FFmpeg实时解码H264

ffmpeg的解码过程在前面已经稍微总结了下，这里主要是测试一下用ffmpeg如何进行实时的解码。

在解码之前，我们先做好准备工作，调用摄像头。编码的过程中，进行入队出队操作，出队后的数据交给解码器，进行解码。

接下来依次介绍各个模块。

1.调用摄像头：

VideoCapture capture(0);int w = capture.get(CV_CAP_PROP_FRAME_WIDTH);
int h = capture.get(CV_CAP_PROP_FRAME_HEIGHT);
int yuv_bufLen = w * h * 3 / 2;
unsigned char* pYuvBuf = new unsigned char[yuv_bufLen];cout << "Frame size : " << w << " x " << h << endl;
namedWindow("opencamera", CV_WINDOW_AUTOSIZE);while (1)
{Mat frame;capture >> frame;imshow("opencamera", frame);if (waitKey(30) == 27) break;
}

怎么利用opencv调用摄像头，这里不做过多介绍，可以参考这里：点击打开链接。

2.编码过程：

DWORD WINAPI x264_encode(LPVOID lparam)
{VideoCapture capture(0);if (!capture.isOpened()){cout << "Cannot open the video cam" << endl;return -1;}int w = capture.get(CV_CAP_PROP_FRAME_WIDTH);int h = capture.get(CV_CAP_PROP_FRAME_HEIGHT);result_link_type* result_link = (result_link_type*)lparam;int yuv_bufLen = w * h * 3 / 2;//unsigned char* pYuvBuf = new unsigned char[yuv_bufLen];//int fps =25;size_t yuv_size = w * h * 3 / 2;x264_t *encoder;x264_picture_t pic_in, pic_out;uint8_t *yuv_buffer;x264_param_t param;//x264_param_default_preset(¶m, "veryfast", "zerolatency");  //为结构体param赋默认值x264_param_default_preset(¶m, "veryfast", "animation");//param.i_threads = 1;         //并行编码多帧param.i_width = w;           //视频图像的宽param.i_height = h;//  param.i_fps_num = fps;       //帧率分子//param.i_fps_den = 1;         //帧率分母 , fps_num / fps_den = 帧率//param.i_keyint_max = 50;     //IDR帧之间的间隔//param.b_intra_refresh = 1;   //是否使用周期帧内刷新IDR帧//param.b_annexb = 1;          //加前缀码0x00000001//param.rc.b_mb_tree = 0;      //实时编码必须为0，否则有延迟//param.b_sliced_threads = 0;//x264_param_apply_profile(¶m, "baseline");    //编码器的参数，使用baseline编码，可以跟上面的参数做冲突比较encoder = x264_encoder_open(¶m);     //打开编码器，初始化param#if 1x264_picture_alloc(&pic_in, X264_CSP_I420, w, h);    //为pic_in分配内存 yuv_buffer = (uint8_t*)malloc(yuv_size);     //给yuv_buffer分配内存pic_in.img.plane[0] = yuv_buffer;       //pic_in的三通道分别赋值pic_in.img.plane[1] = pic_in.img.plane[0] + w * h;pic_in.img.plane[2] = pic_in.img.plane[1] + w * h / 4;int64_t i_pts = 0;x264_nal_t *nals;int nnal;FILE *fp_out = fopen("test.h264", "wb");if (!fp_out){printf("Could not open output 264 file\n");return -1;}#if 1FILE* pFileOut = fopen("test.yuv", "w+");if (!pFileOut){printf("Could not open input yuv file\n");return -1;}
#endifcout << "Frame size : " << w << " x " << h << endl;namedWindow("opencamera", CV_WINDOW_AUTOSIZE);Mat frame;while (1){capture >> frame;             //摄像头处抓取一帧imshow("opencamera", frame);  //显示//if (waitKey(30) == 27) break;  waitKey(1);cv::Mat yuvImg;cv::cvtColor(frame, yuvImg, CV_BGR2YUV_I420);    //YUV转RGBmemcpy(yuv_buffer, yuvImg.data, yuv_bufLen*sizeof(unsigned char));    //YUV数据复制到yuv_buffer中//fwrite(yuv_buffer, yuv_bufLen*sizeof(unsigned char), 1, pFileOut);    //YUV写入本地//while (fread(yuv_buffer, 1, yuv_size, inf) > 0)//{pic_in.i_pts = i_pts++;x264_encoder_encode(encoder, &nals, &nnal, &pic_in, &pic_out);      //编码一帧数据x264_nal_t *nal;int j = 0;struct result_node_datatype *result_node = new struct result_node_datatype;result_node->result = new unsigned char[800000];memset(result_node->result, '\0', 800000);result_node->size = 0;for (nal = nals; nal < nals + nnal; nal++){//fwrite(nal->p_payload, 1, nal->i_payload, fp_out);      //产生的NAL保存在本地//result_node->size += nal->i_payload;//memcpy(result_node->result, nal->p_payload, nal->i_payload);//cout << "nal->i_payload = " <<nal->i_payload<< endl;//j = j + nal->i_payload;//result_push(result_link, result_node);//cout << "in for(nal)： j = "<<j << endl;memcpy(result_node->result + j, nal->p_payload, nal->i_payload);j = j + nal->i_payload;}result_node->size = j;cout << "result_node->size = " << result_node->size << endl;result_push(result_link, result_node);}x264_encoder_close(encoder);   //关闭编码器//fclose(inf);//free(yuv_buffer);//fclose(pFileOut);//delete[] pYuvBuf;//Sleep(100);
#endifreturn NULL;
}

