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ffmpeg解码JPG和PNG等图片

分类： 嵌入式

2013-05-15 09:50:22

    【特别提醒：本文写作时，贴上去的代码，"\n"回车符号的"\"没有了，不知道为啥，所以阅读代码时请注意区分，或者欢迎到我的CSDN网站阅读
        http://blog.csdn.net/jgf_ntu/article/details/8928977】   
    一般我们都是用ffmpeg来解码音视频，如果是JPG和PNG等图片呢，其实跟解码视频是一样的，因为视频也是一幅一幅的图片进行解码的，只不过视频的帧是会前后参考的，而JPG等图片来讲，就是独立的一帧而已。
那么，我们参考之前的一篇文章http://blog.chinaunix.net/uid-25272011-id-3633434.html 【一段ffmpeg视频解码为YUV420P的示例代码】 ，稍作修改即可来演示。
    同时为了能够保存解码后的图片，我们还需要了解一些YUV或者RGB等各种格式的数据的内存存储方式，这些知识可以参照我之前的另一篇文章《YUV420格式解析》 ，这里详细描述了各种格式的空间存储机制。
    一般解码视频时，我们在调用ffmpeg进行解码时，生成的格式一般都是YUV420P的，但解码图皮时可能会有各种形式，如YUVJ422P、YUVJ444P、RGB24等等，本文没有采用ffmpeg的sws_scale函数做统一的转
换，为的是记录如何来存储这些解码后的图片。

     先给出如何从ffmpeg的Frame结构体中保存上述的四种解码后的数据：

点击(此处)折叠或打开

  1. /**
  2.  * save yuv420p frame [YUV]
  3.  */
  4. void yuv420p_save(AVFrame *pFrame, AVCodecContext *pCodecCtx)
  5. {
  6.     int i = 0;

  8.     int width = pCodecCtx->width, height = pCodecCtx->height;
  9.     int height_half = height / 2, width_half = width / 2;
  10.     int y_wrap = pFrame->linesize[0];
  11.     int u_wrap = pFrame->linesize[1];
  12.     int v_wrap = pFrame->linesize[2];

  14.     unsigned char *y_buf = pFrame->data[0];
  15.     unsigned char *u_buf = pFrame->data[1];
  16.     unsigned char *v_buf = pFrame->data[2];

  18.     //save y
  19.     for (i = 0; i < height; i++)
  20.         fwrite(y_buf + i * y_wrap, 1, width, pfout);
  21.     fprintf(stderr, "===>save Y successn");
  22.     //save u
  23.     for (i = 0; i < height_half; i++)
  24.         fwrite(u_buf + i * u_wrap, 1, width_half, pfout);
  25.     fprintf(stderr, "===>save U successn");
  26.     //save v
  27.     for (i = 0; i < height_half; i++)
  28.         fwrite(v_buf + i * v_wrap, 1, width_half, pfout);
  29.     fprintf(stderr, "===>save V successn");

  31.     fflush(pfout);
  32. }

  34. /**
  35.  * save yuv422p frame [YUV]
  36.  */
  37. void yuv422p_save(AVFrame *pFrame, AVCodecContext *pCodecCtx)
  38. {
  39.     int i = 0;

  41.     int width = pCodecCtx->width, height = pCodecCtx->height;
  42.     int height_half = height / 2, width_half = width / 2;
  43.     int y_wrap = pFrame->linesize[0];
  44.     int u_wrap = pFrame->linesize[1];
  45.     int v_wrap = pFrame->linesize[2];

  47.     unsigned char *y_buf = pFrame->data[0];
  48.     unsigned char *u_buf = pFrame->data[1];
  49.     unsigned char *v_buf = pFrame->data[2];

  51.     //save y
  52.     for (i = 0; i < height; i++)
  53.         fwrite(y_buf + i * y_wrap, 1, width, pfout);
  54.     fprintf(stderr, "===>save Y successn");
  55.     //save u
  56.     for (i = 0; i < height; i++)
  57.         fwrite(u_buf + i * u_wrap, 1, width_half, pfout);
  58.     fprintf(stderr, "===>save U successn");
  59.     //save v
  60.     for (i = 0; i < height; i++)
  61.         fwrite(v_buf + i * v_wrap, 1, width_half, pfout);
  62.     fprintf(stderr, "===>save V successn");

