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• how to reduce output size while capturing webcam video using ffmpeg ?

  27 novembre 2014, par Chris Snow

  I am capturing output from my webcam as follows :

  ffmpeg -y -an -vcodec rawvideo -f video4linux2 -s 320x240 -i /dev/video0 out.mpg

  I would like to trade off quality of the output in order to reduce the amount of data that is recorded but I don’t know what options to set.

  Any pointers will be appreciated - video encoding is a completely new area and unknown area of computer science for me.

• ffmpeg record screen and save video file to disk as .mp4 or .mpg

  5 janvier 2015, par musimbate

  I want to record the screen of my pc (using gdigrab on my windows machine) and store the saved video file on my disk as an mp4 or mpg file .I have found an example piece of code that grabs the screen and shows it in an SDL window here :http://xwk.iteye.com/blog/2125720 (The code is on the bottom of the page and has an english version) and the ffmpeg muxing example https://ffmpeg.org/doxygen/trunk/muxing_8c-source.html seems to be able to help encode audio and video into a desired output video file.

  I have tried to combine these two by having a format context for grabbing the screen (AVFormatContext *pFormatCtx ; in my code ) and a separate format context to write the desired video file (AVFormatContext *outFormatContextEncoded ;).Within the loop to read packets from the input stream( screen grab stream) I directly encode write packets to the output file as shown in my code.I have kept the SDL code so I can see what I am recording.Below is my code with my modified write_video_frame() function .

  The code builds OK but the output video can’t be played by vlc. When I run the command

  ffmpeg -i filename.mpg

  I get this output

  [mpeg @ 003fed20] probed stream 0 failed
  
  [mpeg @ 003fed20] Stream #0: not enough frames to estimate rate; consider increasing probesize
  
  [mpeg @ 003fed20] Could not find codec parameters for stream 0 (Video: none): unknown codec
  
  Consider increasing the value for the 'analyzeduration' and 'probesize' options
  
  karamage.mpg: could not find codec parameters
  
  Input #0, mpeg, from 'karamage.mpg':
  
    Duration: 19:30:09.25, start: 37545.438756, bitrate: 2 kb/s
  
      Stream #0:0[0x1e0]: Video: none, 90k tbr, 90k tbn
  
  At least one output file must be specified

  Am I doing something wrong here ? I am new to ffmpeg and any guidance on this is highly appreciated.Thank you for your time.

  int main(int argc, char* argv[])
  
  {
  
  
  
      AVFormatContext *pFormatCtx;
  
  
  
      int             i, videoindex;
  
      AVCodecContext  *pCodecCtx;
  
      AVCodec         *pCodec;
  
  
  
      av_register_all();
  
      avformat_network_init();
  
  
  
      //Localy defined structure.
  
      OutputStream outVideoStream = { 0 };
  
  
  
      const char *filename;
  
      AVOutputFormat *outFormatEncoded;
  
      AVFormatContext *outFormatContextEncoded;
  
      AVCodec *videoCodec;
  
  
  
      filename="karamage.mpg";
  
  
  
      int ret1;
  
  
  
      int have_video = 0, have_audio = 0;
  
      int encode_video = 0, encode_audio = 0;
  
  
  
  
  
      AVDictionary *opt = NULL;
  
  
  
  
  
  
  
      //ASSIGN STH TO THE FORMAT CONTEXT.
  
      pFormatCtx = avformat_alloc_context();
  
  
  
      //
  
      //Use this when opening a local file.
  
      //char filepath[]="src01_480x272_22.h265";
  
      //avformat_open_input(&pFormatCtx,filepath,NULL,NULL)
  
  
  
      //Register Device
  
      avdevice_register_all();
  
  
  
      //Use gdigrab
  
      AVDictionary* options = NULL;
  
      //Set some options
  
      //grabbing frame rate
  
      //av_dict_set(&options,"framerate","5",0);
  
      //The distance from the left edge of the screen or desktop
  
      //av_dict_set(&options,"offset_x","20",0);
  
      //The distance from the top edge of the screen or desktop
  
      //av_dict_set(&options,"offset_y","40",0);
  
      //Video frame size. The default is to capture the full screen
  
      //av_dict_set(&options,"video_size","640x480",0);
  
