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;
}
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 1
x264_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 1
FILE* pFileOut = fopen("test.yuv", "w+");
if (!pFileOut)
{
printf("Could not open input yuv file\n");
return -1;
}
#endif
cout << "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RGB
memcpy(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);
#endif
return 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 1
Mat 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 File
fp_in = fopen(filepath_in, "rb");
if (!fp_in) {
printf("Could not open input stream\n");
return -1;
}
//Output File
fp_out = fopen(filepath_out, "wb");
if (!fp_out) {
printf("Could not open output YUV file\n");
return -1;
}
#endif
pFrame = 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 AVCodecParserContext
printf("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); //V
cout << "size = " << size << endl;
memcpy(pCvMat.data, out_buffer, size);
imshow("RGB", pCvMat);
waitKey(1);
}
}
}
system("pause");
//Flush Decoder
packet.data = NULL;
packet.size = 0;
#if 0
while (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); //Y
fwrite(pFrameYUV->data[1], 1, y_size / 4, fp_out); //U
fwrite(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);
#endif
return 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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