1.安装FFMpeg

pod 'mobile-ffmpeg-full'

1.FFMpeg解码步骤

1.通过url 和传输方式初始化解码器

static AVFormatContext *fmt_ctx;
static AVCodecContext *dec_ctx;
static int video_stream_index = -1;
static int init_rtsp_with_url(char *url,char *transport){
    const AVCodec *dec;
    int ret;
    
    AVDictionary *opts = 0;
    av_dict_set(&opts, "rtsp_transport", "tcp", 0);
    if ((ret = avformat_open_input(&fmt_ctx, url, NULL, NULL)) < 0) {
        av_log(NULL, AV_LOG_ERROR, "打开流媒体失败\n");
        return ret;
    }
    
    if ((ret = avformat_find_stream_info(fmt_ctx, NULL)) < 0) {
        av_log(NULL, AV_LOG_ERROR, "无法提取流信息\n");
        return ret;
    }
    
    /* select the video stream */
    ret = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, &dec, 0);
    if (ret < 0) {
        av_log(NULL, AV_LOG_ERROR, "找不到视频流\n");
        return ret ;
    }
    video_stream_index = ret;
    /* create decoding context */
    dec_ctx = avcodec_alloc_context3(dec);
    if (!dec_ctx){
        
        return AVERROR(ENOMEM);
    }
    avcodec_parameters_to_context(dec_ctx, fmt_ctx->streams[video_stream_index]->codecpar);
    
    /* init the video decoder */
    if ((ret = avcodec_open2(dec_ctx, dec, NULL)) < 0) {
        av_log(NULL, AV_LOG_ERROR, "无法打开解码器\n");
        return  ret;
    }
    
    return  0;
}

2.创建循环线程 用于解码frame

AVPacket *packet;
AVFrame *frame;

void * run(void *param)    // 新线程调用方法，里边为需要执行的任务
{
    int ret;
    
    
    H264YUV_Frame yuvFrame;
    memset(&yuvFrame, 0, sizeof(H264YUV_Frame));
    
    /***读取视频流***/
    frame = av_frame_alloc();
    packet = av_packet_alloc();
    while (1) {
        if ((ret = av_read_frame(fmt_ctx, packet)) < 0)
            break;
        
        if (packet->stream_index == video_stream_index) {
            ret = avcodec_send_packet(dec_ctx, packet);
            if (ret < 0) {
                av_log(NULL, AV_LOG_ERROR, "Error while sending a packet to the decoder\n");
                break;
            }
            
            while (ret >= 0) {
                ret = avcodec_receive_frame(dec_ctx, frame);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                    break;
                } else if (ret < 0) {
                    av_log(NULL, AV_LOG_ERROR, "Error while receiving a frame from the decoder\n");
                    goto end;
                }
                
                frame->pts = frame->best_effort_timestamp;
                
                
                yuvFrame = decodeToYUV(dec_ctx, frame);
               //回调函数 用于渲染yuv
                (*yuvCallBack)(yuvFrame);
                
               
                
                av_frame_unref(frame);
            }
        }
        av_packet_unref(packet);
    }
    
end:

   close_rtsp();

    return NULL;
}

释放解码器

void close_rtsp(void){
    avcodec_free_context(&dec_ctx);
    avformat_close_input(&fmt_ctx);
    av_frame_free(&frame);
    av_packet_free(&packet);
}

frame 转为 yuv 结构体可以自己定义

typedef struct H264FrameDef
{
    unsigned int    length;
    unsigned char*  dataBuffer;
    
}H264Frame;

typedef struct  H264YUVDef
{
    unsigned int    width;
    unsigned int    height;
    H264Frame       luma;
    H264Frame       chromaB;
    H264Frame       chromaR;
    
}H264YUV_Frame;
void copyDecodedFrame(unsigned char *src, unsigned char *dist,int linesize, int width, int height)
{
    width = fminf(linesize, width);
    for (int i = 0; i < height; ++i)
    {
        memcpy(dist, src, width);
        dist += width;
        src += linesize;
    }
}

H264YUV_Frame decodeToYUV(AVCodecContext *dec_ctx, AVFrame *frame){
    
    unsigned int lumaLength= (dec_ctx->height)*(fminf(frame->linesize[0], dec_ctx->width));
    unsigned int chromBLength=((dec_ctx->height)/2)*(fminf(frame->linesize[1], (dec_ctx->width)/2));
    unsigned int chromRLength=((dec_ctx->height)/2)*(fminf(frame->linesize[2], (dec_ctx->width)/2));
     
    H264YUV_Frame yuvFrame;
    memset(&yuvFrame, 0, sizeof(H264YUV_Frame));
    yuvFrame.luma.length = lumaLength;
    yuvFrame.chromaB.length = chromBLength;
    yuvFrame.chromaR.length =chromRLength;
    yuvFrame.luma.dataBuffer=(unsigned char*)malloc(lumaLength);
    yuvFrame.chromaB.dataBuffer=(unsigned char*)malloc(chromBLength);
    yuvFrame.chromaR.dataBuffer=(unsigned char*)malloc(chromRLength);
    
    copyDecodedFrame(frame->data[0],yuvFrame.luma.dataBuffer,frame->linesize[0],
                     dec_ctx->width,dec_ctx->height);
    copyDecodedFrame(frame->data[1], yuvFrame.chromaB.dataBuffer,frame->linesize[1],
                     dec_ctx->width / 2,dec_ctx->height / 2);
    copyDecodedFrame(frame->data[2], yuvFrame.chromaR.dataBuffer,frame->linesize[2],
                     dec_ctx->width / 2,dec_ctx->height / 2);
    
    yuvFrame.width=dec_ctx->width;
    yuvFrame.height=dec_ctx->height;

    return yuvFrame;

}