      AVInputFormat *ifmt=av_find_input_format("gdigrab");
  
      if(avformat_open_input(&pFormatCtx,"desktop",ifmt,&options)!=0){
  
          printf("Couldn't open input stream.\n");
  
          return -1;
  
      }
  
  
  
      if(avformat_find_stream_info(pFormatCtx,NULL)<0)
  
      {
  
          printf("Couldn't find stream information.\n");
  
          return -1;
  
      }
  
      videoindex=-1;
  
      for(i=0; inb_streams; i++) 
  
          if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO)
  
          {
  
              videoindex=i;
  
              break;
  
          }
  
      if(videoindex==-1)
  
      {
  
          printf("Didn't find a video stream.\n");
  
          return -1;
  
      }
  
      pCodecCtx=pFormatCtx->streams[videoindex]->codec;
  
      pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
  
      if(pCodec==NULL)
  
      {
  
          printf("Codec not found.\n");
  
          return -1;
  
      }
  
      if(avcodec_open2(pCodecCtx, pCodec,NULL)<0)
  
      {
  
          printf("Could not open codec.\n");
  
          return -1;
  
      }
  
  
  
  
  
      AVFrame *pFrame,*pFrameYUV;
  
      pFrame=avcodec_alloc_frame();
  
      pFrameYUV=avcodec_alloc_frame();
  
  
  
      //PIX_FMT_YUV420P WHAT DOES THIS SAY ABOUT THE FORMAT??
  
      uint8_t *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);
  
  
  
      //<<<<<<<<<<<-------PREP WORK TO WRITE ENCODED VIDEO FILES-----
  
  
  
      avformat_alloc_output_context2(&outFormatContextEncoded, NULL, NULL, filename);
  
      if (!outFormatContextEncoded) {
  
          printf("Could not deduce output format from file extension: using MPEG.\n");
  
          avformat_alloc_output_context2(&outFormatContextEncoded, NULL, "mpeg", filename);
  
      }
  
      if (!outFormatContextEncoded)
  
          return 1;
  
  
  
      outFormatEncoded=outFormatContextEncoded->oformat;
  
  
  
  
  
       //THIS CREATES THE STREAMS(AUDIO AND VIDEO) ADDED TO OUR OUTPUT STREAM
  
  
  
      if (outFormatEncoded->video_codec != AV_CODEC_ID_NONE) {
  
  
  
          //YOUR VIDEO AND AUDIO PROPS ARE SET HERE.
  
          add_stream(&outVideoStream, outFormatContextEncoded, &videoCodec, outFormatEncoded->video_codec);
  
          have_video = 1;
  
          encode_video = 1;
  
      }
  
  
  
  
  
       // Now that all the parameters are set, we can open the audio and
  
       // video codecs and allocate the necessary encode buffers. 
  
      if (have_video)
  
          open_video(outFormatContextEncoded, videoCodec, &outVideoStream, opt);
  
  
  
       av_dump_format(outFormatContextEncoded, 0, filename, 1);
  
  
  
  
  
        /* open the output file, if needed */
  
      if (!(outFormatEncoded->flags & AVFMT_NOFILE)) {
  
          ret1 = avio_open(&outFormatContextEncoded->pb, filename, AVIO_FLAG_WRITE);
  
          if (ret1 < 0) {
  
              //fprintf(stderr, "Could not open '%s': %s\n", filename,
  
              //        av_err2str(ret));
  
              fprintf(stderr, "Could not open your dumb file.\n");
  
              return 1;
  
          }
  
      }
  
  
  
  
  
      /* Write the stream header, if any. */
  
      ret1 = avformat_write_header(outFormatContextEncoded, &opt);
  
      if (ret1 < 0) {
  
          //fprintf(stderr, "Error occurred when opening output file: %s\n",
  
           //       av_err2str(ret));
  
          fprintf(stderr, "Error occurred when opening output file\n");
  
          return 1;
  
      }
  
  
  
  
  
      //<<<<<<<<<<<-------PREP WORK TO WRITE ENCODED VIDEO FILES-----
  
  
  
      //SDL----------------------------
  
      if(SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {  
  
          printf( "Could not initialize SDL - %s\n", SDL_GetError()); 
  
          return -1;
  
      } 
  
      int screen_w=640,screen_h=360;
  
      const SDL_VideoInfo *vi = SDL_GetVideoInfo();
  
