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• how to change the frame rate and capturing image size from IP camera

  6 décembre 2015, par rockycai

  Now I have a IP camera and I want to capture image from it through RTSP.I use below code and it works well.But the camera’s frame rate is 25/s.So I got a lot of images per second.I don’t want it.And per image is 6.2MB.I also don’t want need to get high quality image.What can I do to slower the frame rate and smaller the size of image ?

  #ifndef INT64_C
  
  #define INT64_C(c) (c ## LL)
  
  #define UINT64_C(c) (c ## ULL)
  
  #endif
  
  
  
  #ifdef __cplusplus
  
  extern "C" {
  
  #endif
  
      /*Include ffmpeg header file*/
  
  #include <libavformat></libavformat>avformat.h>
  
  #include <libavcodec></libavcodec>avcodec.h>
  
  #include <libswscale></libswscale>swscale.h>
  
  #include 
  
  #ifdef __cplusplus
  
  }
  
  #endif
  
  
  
  #include 
  
  
  
  
  
  static void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame);
  
  
  
  int main (int argc, const char * argv[])
  
  {
  
      AVFormatContext *pFormatCtx;
  
      int             i, videoStream;
  
      AVCodecContext  *pCodecCtx;
  
      AVCodec         *pCodec;
  
      AVFrame         *pFrame; 
  
      AVFrame         *pFrameRGB;
  
      AVPacket        packet;
  
      int             frameFinished;
  
      int             numBytes;
  
      uint8_t         *buffer;
  
  
  
      // Register all formats and codecs
  
      av_register_all();
  
  //  const char *filename="C:\libraries\gfjyp.avi";
  
      // Open video file
  
      //AVDictionary *options = NULL;
  
      //av_dict_set(&amp;options,"rtsp_transport","tcp",0);
  
      if(av_open_input_file(&amp;pFormatCtx, argv[1], NULL, 0, NULL)!=0)
  
          return -1; // Couldn't open file
  
  
  
      // Retrieve stream information
  
      if(av_find_stream_info(pFormatCtx)&lt;0)
  
          return -1; // Couldn't find stream information
  
  
  
      // Dump information about file onto standard error
  
      dump_format(pFormatCtx, 0, argv[1], false);
  
  
  
      // Find the first video stream
  
      videoStream=-1;
  
      for(i=0; inb_streams; i++)
  
          if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO)
  
          {
  
              videoStream=i;
  
              break;
  
          }
  
          if(videoStream==-1)
  
              return -1; // Didn't find a video stream
  
  
  
          // Get a pointer to the codec context for the video stream
  
          pCodecCtx=pFormatCtx->streams[videoStream]->codec;
  
  
  
          // Find the decoder for the video stream
  
          pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
  
          if(pCodec==NULL)
  
              return -1; // Codec not found
  
  
  
          // Open codec
  
          if(avcodec_open(pCodecCtx, pCodec)&lt;0)
  
              return -1; // Could not open codec
  
  
  
          // Hack to correct wrong frame rates that seem to be generated by some codecs
  
  
  
          if(pCodecCtx->time_base.num>1000 &amp;&amp; pCodecCtx->time_base.den==1)
  
              pCodecCtx->time_base.den=1000;
  
  
  
          //pCodecCtx->time_base.den=1;
  
          //pCodecCtx->time_base.num=1;
  
          // Allocate video frame
  
          pFrame=avcodec_alloc_frame();
  
  
  
          // Allocate an AVFrame structure
  
          pFrameRGB=avcodec_alloc_frame();
  
          if(pFrameRGB==NULL)
  
              return -1;
  
  
  
          // Determine required buffer size and allocate buffer
  
          numBytes=avpicture_get_size(PIX_FMT_RGB24, pCodecCtx->width,
  
              pCodecCtx->height);
  
  
  
          //buffer=malloc(numBytes);
  
          buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t));
  
  
  
          // Assign appropriate parts of buffer to image planes in pFrameRGB
  
          avpicture_fill((AVPicture *)pFrameRGB, buffer, PIX_FMT_RGB24,
  
              pCodecCtx->width, pCodecCtx->height);
  
  
  
          // Read frames and save first five frames to disk
  
          i=0;
  
          while(av_read_frame(pFormatCtx, &amp;packet)>=0)
  
          {
  
              // Is this a packet from the video stream?
  
              if(packet.stream_index==videoStream)
  
              {
  
                  // Decode video frame
  
                  avcodec_decode_video2(pCodecCtx, pFrame, &amp;frameFinished, 
  
                      &amp;packet);
  
  
  
                  // Did we get a video frame?
  
                  if(frameFinished)
  
                  {
  
  
  
                      static struct SwsContext *img_convert_ctx;
  
  
  
  #if 0
  
                      // Older removed code
  
                      // Convert the image from its native format to RGB swscale
  
                      img_convert((AVPicture *)pFrameRGB, PIX_FMT_RGB24, 
  
                          (AVPicture*)pFrame, pCodecCtx->pix_fmt, pCodecCtx->width, 
  
                          pCodecCtx->height);
  
  
  
                      // function template, for reference
  
                      int sws_scale(struct SwsContext *context, uint8_t* src[], int srcStride[], int srcSliceY,
  
                          int srcSliceH, uint8_t* dst[], int dstStride[]);
  
  #endif
  
                      // Convert the image into YUV format that SDL uses
  
                      if(img_convert_ctx == NULL) {
  
                          int w = pCodecCtx->width;
  
