize);
                pFrameRGB->width = pCodecCtx->width;
                pFrameRGB->height = pCodecCtx->height;
                pFrameRGB->format = AV_PIX_FMT_RGB24;

                AVPacket pkt;
                av_init_packet(&pkt);

                pkt.data = NULL;
                pkt.size = 0;

                int got_packet = 0;

                AVCodecContext* pOutCodecCtx = avcodec_alloc_context3(NULL);

                avcodec_parameters_to_context(pOutCodecCtx, pCodecCtx->codecpar);

                pOutCodecCtx->codec_tag = 0;
                pOutCodecCtx->codec_id = AV_CODEC_ID_H264;

                pOutCodecCtx->width = pCodecCtx->width;
                pOutCodecCtx->height = pCodecCtx->height;
                pOutCodecCtx->pix_fmt = AV_PIX_FMT_YUV420P;

                avcodec_open2(pOutCodecCtx, pCodec, NULL);

                int ret = avcodec_encode_video2(pOutCodecCtx, &pkt, pFrameRGB, &got_packet);

                if (ret < 0) {
                    cout << "Error encoding video frame." << endl;
                    return -1;
                }

                if (got_packet) {
                    av_packet_rescale_ts(&pkt, pCodecCtx->time_base, pOutStream->time_base);
                    pkt.stream_index = pOutStream->index;

                    av_interleaved_write_frame(pOutFormatCtx, &pkt);
                    av_packet_unref(&pkt);
                }

                avcodec_free_context(&pOutCodecCtx);

                frameCount++;
            }
        }
        av_packet_unref(&packet);
    }

    av_write_trailer(pOutFormatCtx);
    avcodec_close(pCodecCtx);
    avformat_close_input(&pFormatCtx);

    if (buffer != NULL) {
        av_free(buffer);
    }

    if (pFrameRGB != NULL) {
        av_free(pFrameRGB);
    }

    if (pFrame != NULL) {
        av_free(pFrame);
    }

    if (pOutFormatCtx != NULL) {
        if (!(pOutFormatCtx->oformat->flags & AVFMT_NOFILE)) {
            avio_close(pOutFormatCtx->pb);
        }
        avformat_free_context(pOutFormatCtx);
    }

    return 0;
}

需要注意的是，这里使用的是FFmpeg库，因此需要在项目中添加FFmpeg的头文件和库文件，并且需要指定FFmpeg库的链接路径。具体使用方法可以参考FFmpeg的官方文档。另外，代码中的输入文件路径和输出文件路径需要根据实际情况修改。