X264编码的过程可以参考这里：点击打开链接。

需要注意的是，我们定义了一个为0的值j。编码产生后的NAL单元个数是nnal，编码后数据的起始地址是nal->p_payload，长度是nal->i_payload。增加j的原因是想把得到的一个个NAL单元累加在一起，组成一个完整帧的数据，最后一帧的长度就是j，然后将得到的一帧数据与长度送入队列，这是一个线程函数。对解码器来说，只有接收到完整的一帧，才能成功解码。

3.队列函数：

void result_push(result_link_type* result_link, result_node_datatype * result_node) //入队操作
{if (result_link->head == NULL){result_link->head = result_node;result_link->end = result_link->head;result_link->result_num++;//  cout << "0: result_link->result_num++" << endl;}else{result_link->end->next = result_node;result_link->end = result_node;result_link->result_num++;//    cout << "1: result_link->result_num++" << endl;}
}struct result_node_datatype* result_pop(result_link_type* result_link) //出队操作
{struct result_node_datatype* tmp_node;if (result_link->head == NULL)return NULL;else if (result_link->head == result_link->end){//    cout << "result_link->head == result_link->end " << endl;return NULL;}else{tmp_node = result_link->head;result_link->head = result_link->head->next;result_link->result_num--;//cout << "result_link->result_num--" << endl;return tmp_node;}
}

4.解码过程：

解码之前，要添加标志位0001。

bool get_h264_data(uchar* buf,int in_len,uchar* out_buf, int &out_len)
{char nalu[4] = { 0x00, 0x00, 0x00, 0x01 };memcpy(out_buf, nalu, 4);out_buf += 4;memcpy(out_buf, buf, in_len);out_len = in_len + 4;
//  cout << "out_len = " <<out_len<< endl;return true;
}