      //Half of the Desktop's width and height.
  
      screen_w = vi->current_w/2;
  
      screen_h = vi->current_h/2;
  
      SDL_Surface *screen; 
  
      screen = SDL_SetVideoMode(screen_w, screen_h, 0,0);
  
  
  
      if(!screen) {  
  
          printf("SDL: could not set video mode - exiting:%s\n",SDL_GetError());  
  
          return -1;
  
      }
  
      SDL_Overlay *bmp; 
  
      bmp = SDL_CreateYUVOverlay(pCodecCtx->width, pCodecCtx->height,SDL_YV12_OVERLAY, screen); 
  
      SDL_Rect rect;
  
      //SDL End------------------------
  
      int ret, got_picture;
  
  
  
      AVPacket *packet=(AVPacket *)av_malloc(sizeof(AVPacket));
  
  
  
      //TRY TO INIT THE PACKET HERE
  
       av_init_packet(packet);
  
  
  
  
  
      //Output Information-----------------------------
  
      printf("File Information---------------------\n");
  
      av_dump_format(pFormatCtx,0,NULL,0);
  
      printf("-------------------------------------------------\n");
  
  
  
      struct SwsContext *img_convert_ctx;
  
      img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL); 
  
      //------------------------------
  
      //
  
      while(av_read_frame(pFormatCtx, packet)>=0)
  
      {
  
  
  
          if(packet->stream_index==videoindex)
  
          {
  
              //HERE WE DECODE THE PACKET INTO THE FRAME
  
              ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, packet);
  
              if(ret < 0)
  
              {
  
                  printf("Decode Error.\n");
  
                  return -1;
  
              }
  
              if(got_picture)
  
              {
  
  
  
                  //THIS IS WHERE WE DO STH WITH THE FRAME WE JUST GOT FROM THE STREAM
  
                  //FREE AREA--START
  
                  //IN HERE YOU CAN WORK WITH THE FRAME OF THE PACKET.
  
                  write_video_frame(outFormatContextEncoded, &outVideoStream,packet);
  
  
  
  
  
                  //FREE AREA--END
  
                  sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameYUV->data, pFrameYUV->linesize);
  
  
  
  
  
                  SDL_LockYUVOverlay(bmp);
  
                  bmp->pixels[0]=pFrameYUV->data[0];
  
                  bmp->pixels[2]=pFrameYUV->data[1];
  
                  bmp->pixels[1]=pFrameYUV->data[2];     
  
                  bmp->pitches[0]=pFrameYUV->linesize[0];
  
                  bmp->pitches[2]=pFrameYUV->linesize[1];   
  
                  bmp->pitches[1]=pFrameYUV->linesize[2];
  
                  SDL_UnlockYUVOverlay(bmp); 
  
                  rect.x = 0;    
  
                  rect.y = 0;    
  
                  rect.w = screen_w;    
  
                  rect.h = screen_h;  
  
                  SDL_DisplayYUVOverlay(bmp, &rect); 
  
                  //Delay 40ms----WHY THIS DELAY????
  
                  SDL_Delay(40);
  
              }
  
          }
  
          av_free_packet(packet);
  
      }//THE LOOP TO PULL PACKETS FROM THE FORMAT CONTEXT ENDS HERE.
  
  
  
      //AFTER THE WHILE LOOP WE DO SOME CLEANING
  
  
  
      //av_read_pause(context);
  
  
  
  
  
       av_write_trailer(outFormatContextEncoded);
  
       close_stream(outFormatContextEncoded, &outVideoStream);
  
       if (!(outFormatContextEncoded->flags & AVFMT_NOFILE))
  
          /* Close the output file. */
  
          avio_close(outFormatContextEncoded->pb);
  
  
  
      /* free the stream */
  
      avformat_free_context(outFormatContextEncoded);
  
  
  
  
  
  
  
      //STOP DOING YOUR CLEANING
  
      sws_freeContext(img_convert_ctx);
  
  
  
  
  
  
  
      SDL_Quit();
  
  
  
      av_free(out_buffer);
  
      av_free(pFrameYUV);
  
      avcodec_close(pCodecCtx);
  
      avformat_close_input(&pFormatCtx);
  
  
  
      return 0;
  
  }
  
  
  
  
  
  
  
  /*
  
   * encode one video frame and send it to the muxer
  
   * return 1 when encoding is finished, 0 otherwise
  
   */
  
  static int write_video_frame(AVFormatContext *oc, OutputStream *ost,AVPacket * pkt11)
  
  {
  
      int ret;
  
      AVCodecContext *c;
  
      AVFrame *frame;
  
      int got_packet = 0;
  
  
  
      c = ost->st->codec;
  
  
  
      //DO NOT NEED THIS FRAME.
  