  64.     fflush(pfout);
  65. }

  67. /**
  68.  * save rgb24 frame [PPM]
  69.  */
  70. void rgb24_save(AVFrame *pFrame, AVCodecContext *pCodecCtx)
  71. {
  72.     int i = 0;
  73.     int width = pCodecCtx->width, height = pCodecCtx->height;
  74.     
  75.     /* write PPM header */
  76.     fprintf(pfout, "P6n%d %dn255n", width, height);
  77.   
  78.     /* write pixel data */
  79.     for(i =0; i < height; i++)
  80.         fwrite(pFrame->data[0] + i * pFrame->linesize[0], 1, width * 3, pfout);
  81.     
  82.     fflush(pfout);
  83. }

  85. /**
  86.  * save yuv444p frame [YUV]
  87.  */
  88. void yuv444p_save(AVFrame *pFrame, AVCodecContext *pCodecCtx)
  89. {
  90.     int i = 0;

  92.     int width = pCodecCtx->width, height = pCodecCtx->height;
  93.     int y_wrap = pFrame->linesize[0];
  94.     int u_wrap = pFrame->linesize[1];
  95.     int v_wrap = pFrame->linesize[2];

  97.     unsigned char *y_buf = pFrame->data[0];
  98.     unsigned char *u_buf = pFrame->data[1];
  99.     unsigned char *v_buf = pFrame->data[2];

  101.     //save y
  102.     for (i = 0; i < height; i++)
  103.         fwrite(y_buf + i * y_wrap, 1, width, pfout);
  104.     fprintf(stderr, "===>save Y successn");
  105.     //save u
  106.     for (i = 0; i < height; i++)
  107.         fwrite(u_buf + i * u_wrap, 1, width, pfout);
  108.     fprintf(stderr, "===>save U successn");
  109.     //save v
  110.     for (i = 0; i < height; i++)
  111.         fwrite(v_buf + i * v_wrap, 1, width, pfout);
  112.     fprintf(stderr, "===>save V successn");

  114.     fflush(pfout);
  115. }

     可以对照各种格式看一下代码，应该是很好理解的，下面是其余的main代码，可以编译运行

点击(此处)折叠或打开

  1. /**
  2.  * decode picture by ffmpeg-1.0 for jpg and png ...
  3.  *
  4.  * 2013-05-14
  5.  *    juguofeng<jgfntu@gmail.com>
  6.  */

  8. #include <stdlib.h>
  9. #include <stdio.h>
  10. #include <string.h>

  12. #include <libavcodec/avcodec.h>
  13. #include <libavformat/avformat.h>


  16. FILE *pfout = NULL;
  17. char ffrvout[128] = { 0 };

  19. /* how many yuv pic you want to save */
  20. #define FRAME_NUM 1
  21. /* enable video demux data save to file */
  22. //#define ENABLE_DEMUX_SAVE
  23. /* enable yuv pic save to file */
  24. #define ENABLE_YUV_SAVE
  25. /* enable print each video bytes */
  26. #define ENABLE_PRINT_FRAME_BYTES
  27. /* how many bytes you want to print */
  28. #define PRINT_BYTES 30


  31. /**
  32.  * main thread
  33.  */
  34. int main(int argc, char *argv[])
  35. {
  36.     int i;
  37.     char szFileName[128] = {0};
  38.     int decLen = 0;
  39.     int frame = 0;

  41.     AVCodecContext *pCodecCtx = NULL;
  42.     AVFrame *pFrame = NULL;
  43.     AVCodec *pCodec = NULL;
  44.     AVFormatContext *pFormatCtx = NULL;

  46.     if(argc != 3)
  47.     {
  48.         fprintf(stderr, "ERROR:need 3 argument!n");
  49.         exit(-1);
  50.     }
  51.     
  52.     sprintf(szFileName, "%s", argv[1]);

  54. #ifdef ENABLE_DEMUX_SAVE
  55.     FILE* frvdemux = fopen("rvdemuxout.rm","wb+");
  56.     if (NULL == frvdemux)
  57.     {
  58.         fprintf(stderr, "create rvdemuxout file failedn");
  59.         exit(1);
  60.     }
  61. #endif

  63.     /* output yuv file name */
  64.     sprintf(ffrvout, "%s", argv[2]);

  66.     pfout = fopen(ffrvout, "wb+");
  67.     if (NULL == pfout)
  68.     {
  69.         printf("create output file failedn");
  70.         exit(1);
  71.     }
  72.     printf("==========> Begin test ffmpeg call ffmpeg rv decodern");
  73.     av_register_all();