解码过程：

int main(int argc, char* argv[])
{HANDLE thread1;result_link_type *result_link = new result_link_type;result_link->head = result_link->end = NULL;result_link->result_num = 0;thread1 = CreateThread(NULL, 0, x264_encode, (LPVOID)result_link, 0, NULL);Sleep(1);//system("pause");
#if 1Mat pCvMat;AVCodec *pCodec;AVCodecContext *pCodecCtx = NULL;AVCodecParserContext *pCodecParserCtx = NULL;int frame_count;FILE *fp_in;FILE *fp_out;AVFrame    *pFrame, *pFrameYUV;uint8_t *out_buffer;
//  const int in_buffer_size = 4096;const int in_buffer_size = 800000;//uint8_t in_buffer[in_buffer_size + FF_INPUT_BUFFER_PADDING_SIZE] = { 0 };uint8_t in_buffer[in_buffer_size];memset(in_buffer, 0, sizeof(in_buffer));uint8_t *cur_ptr;int cur_size;AVPacket packet;int ret, got_picture;int y_size;AVCodecID codec_id = AV_CODEC_ID_H264;
//  char filepath_in[] = "test.h264";//  char filepath_out[] = "1.yuv";int first_time = 1;struct SwsContext *img_convert_ctx;//av_log_set_level(AV_LOG_DEBUG);avcodec_register_all();pCodec = avcodec_find_decoder(codec_id);if (!pCodec) {printf("Codec not found\n");return -1;}pCodecCtx = avcodec_alloc_context3(pCodec);if (!pCodecCtx){printf("Could not allocate video codec context\n");return -1;}pCodecParserCtx = av_parser_init(codec_id);if (!pCodecParserCtx){printf("Could not allocate video parser context\n");return -1;}if (pCodec->capabilities&CODEC_CAP_TRUNCATED)pCodecCtx->flags |= CODEC_FLAG_TRUNCATED; /* we do not send complete frames */if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0) {printf("Could not open codec\n");return -1;}
#if 0//Input Filefp_in = fopen(filepath_in, "rb");if (!fp_in) {printf("Could not open input stream\n");return -1;}//Output Filefp_out = fopen(filepath_out, "wb");if (!fp_out) {printf("Could not open output YUV file\n");return -1;}
#endifpFrame = av_frame_alloc();av_init_packet(&packet);AVFrame* pFrameBGR = av_frame_alloc(); //存储解码后转换的RGB数据  // 保存BGR，opencv中是按BGR来保存的  int size;//cout << "pCodecCtx->width = " << pCodecCtx->width << "\npCodecCtx->height = " << pCodecCtx->height << endl;//pCvMat.create(cv::Size(pCodecCtx->width, pCodecCtx->height), CV_8UC3);struct result_node_datatype *result_node2 = NULL;int out_len;while (1) {// cur_size = fread(in_buffer, 1, in_buffer_size, fp_in);//   cout << "result_link->size = " << result_link->result_num << endl;result_node2 = result_pop(result_link);if (result_node2 == NULL){Sleep(1);//    cout << "result_node2 is NULL" << endl;continue;}//cur_size = result_node2->size;//cout<<"after result_pop()" << endl;get_h264_data(result_node2->result, result_node2->size, in_buffer, out_len);//cur_size = result_node2->size;cur_size = out_len;cout << "cur_size = " << cur_size << endl;if (cur_size == 0)break;cur_ptr = in_buffer;//cur_ptr = result_node2->result;while (cur_size>0){int len = av_parser_parse2(pCodecParserCtx, pCodecCtx,&packet.data, &packet.size,cur_ptr, cur_size,AV_NOPTS_VALUE, AV_NOPTS_VALUE, AV_NOPTS_VALUE);cur_ptr += len;cur_size -= len;if (packet.size == 0)continue;//Some Info from AVCodecParserContextprintf("Packet Size:%6d\t", packet.size);switch (pCodecParserCtx->pict_type){case AV_PICTURE_TYPE_I: printf("Type: I\t"); break;case AV_PICTURE_TYPE_P: printf("Type: P\t"); break;case AV_PICTURE_TYPE_B: printf("Type: B\t"); break;default: printf("Type: Other\t"); break;}printf("Output Number:%4d\t", pCodecParserCtx->output_picture_number);printf("Offset:%8ld\n", pCodecParserCtx->cur_offset);ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, &packet);if (ret < 0) {printf("Decode Error.(解码错误)\n");return ret;}if (got_picture) {if (first_time){printf("\nCodec Full Name:%s\n", pCodecCtx->codec->long_name);printf("width:%d\nheight:%d\n\n", pCodecCtx->width, pCodecCtx->height);//SwsContext//img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,//   pCodecCtx->width, pCodecCtx->height, PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_BGR24, SWS_BICUBIC, NULL, NULL, NULL);//pFrameYUV = av_frame_alloc();//out_buffer = (uint8_t *)av_malloc(avpicture_get_size(PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height));//avpicture_fill((AVPicture *)pFrameYUV, out_buffer, PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height);//y_size = pCodecCtx->width*pCodecCtx->height;//size = avpicture_get_size(AV_PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height);size = avpicture_get_size(AV_PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height);out_buffer = (uint8_t *)av_malloc(size);avpicture_fill((AVPicture *)pFrameBGR, out_buffer, AV_PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height); // allocator memory for BGR buffer  cout << "pCodecCtx->width = " << pCodecCtx->width << "\npCodecCtx->height = " << pCodecCtx->height << endl;pCvMat.create(cv::Size(pCodecCtx->width, pCodecCtx->height), CV_8UC3);first_time = 0;}printf("Succeed to decode 1 frame!\n");//sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height,pFrameYUV->data, pFrameYUV->linesize);sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameBGR->data, pFrameBGR->linesize);//fwrite(pFrameYUV->data[0], 1, y_size, fp_out);     //Y //fwrite(pFrameYUV->data[1], 1, y_size / 4, fp_out);   //U//fwrite(pFrameYUV->data[2], 1, y_size / 4, fp_out);   //Vcout << "size = " << size << endl;memcpy(pCvMat.data, out_buffer, size);imshow("RGB", pCvMat);waitKey(1);}}}system("pause");//Flush Decoderpacket.data = NULL;packet.size = 0;#if 0while (1){ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, &packet);if (ret < 0) {printf("Decode Error.(解码错误)\n");return ret;}if (!got_picture)break;if (got_picture) {printf("Flush Decoder: Succeed to decode 1 frame!\n");sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height,pFrameYUV->data, pFrameYUV->linesize);fwrite(pFrameYUV->data[0], 1, y_size, fp_out);     //Yfwrite(pFrameYUV->data[1], 1, y_size / 4, fp_out);   //Ufwrite(pFrameYUV->data[2], 1, y_size / 4, fp_out);   //V}}
#endif//    fclose(fp_in);
//  fclose(fp_out);sws_freeContext(img_convert_ctx);av_parser_close(pCodecParserCtx);//av_frame_free(&pFrameYUV);av_frame_free(&pFrameBGR);av_frame_free(&pFrame);avcodec_close(pCodecCtx);av_free(pCodecCtx);
#endifreturn 0;
}

解码流程以及基本参数和函数的意义，可以参考链接：点击打开链接。

解码成功后，got_picture为非零值，在这个判断里面，解码出的数据转为RGB格式，并用opencv显示出来。

运行效果图：

运行的过程中，对比上面的效果图，发现解码后的图像比摄像头要延迟几秒钟，这是因为在编码的过程，我们使用了参数animation，编码开始前会缓存几帧，再开始，这样帧间编码效果好，压缩效率高。如果使用zerolatency（零延时），基本不会有延时效果，但是压缩效果不太好。

完整测试项目的代码下载地址：点击打开链接

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