使用FFmpeg库对视频资源进行裁剪

#import "avformat.h"
#import "timestamp.h"
#import "avcodec.h"
#import "opt.h"
#import "samplefmt.h"
#import "swscale.h"
#import "avutil.h"

static void log_packet(AVFormatContext *fmtCtx, const AVPacket *pkt, int64_t pts_start, int64_t dts_start){
    // = &fmtCtx->streams[pkt->stream_index]->time_base;
    av_log(fmtCtx,
           AV_LOG_INFO,
           "pts:%s dts:%s pts_diff:%lld dts_diff:%lld stream_idx:%d pts_start:%lld dts_start:%lld\n",
           av_ts2str(pkt->pts),
           av_ts2str(pkt->dts),
           pkt->pts - pts_start,
           pkt->dts - dts_start,
           pkt->stream_index,
           pts_start,
           dts_start);
}

- (IBAction)cutMultimediaAction:(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/1-2.mp4",NSHomeDirectory()];
    char  dstChar [ 1024 ];
    strcpy (dstChar ,( char  *)[dstpath  UTF8String]);
    // 截取的开始时间点
    NSString * start = @"10.0";
    char  startChar [ 1024 ];
    strcpy (startChar ,( char  *)[start  UTF8String]);
    // 截取的结束时间点
    NSString * end = @"30.0";
    char  endChar [ 1024 ];
    strcpy (endChar ,( char  *)[end  UTF8String]);
    
    char * argv[4];
    argv[0] = srcChar;
    argv[1] = dstChar;
    argv[2] = startChar;
    argv[3] = endChar;
    
    NSLog(@"存储路径：%@", dstpath);
    cutMultimedia(4, argv);
}

#pragma mark 视频裁剪
void cutMultimedia(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;

    double starttime = 0;
    double endtime = 0;

    int *stream_map = NULL;
    int64_t *dts_start_time = NULL;
    int64_t *pts_start_time = NULL;


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

    AVPacket pkt;

    av_log_set_level(AV_LOG_DEBUG);

    //cut src dst start end
    if(argc < 4){
        av_log(NULL, AV_LOG_INFO, "arguments must be more than 4!\n");
        exit(-1);
    }

    src = argv[0];
    dst = argv[1];
    starttime = atof(argv[2]);
    endtime = atof(argv[3]);

    //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;
    }

    //seek
    ret = av_seek_frame(pFmtCtx, -1, starttime*AV_TIME_BASE, AVSEEK_FLAG_BACKWARD);
    if(ret < 0) {
        av_log(oFmtCtx, AV_LOG_ERROR, "%s", av_err2str(ret));
        goto _ERROR;
    }

    dts_start_time = av_calloc(pFmtCtx->nb_streams, sizeof(int64_t));
    for(int t=0; t < pFmtCtx->nb_streams; t++){
        dts_start_time[t] = -1;
    }
    pts_start_time = av_calloc(pFmtCtx->nb_streams, sizeof(int64_t));
     for(int t=0; t < pFmtCtx->nb_streams; t++){
        pts_start_time[t] = -1;
    }

    //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;

        if(dts_start_time[pkt.stream_index] == -1 && pkt.dts >= 0){
            dts_start_time[pkt.stream_index] = pkt.dts;
        }

        if(pts_start_time[pkt.stream_index] == -1 && pkt.pts >= 0){
            pts_start_time[pkt.stream_index] = pkt.pts;
        }

        inStream = pFmtCtx->streams[pkt.stream_index];

        if(av_q2d(inStream->time_base) * pkt.pts > endtime) {
            av_log(oFmtCtx, AV_LOG_INFO, "success!\n");
            break;
        }
        if(stream_map[pkt.stream_index] < 0){
            av_packet_unref(&pkt);
            continue;
        }
        //printf("pkt.pts=%lld, pkt.dts=%lld\n", pkt.pts, pkt.dts);
        log_packet(pFmtCtx, &pkt, pts_start_time[pkt.stream_index], dts_start_time[pkt.stream_index]);

        pkt.pts = pkt.pts - pts_start_time[pkt.stream_index];
        pkt.dts = pkt.dts - dts_start_time[pkt.stream_index];


        if(pkt.dts > pkt.pts){
            pkt.pts = pkt.dts;
        }

        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);
    }

    if(dts_start_time){
        av_free(dts_start_time);
    }

    if(pts_start_time){
        av_free(pts_start_time);
    }
}