                          int h = pCodecCtx->height;
  
  
  
                          img_convert_ctx = sws_getContext(w, h, 
  
                              pCodecCtx->pix_fmt, 
  
                              w, h, PIX_FMT_RGB24, SWS_BICUBIC,
  
                              NULL, NULL, NULL);
  
                          if(img_convert_ctx == NULL) {
  
                              fprintf(stderr, "Cannot initialize the conversion context!\n");
  
                              exit(1);
  
                          }
  
                      }
  
                      int ret = sws_scale(img_convert_ctx, pFrame->data, pFrame->linesize, 0, 
  
                          pCodecCtx->height, pFrameRGB->data, pFrameRGB->linesize);
  
  #if 0 
  
                      // this use to be true, as of 1/2009, but apparently it is no longer true in 3/2009
  
                      if(ret) {
  
                          fprintf(stderr, "SWS_Scale failed [%d]!\n", ret);
  
                          exit(-1);
  
                      }
  
  #endif
  
  
  
                      // Save the frame to disk
  
                      if(i++&lt;=1000)
  
                          SaveFrame(pFrameRGB, pCodecCtx->width, pCodecCtx->height, i);
  
                  }
  
              }
  
  
  
              // Free the packet that was allocated by av_read_frame
  
              av_free_packet(&amp;packet);
  
              //sleep(1);
  
          }
  
  
  
          // Free the RGB image
  
          //free(buffer);
  
          av_free(buffer);
  
          av_free(pFrameRGB);
  
  
  
          // Free the YUV frame
  
          av_free(pFrame);
  
  
  
          // Close the codec
  
          avcodec_close(pCodecCtx);
  
  
  
          // Close the video file
  
          av_close_input_file(pFormatCtx);
  
  
  
          return 0;
  
  }
  
  
  
  static void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame)
  
  {
  
      FILE *pFile;
  
      char szFilename[32];
  
      int  y;
  
  
  
      // Open file
  
      sprintf(szFilename, "frame%d.ppm", iFrame);
  
      pFile=fopen(szFilename, "wb");
  
      if(pFile==NULL)
  
          return;
  
  
  
      // Write header
  
      fprintf(pFile, "P6\n%d %d\n255\n", width, height);
  
  
  
      // Write pixel data
  
      for(y=0; ydata[0]+y*pFrame->linesize[0], 1, width*3, pFile);
  
  
  
      // Close file
  
      fclose(pFile);
  
  }

• using ffmpeg to create a wavefile image from opus

  29 décembre 2015, par edwardsmarkf

  I have been trying to use ffmpeg to create a wavefile image from an opus file. so far i have found three different methods but cannot seem to determine which one is the best.

  The end result is hopefully to have a sound-wave that is only approx. 55px in height. The image will become part of a css background-image.

  Adapted from Generating a waveform using ffmpeg :

  ffmpeg -i file.opus -filter_complex
  "showwavespic,colorbalance=bs=0.5:gm=0.3:bh=-0.5,drawbox=x=(iw-w)/2:y=(ih-h)/2:w=iw:h=1:color=black@0.5"
  file.png

  which produces this image :
  

  Next, I found this one (and my favorite because of the simplicity) :

  ffmpeg -i test.opus -lavfi showwavespic=split_channels=1:s=1024x800 test.png

  And here is what that one looks like :

  

  Finally, this one from FFmpeg Wiki : Waveform, but it seems less efficient using a second utility (gnuplot) rather than just ffmpeg :

  ffmpeg -i file.opus -ac 1 -filter:a
  aresample=4000 -map 0:a -c:a pcm_s16le -f data - | \
  gnuplot -e "set
  terminal png size 525,050 ;set output
  ’file.png’ ;unset key ;unset tics ;unset border ; set
  lmargin 0 ;set rmargin 0 ;set tmargin 0 ;set bmargin 0 ; plot ’

  

  Option two is my favorite, but i dont like the margins on the top and bottom of the waveforms.

  Option three (using gnuplot) makes the best ’shaped’ image for our needs, since the initial spike in sound seems to make the rest almost too small to use (lines tend to almost disappear) when the image is sized at only 50 pixels high.

  Any suggestions how might best approach this ? I really understand very little about any of the options I see, except of course for the size. Note too i have 10’s of thousands to process, so naturally i want to make a wise choice at the very beginning.

• Embedding many small movies in page (gif vs mp4 vs webm vs ?)

  25 mars 2017, par genekogan

  I am making a webpage which will contain around 20-25 small-resolution ( 56x56) and short-length ( 3 sec) movies which will be set to autoplay and loop, so they will be looping on the page at all times. They are mostly dispersed throughout the page, so cannot easily be merged into bigger movies.

  I’m trying to decide on the right format to use, balancing filesize, quality, and processor overhead.

  mp4 seems the best option in terms of quality and filesize, however embedding many small mp4s on the page felt to me slow and made my computer get hot. Despite the fact that if they were one mp4, it would be only around 300x240 — it seems there is a lot of CPU overhead if they are divided.

  gif is lower quality and bigger filesize, but the CPU performance felt smoother. I can’t prove it though because I didn’t measure it — are gif’s known to be better performance than mp4 ?

  I have not tried other formats (webm, avi, ogg, etc) but I am unsure of how supported all of these formats are by most browsers and I want the webpage to be viewable from multiple browsers/countries.

  How can I determine the best format to use for these videos ? Is there a tool which can measure the CPU performance of my webpage so I can quantify the performance issues ?