初始化视频流信息

- (instancetype)initWithVideo:(NSString *)moviePath
{
    if (!(self = [super init])) {
        return nil;
    }
    self.isNetwork = isNetworkPath(moviePath);
    if (self.isNetwork) {
        avformat_network_init();
    }
    AVCodec *pCodec;
    
    //注册所有的文件格式和编解码器
    avcodec_register_all();
    av_register_all();
    
    //打开视频文件
    /*打开输入流，四个参数1.获得文件名，这个函数读取文件的头部并且把信息保存到AVFormatContext结构体中，，fmt:如果非空,这个参数强制一个特定的输入格式。否则自动适应格式
     ##注释  将文件格式的上下文传递到AVFormatContext类型的结构体formatCtx中
     */
    if (avformat_open_input(&pFormatContext, [moviePath cStringUsingEncoding:NSASCIIStringEncoding], NULL, NULL)) {
        av_log(NULL, AV_LOG_ERROR, "Couldn't open file\n");
        goto initError;
    }
    //读取数据包获取流媒体文件的信息，每个AVStream存储一个视频/音频流的相关数据；每个AVStream对应一个AVCodecContext，存储该视频/音频流使用解码方式的相关数据 ##注释 查找文件中流的信息
    if (avformat_find_stream_info(pFormatContext, NULL) < 0) {
        av_log(NULL, AV_LOG_ERROR, "Couldn't find a video stream in the input");
        goto initError;
    }
    
    //find the first video stream
    if ((videoStream = av_find_best_stream(pFormatContext, AVMEDIA_TYPE_VIDEO, -1, -1, &pCodec, 0)) < 0) {
        av_log(NULL, AV_LOG_ERROR, "Cannot find a video stream in the input file\n");
        goto initError;
    }
    NSLog(@"videoStream:%d",videoStream);
    
    // find the audio stream;
    /*
     if ((audioStream = av_find_best_stream(pFormatContext, AVMEDIA_TYPE_AUDIO, -1, -1, &pCodec, 0))<0) {
     av_log(NULL, AV_LOG_ERROR, "Cannot find a audio stream in the input file\n");
     }
     */
    
    //Get a pointer to the codec context for the video stream
    pCodecContext = pFormatContext->streams[videoStream]->codec;
    //find the decoder for the video stream
    pCodec = avcodec_find_decoder(pCodecContext->codec_id);
    
    if (pCodec == NULL) {
        av_log(NULL, AV_LOG_ERROR, "Unsupported codec!\n");
        goto initError;
    }
    NSLog(@"Codec:%s",pCodec->name);
    
    //open codec
    if (avcodec_open2(pCodecContext, pCodec, NULL) < 0) {
        av_log(NULL, AV_LOG_ERROR, "Cannot open video decoder\n");
        goto initError;
    }
    
    pFrame = av_frame_alloc();
    
    self.outputWidth = pCodecContext->width;
    self.outputHeight = pCodecContext->height;
    NSLog(@"width,height,dur,%d,%d",self.outputWidth,self.outputHeight);
    return self;
    
initError:
    return nil;
}

播放:

- (NSArray *)playFrame
{
    NSLog(@"===================GO");
    //AVPacket packet;
    int frameFinished = 0; // 是否解析结束. 0:未结束 1:已结束
    
    NSLog(@"BEGIN --- while (!frameFinished && av_read_frame(pFormatContext, &packet)>=0)");
    while (!frameFinished && av_read_frame(pFormatContext, &packet)>=0) {
        NSLog(@"DOING --- while (!frameFinished && av_read_frame(pFormatContext, &packet)>=0)");
        //is this a packet from the video stream
        if (packet.stream_index == videoStream) {
            avcodec_decode_video2(pCodecContext, pFrame, &frameFinished, &packet);
        }
        NSLog(@"%lld",pFrame->pkt_duration);
    }
    
    return [NSArray arrayWithObjects:[NSNumber numberWithBool:(frameFinished != 0)] ,[self currentImage], nil];
}