二、mp4转wmv项目讲解

本文用到的函数:

序号	函数名	参数	注释
1	av_register_all	void av_register_all(void)	注册所有的封装器和解封器
2	avformat_open_input	int avformat_open_input(AVFormatContext **ps, const char *url, AVInputFormat *fmt, AVDictionary **options)	创建一个输入的上下文环境
3	avformat_alloc_output_context2	int avformat_alloc_output_context2(AVFormatContext **ctx, AVOutputFormat *oformat,const char *format_name, const char *filename);	创建一个输出的上下文环境
4	avformat_new_stream	AVStream *avformat_new_stream(AVFormatContext *s, const AVCodec *c)	在指定上下文中插入一个Stream成员
5	avcodec_parameters_copy	int avcodec_parameters_copy(AVCodecParameters *dst, const AVCodecParameters *src)	copyAVCodec的上下文
6	avio_open	int avio_open(AVIOContext **s, const char *url, int flags)	打开FFmpeg的输入输出文件
7	avformat_write_header	int avformat_write_header(AVFormatContext *s, AVDictionary **options)	写视频文件头
8	av_read_frame	int av_read_frame(AVFormatContext *s, AVPacket *pkt)	读入指定上下文的一帧
9	av_rescale_q_rnd	int64_t av_rescale_q_rnd(int64_t a, AVRational bq, AVRational cq,enum AVRounding rnd)	换算比例
10	av_write_frame	int av_write_frame(AVFormatContext *s, AVPacket *pkt)	向指定上下文写入一帧
11	av_packet_unref	void av_packet_unref(AVPacket *pkt)	释放AVPacket内存
12	av_write_trailer	int av_write_trailer(AVFormatContext *s)	写视频文件尾
13	avio_close	int avio_close(AVIOContext *s)	关闭FFmpeg的输入输出文件

0001.jpg

#include <iostream>
extern "C" {
#include<libavformat/avformat.h>
#include<libavcodec/avcodec.h>
}
#pragma comment(lib,"avformat.lib")
#pragma comment(lib,"avcodec.lib")
#pragma comment(lib,"avutil.lib")
using namespace std;
int main()
{
    char infile[] = "2.mp4";
    char outfile[] = "output.mov";
    av_register_all();//注册所有的封装器和解封器
    AVFormatContext* inputFormatCtx = NULL;
    avformat_open_input(&inputFormatCtx, infile, NULL, NULL);
    if (!inputFormatCtx) {
        printf("open file fail!\n");
        return -1;
    }
    
    AVFormatContext* outputFormatCtx = NULL;
    avformat_alloc_output_context2(&outputFormatCtx, NULL, NULL, outfile);
    if (!outputFormatCtx){
        printf("create OutputCtx fail!\n");
        return -2;
    }
    AVStream *videoStream = avformat_new_stream(outputFormatCtx, NULL);
    AVStream *audioStream= avformat_new_stream(outputFormatCtx, NULL);
    avcodec_parameters_copy(videoStream->codecpar, inputFormatCtx->streams[0]->codecpar);
    avcodec_parameters_copy(audioStream->codecpar, inputFormatCtx->streams[0]->codecpar);
    videoStream->codecpar->codec_type = AVMEDIA_TYPE_VIDEO;
    audioStream->codecpar->codec_type = AVMEDIA_TYPE_VIDEO;
    av_dump_format(inputFormatCtx, 0, infile, 0);
    printf("============================================");
    av_dump_format(outputFormatCtx, 0, outfile, 1);
    
    int ret=avio_open(&outputFormatCtx->pb, outfile, AVIO_FLAG_WRITE);
    if (ret < 0) {
        printf("avio open failed!\n");
        return -3;
    }
    avformat_write_header(outputFormatCtx, NULL);
    if (ret < 0)
    {
        printf("write header failed!\n");
        
    }
    AVPacket pkt;
    int i = 0;
    for (;;) 
    {

        ret=av_read_frame(inputFormatCtx, &pkt);
        if (ret < 0) {
            break;
        }
        pkt.pts=av_rescale_q_rnd(pkt.pts,
            inputFormatCtx->streams[pkt.stream_index]->time_base,
            outputFormatCtx->streams[pkt.stream_index]->time_base,
            (AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX));
        pkt.dts=av_rescale_q_rnd(pkt.dts,
            inputFormatCtx->streams[pkt.stream_index]->time_base,
            outputFormatCtx->streams[pkt.stream_index]->time_base,
            (AVRounding)(AV_ROUND_NEAR_INF | AV_ROUND_PASS_MINMAX));
        pkt.pos = -1;
        pkt.duration= av_rescale_q_rnd(pkt.duration,
            inputFormatCtx->streams[pkt.stream_index]->time_base,
            outputFormatCtx->streams[pkt.stream_index]->time_base,
            (AVRounding)(AV_ROUND_NEAR_INF | AV_ROUND_PASS_MINMAX));
        av_write_frame(outputFormatCtx, &pkt);
        av_packet_unref(&pkt);
        cout <<".";
    }
    cout << "\n=========================" << endl;
    av_write_trailer(outputFormatCtx);
    avio_close(outputFormatCtx->pb);

}