ffmpeg 解码

static void pgm_save(unsigned char *buf, int wrap, int xsize, int ysize,char*filename){    FILE *f;    int i;     f=fopen(filename,"wb");    fprintf(f,"P5\n%d%d\n%d\n",xsize,ysize,255);    for(i=0;i<ysize;i++)        fwrite(buf + i * wrap,1,xsize,f);    fclose(f);}  //通过查找0x000001或者0x00000001找到下一个数据包的头部static int _find_head(unsigned char*buffer, int len){    int i;     for(i=512;i<len;i++)    {        if(buffer[i] == 0 && buffer[i+1] == 0 && buffer[i+2] == 0&& buffer[i+3] == 1)            break;        if(buffer[i]== 0 && buffer[i+1] == 0 && buffer[i+2] == 1)            break;    }    if (i ==len)        return0;    if (i ==512)        return0;    return i;}   //将文件中的一个数据包转换成AVPacket类型以便ffmpeg进行解码#define FILE_READING_BUFFER (1*1024*1024)static void build_avpkt(AVPacket *avpkt, FILE *fp){    static unsigned charbuffer[1*1024*1024];    static int readptr = 0;    static int writeptr = 0;    intlen,toread;     intnexthead;     if (writeptr- readptr < 200 * 1024)    {        memmove(buffer, &buffer[readptr],writeptr - readptr);        writeptr -= readptr;        readptr = 0;        toread = FILE_READING_BUFFER - writeptr;        len = fread(&buffer[writeptr], 1,toread, fp);        writeptr += len;    }     nexthead = _find_head(&buffer[readptr], writeptr-readptr);    if (nexthead== 0)    {        printf("failedfind next head...\n");        nexthead = writeptr - readptr;    }     avpkt->size = nexthead;    avpkt->data = &buffer[readptr];    readptr += nexthead; } static voidvideo_decode_example(const char *outfilename, constchar *filename){    AVCodec *codec;    AVCodecContext *c= NULL;    int frame,got_picture, len;    FILE *f, *fout;    AVFrame *picture;    uint8_t inbuf[INBUF_SIZE +FF_INPUT_BUFFER_PADDING_SIZE];    charbuf[1024];    AVPacket avpkt;     av_init_packet(&avpkt);     /* set end ofbuffer to 0 (this ensures that no overreading happens for damaged mpeg streams)*/    memset(inbuf + INBUF_SIZE, 0,FF_INPUT_BUFFER_PADDING_SIZE);     printf("Videodecoding\n");    opts = NULL;    //av_dict_set(&opts,"b", "2.5M", 0);    /* find the h264video decoder */    codec = avcodec_find_decoder(CODEC_ID_H264);    if (!codec){        fprintf(stderr, "codecnot found\n");        return ;    }     c = avcodec_alloc_context3(codec);    picture= avcodec_alloc_frame();     if(codec->capabilities&CODEC_CAP_TRUNCATED)    c->flags|= CODEC_FLAG_TRUNCATED; /* we do not send complete frames */     /* For somecodecs, such as msmpeg4 and mpeg4, width and height    MUST be initialized there because thisinformation is not    available in the bitstream. */     /* open it */    if(avcodec_open2(c, codec, NULL) < 0) {        fprintf(stderr, "couldnot open codec\n");        exit(1);    }  //  fout=fopen(outfilename,"wb");    /* the codec givesus the frame size, in samples */     f = fopen(filename, "rb");    if (!f) {        fprintf(stderr, "couldnot open %s\n", filename);        exit(1);    }     //解码与显示需要的辅助的数据结构，需要注意的是，AVFrame必须经过alloc才能使用，不然其内存的缓存空间指针是空的，程序会崩溃    AVFrame frameRGB;    IplImage *showImage =cvCreateImage(cvSize(352,288),8,3);    avpicture_alloc((AVPicture*)&frameRGB,PIX_FMT_RGB24,352,288);    cvNamedWindow("decode");     frame = 0;    for(;;) {         build_avpkt(&avpkt, f);         if(avpkt.size == 0)            break;         while(avpkt.size > 0) {            len = avcodec_decode_video2(c,picture, &got_picture, &avpkt);//解码每一帧            if(len < 0) {                fprintf(stderr, "Error while decoding frame %d\n",frame);                break;            }            if(got_picture) {                printf("savingframe %3d\n", frame);                fflush(stdout);                 /* thepicture is allocated by the decoder. no need to free it */               //将YUV420格式的图像转换成RGB格式所需要的转换上下文                SwsContext* scxt =sws_getContext(picture->width,picture->height,PIX_FMT_YUV420P,                                                  picture->width,picture->height,PIX_FMT_RGB24,                                                  2,NULL,NULL,NULL);                if(scxt != NULL)                {                    sws_scale(scxt,picture->data,picture->linesize,0,c->height,frameRGB.data,frameRGB.linesize);//图像格式转换                    showImage->imageSize =frameRGB.linesize[0];//指针赋值给要显示的图像                    showImage->imageData = (char *)frameRGB.data[0];                    cvShowImage("decode",showImage);//显示                    cvWaitKey(0.5);//设置0.5s显示一帧，如果不设置由于这是个循环，会导致看不到显示出来的图像                }                 //sprintf(buf,outfilename,frame);                 //pgm_save(picture->data[0],picture->linesize[0],                //c->width,c->height, buf);                //pgm_save(picture->data[1],picture->linesize[1],                //c->width/2,c->height/2, fout);                //pgm_save(picture->data[2],picture->linesize[2],                //c->width/2,c->height/2, fout);                frame++;            }            avpkt.size -= len;            avpkt.data += len;        }    }     /* some codecs,such as MPEG, transmit the I and P frame with a    latency of one frame. You must do thefollowing to have a    chance to get the last frame of the video */    avpkt.data = NULL;    avpkt.size = 0;    len = avcodec_decode_video2(c, picture,&got_picture, &avpkt);    if(got_picture) {        printf("savinglast frame %3d\n", frame);        fflush(stdout);         /* the pictureis allocated by the decoder. no need to        free it */        sprintf(buf, outfilename, frame);        //pgm_save(picture->data[0],picture->linesize[0],        //       c->width, c->height, fout);        pgm_save(picture->data[0],picture->linesize[0],c->width, c->height, fout);        pgm_save(picture->data[1],picture->linesize[1],c->width/2, c->height/2, fout);        pgm_save(picture->data[2],picture->linesize[2],c->width/2, c->height/2, fout);         frame++;    }     fclose(f);//  fclose(fout);     avcodec_close(c);    av_free(c);    av_free(picture);    printf("\n");}  int main(int argc, char* argv[]){    avcodec_register_all();//注册所有的编解码器，一定要注意，如果没有这行代码则会出错，提示没有找不到编解码器    video_decode_example("%3d.pgm","test.264");//可以使用x264编码出来的264文件    system("pause");    return 0;}