  75.     /* Open input video file */
  76.     //printf("before avformat_open_input [%s]n", szFileName);
  77.     if(avformat_open_input(&pFormatCtx, szFileName, NULL, NULL)!= 0)
  78.     {
  79.         fprintf(stderr, "Couldn't open input filen");
  80.         return -1;
  81.     }
  82.     //printf("after avformat_open_inputn");

  84.     /* Retrieve stream information */
  85.     if(av_find_stream_info(pFormatCtx) < 0)
  86.     {
  87.         printf("av_find_stream_info ERRORn");
  88.         return -1;
  89.     }
  90.     //printf("after av_find_stream_info, n");


  93.     /* Find the first video stream */
  94.     int videoStream = -1;
  95.     printf("==========> pFormatCtx->nb_streams = %dn", pFormatCtx->nb_streams);

  97.     for(i = 0; i < pFormatCtx->nb_streams; i++) {
  98.         if(pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
  99.             videoStream = i;
  100.             printf("the first video stream index: videoStream = %dn",videoStream);
  101.             break;
  102.         }
  103.     }

  105.     if(videoStream == -1)
  106.         return -1;        // Didn't find a video stream

  108.     /* Get a pointer to the codec context for the video stream */
  109.     pCodecCtx = pFormatCtx->streams[videoStream]->codec;
  110.     printf("pCodecCtx->codec_id = %dn", pCodecCtx->codec_id);

  112.     pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
  113.     if(pCodec == NULL) {
  114.         fprintf(stderr, "can not find decoder!n");
  115.         return -1;
  116.     }

  118.     /* Open codec */
  119.     if(avcodec_open(pCodecCtx, pCodec)<0)
  120.     {
  121.         printf("cannot open software codecn");
  122.         return -1; // Could not open codec
  123.     }
  124.     printf("==========> Open software codec successn");

  126.     pFrame = avcodec_alloc_frame();
  127.     if(pFrame == NULL)
  128.     {
  129.         fprintf(stderr, "avcodec_alloc_frame() ERRORn");
  130.         return -1;
  131.     }
  132.     
  133.     /* flag whether we get a decoded yuv frame */
  134.     int frameFinished;
  135.     int packetno = 0;

  137.     AVPacket packet;
  138.     av_init_packet(&packet);

  140.     while(av_read_frame(pFormatCtx, &packet) >= 0) {
  141.         //printf("[main]avpkt->slice_count=%dn", packet.sliceNum);

  143.         /* Is this a packet from the video stream? */
  144.         if(packet.stream_index == videoStream) {
  145.             packetno++;
  146. #ifdef ENABLE_PRINT_FRAME_BYTES
  147.         if ( 1 ) {
  148.             int i;
  149.             int size = packet.size < PRINT_BYTES ? packet.size : PRINT_BYTES;
  150.             unsigned char *data = packet.data;
  151.             printf("===>[%5d] [", packet.size);
  152.             for (i = 0; i < size; i++)
  153.                 printf("%02x ", data[i]);
  154.             printf("]n");
  155.         }
  156. #endif
  157. #ifdef ENABLE_DEMUX_SAVE
  158.             fwrite(packet.data, 1, packet.size, frvdemux);
  159. #endif
  160.             //printf("[the %d packet]packet.size = %dn", packetno++, packet.size);

  162.             while (packet.size > 0) {
  163.                 decLen = avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
  164.                 //printf("[video_decode_example]after avcodec_decode_video2,decoded=%dn",decLen);

  166.                 if (decLen < 0)    {
  167.                     fprintf(stderr, "[video_decode_example]Error while decoding frame %dn", frame);
  168.                     //exit(1);
  169.                     /* FIXME if decode one frame err, ignore this frame */
  170.                     decLen = packet.size;
  171.                 }

  173.                 if (frameFinished) {
  174.                     printf("got a yuv framen");
  175.                     //printf(stderr, "[video_decode_example]saving frame %3dn", frame);

