使用FFmpeg库对视频资源进行格式转换

//导入头文件
#import "avformat.h"
#import "timestamp.h"
#import "avcodec.h"
#import "opt.h"
#import "samplefmt.h"
#import "swscale.h"
#import "avutil.h"

- (IBAction)remuxMultimediaAction:(id)sender {
    
    //需要处理的视频文件路径
    NSString * path = [[NSBundle mainBundle] pathForResource:@"test" ofType:@"mp4"];
    char  srcChar [ 1024 ];
    strcpy (srcChar ,( char  *)[path  UTF8String]);
    // 处理好的文件存储路径
    NSString * dstpath = [NSString stringWithFormat:@"%@/Library/Caches/1-1.flv",NSHomeDirectory()];
    char  dstChar [ 1024 ];
    strcpy (dstChar ,( char  *)[dstpath  UTF8String]);

    char * argv[2];
    argv[0] = srcChar;
    argv[1] = dstChar;
    
    NSLog(@"存储路径：%@", dstpath);
    remuxMultimedia(2, argv);
}

#pragma mark 格式转换
void remuxMultimedia(int argc, char* argv[]) {
    int ret = -1;
    int stream_idx = 0;
    int i = 0;

    //1. 处理一些参数；
    char* src;
    char* dst;

    int *stream_map = NULL;

    AVFormatContext *pFmtCtx = NULL;
    AVFormatContext *oFmtCtx = NULL;

    AVPacket pkt;

    av_log_set_level(AV_LOG_DEBUG);
    if (argc < 2)
    {
        av_log(NULL, AV_LOG_INFO, "arguments must be more than 2!\n");
        exit(-1);
    }

    src = argv[0];
    dst = argv[1];

    //2. 打开多媒体文件
    if((ret = avformat_open_input(&pFmtCtx, src, NULL, NULL)) < 0) {
        av_log(NULL, AV_LOG_ERROR, "%s\n", av_err2str(ret));
        exit(-1);
    }

    //4. 打开目的文件的上下文
    avformat_alloc_output_context2(&oFmtCtx, NULL, NULL, dst);
    if(!oFmtCtx){
        av_log(NULL, AV_LOG_ERROR, "NO MEMORY!\n");
        goto _ERROR;
    }

    stream_map = av_calloc(pFmtCtx->nb_streams, sizeof(int));
    if(!stream_map){
        av_log(NULL, AV_LOG_ERROR, "NO MEMORY!\n");
        goto _ERROR;
    }

    for(i=0; i < pFmtCtx->nb_streams; i++){
        AVStream *outStream = NULL;
        AVStream *inStream = pFmtCtx->streams[i];
        AVCodecParameters *inCodecPar = inStream->codecpar;
        if(inCodecPar->codec_type != AVMEDIA_TYPE_AUDIO &&
           inCodecPar->codec_type != AVMEDIA_TYPE_VIDEO &&
           inCodecPar->codec_type != AVMEDIA_TYPE_SUBTITLE)
        {
            stream_map[i] = -1;
            continue;
        }
        stream_map[i] = stream_idx++;

        //5. 为目的文件，创建一个新的视频流
        outStream = avformat_new_stream(oFmtCtx, NULL);
        if(!outStream){
            av_log(oFmtCtx, AV_LOG_ERROR, "NO MEMORY!\n");
            goto _ERROR;
        }

        avcodec_parameters_copy(outStream->codecpar, inStream->codecpar);
        outStream->codecpar->codec_tag = 0;
    }

    //绑定
    ret = avio_open2(&oFmtCtx->pb, dst, AVIO_FLAG_WRITE, NULL, NULL);
    if(ret < 0 ){
        av_log(oFmtCtx, AV_LOG_ERROR, "%s", av_err2str(ret));
        goto _ERROR;
    }

    //7. 写多媒体文件头到目的文件
    ret = avformat_write_header(oFmtCtx, NULL);
    if(ret < 0 ){
        av_log(oFmtCtx, AV_LOG_ERROR, "%s", av_err2str(ret));
        goto _ERROR;
    }
    //8. 从源多媒体文件中读取音频/视频/字幕数据到目的文件中
    while(av_read_frame(pFmtCtx, &pkt) >= 0) {
        AVStream *inStream, *outStream;

        inStream = pFmtCtx->streams[pkt.stream_index];
        if(stream_map[pkt.stream_index] < 0){
            av_packet_unref(&pkt);
            continue;
        }
        pkt.stream_index = stream_map[pkt.stream_index];

        outStream = oFmtCtx->streams[pkt.stream_index];
        av_packet_rescale_ts(&pkt, inStream->time_base, outStream->time_base);
        pkt.pos = -1;
        av_interleaved_write_frame(oFmtCtx, &pkt);
        av_packet_unref(&pkt);
        
    }
    //9. 写多媒体文件尾到文件中
    av_write_trailer(oFmtCtx);

    //10. 将申请的资源释放掉
_ERROR:
    if(pFmtCtx){
        avformat_close_input(&pFmtCtx);
        pFmtCtx = NULL;
    }
    if(oFmtCtx->pb){
        avio_close(oFmtCtx->pb);
    }

    if(oFmtCtx){
        avformat_free_context(oFmtCtx);
        oFmtCtx = NULL;
    }

    if(stream_map){
        av_free(stream_map);
    }
}