  177.                     /* the picture is allocated by the decoder. no need to free it */
  178.                     if (frame == 0) {
  179.                         printf("[video_decode_example]picture->linesize[0]=%d, c->width=%d,c->height=%dn",
  180.                                 pFrame->linesize[0], pCodecCtx->width, pCodecCtx->height);
  181.                         printf("===>YUV format = %dn", pFrame->format);
  182.                     }
  183. #ifdef ENABLE_YUV_SAVE
  184.                     /* save yuv pic */
  185.                     if (frame < FRAME_NUM) {
  186.                         switch (pFrame->format) {
  187.                             case 0 :    /* YUV420P */
  188.                                 yuv420p_save(pFrame, pCodecCtx);
  189.                                 break;
  190.                             case 2 :    /* RGB24 */
  191.                                 rgb24_save(pFrame, pCodecCtx);
  192.                                 break;
  193.                             case 13 :    /* YUVJ422P */
  194.                                 yuv422p_save(pFrame, pCodecCtx);
  195.                                 break;
  196.                             case 14 :    /* YUVJ444P */
  197.                                 yuv444p_save(pFrame, pCodecCtx);
  198.                                 break;
  199.                             default :
  200.                                 fprintf(stderr, "unsupport YUV format for savingn");
  201.                                 break;
  202.                         }
  203.                         fprintf(stderr, "===>save pic successn");
  204.                     }
  205. #endif
  206.                     /* frame index grow */
  207.                     frame++;
  208.                 }
  209.                 //printf("===========> %dn", decLen);
  210.                 /* left data in pkt , go on decoding */
  211.                 packet.data += decLen;
  212.                 packet.size -= decLen;
  213.             }
  214.             if (frame == FRAME_NUM) {
  215.                 printf("==========> decoded [%d pkt frames] ---> save [%d YUV frames], enough to stop!n", packetno, FRAME_NUM);
  216.                 break;
  217.             }
  218.         }

  220.         /* FIXME no need free in this file */
  221.         //printf("free packet that was allocated by av_read_framen");
  222.         // Free the packet that was allocated by av_read_frame
  223.         //av_free_packet(&packet);
  224.     }

  226.     printf("decoding job down! begin to freen");
  227.     /* Free the YUV frame */
  228.     av_free(pFrame);

  230.     /* Close the codec */
  231.     avcodec_close(pCodecCtx);

  233.     /* Close the video file */
  234.     av_close_input_file(pFormatCtx);
  235.     fclose(pfout);

  237.     printf("==========> END-OKn");

  239.     return 0;
  240. }

     最后是Makefile文件

点击(此处)折叠或打开

  1. # use pkg-config for getting CFLAGS abd LDFLAGS
  2. FFMPEG_LIBS=libavdevice libavformat libavfilter libavcodec libswscale libavutil
  3. CFLAGS+=$(shell pkg-config --cflags $(FFMPEG_LIBS))
  4. LDFLAGS+=$(shell pkg-config --libs $(FFMPEG_LIBS))

  6. EXAMPLES=pic_dec

  8. OBJS=$(addsuffix .o,$(EXAMPLES))

  10. %: %.o
  11.     $(CC) $< $(LDFLAGS) -o $@

  13. %.o: %.c
  14.     $(CC) $< $(CFLAGS) -c -o $@

  16. .phony: all clean

  18. all: $(OBJS) $(EXAMPLES)

  20. clean:
  21.     rm -rf $(EXAMPLES) $(OBJS)

     注意如果是自己编译的ffmpeg-1.0等版本，安装到例如/usr/local/目录的话，需要在环境变量中设置
     PKG_CONFIG_PATH和LD_LIBRARY_PATH，指定到/usr/local/lib/pkgconfig和/usr/local/lib/目录（如果以后要利用你的PC来交叉编译如VLC等开源代码，最好将这两个变量注释掉，因为交叉编译时的configure脚本会根据
这个配置错误的检查到PC也就是X86结构的lib，这个显然是不对的，会让VLC模块错误的认为你的机子上有了一些第三方的库，但VLC并不知道这是X86结构的）
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给主人留下些什么吧！~~

jgfntu2013-05-15 13:32:57

/**
 * save rgb24 frame [PGM]
 */
void pgm_save(AVFrame *pFrame, AVCodecContext *pCodecCtx)
{
    int i;
 int width = pCodecCtx->width, height = pCodecCtx->height;
 
    fprintf(pfout,"P5\n%d %d\n%d\n", width, height, 255);
    
    for(i =0;i < height; i++)
        fwri

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jgfntu2013-05-15 12:28:15

不知到为啥，今天贴的代码，最后的“\n”的"\"没了，如果要复制代码的话，请到我的CSDN的网站吧
http://blog.csdn.net/jgf_ntu/article/details/8928977

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