      //frame = get_video_frame(ost);
  
  
  
      if (oc->oformat->flags & AVFMT_RAWPICTURE) {
  
  
  
          //IGNORE THIS FOR A MOMENT
  
          /* a hack to avoid data copy with some raw video muxers */
  
          AVPacket pkt;
  
          av_init_packet(&pkt);
  
  
  
          if (!frame)
  
              return 1;
  
  
  
          pkt.flags        |= AV_PKT_FLAG_KEY;
  
          pkt.stream_index  = ost->st->index;
  
          pkt.data          = (uint8_t *)frame;
  
          pkt.size          = sizeof(AVPicture);
  
  
  
          pkt.pts = pkt.dts = frame->pts;
  
          av_packet_rescale_ts(&pkt, c->time_base, ost->st->time_base);
  
  
  
          ret = av_interleaved_write_frame(oc, &pkt);
  
      } else {
  
  
  
              ret = write_frame(oc, &c->time_base, ost->st, pkt11);
  
  
  
      }
  
  
  
      if (ret < 0) {
  
          fprintf(stderr, "Error while writing video frame: %s\n");
  
          exit(1);
  
      }
  
  
  
  
  
      return 1;
  
  }

• Saving scatterplot animations with matplotlib produces blank video file

  1er avril 2013, par user2175850

  I am having a very similar problem to this question

  but the suggested solution doesn't work for me.

  I have set up an animated scatter plot using the matplotlib animation module. This works fine when it is displaying live. I would like to save it to an avi file or something similar. The code I have written to do this does not error out but the video it produces just shows a blank set of axes or a black screen. I've done several checks and the data is being run and figure updated it's just not getting saved to video...

  I tried removing "animated=True" and "blit=True" as suggested in this question but that did not fix the problem.

  I have placed the relevant code below but can provide more if necessary. Could anyone suggest what I should do to get this working ?

  def initAnimation(self):
  
          rs, cfgs = next(self.jumpingDataStreamIterator)     
  
          #self.scat = self.axAnimation.scatter(rs[0], rs[1], c=cfgs[0], marker='o')
  
          self.scat = self.axAnimation.scatter(rs[0], rs[1], c=cfgs[0], marker='o', animated=True)
  
          return self.scat,
  
  
  
  
  
  def updateAnimation(self, i):
  
      """Update the scatter plot."""
  
      rs, cfgs = next(self.jumpingDataStreamIterator)
  
      # Set x and y data...
  
      self.scat.set_offsets(rs[:2,].transpose()) 
  
      #self.scat = self.axAnimation.scatter(rs[0], rs[1], c=cfgs[0], animated=True)
  
      # Set sizes...
  
      #self.scat._sizes = 300 * abs(data[2])**1.5 + 100
  
      # Set colors..
  
      #self.scat.set_array(cfgs[0])
  
      # We need to return the updated artist for FuncAnimation to draw..
  
      # Note that it expects a sequence of artists, thus the trailing comma.
  
      matplotlib.pyplot.draw()
  
      return self.scat,
  
  
  
  def animate2d(self, steps=None, showEvery=50, size = 25):
  
      self.figAnimation, self.axAnimation = matplotlib.pyplot.subplots()
  
      self.axAnimation.set_aspect("equal")
  
      self.axAnimation.axis([-size, size, -size, size])
  
      self.jumpingDataStreamIterator = self.jumpingDataStream(showEvery)
  
  
  
      self.univeseAnimation = matplotlib.animation.FuncAnimation(self.figAnimation, 
  
                              self.updateAnimation, init_func=self.initAnimation,
  
                              blit=True)
  
      matplotlib.pyplot.show()
  
  
  
  def animate2dVideo(self,fileName=None, steps=10000, showEvery=50, size=25):
  
      self.figAnimation, self.axAnimation = matplotlib.pyplot.subplots()
  
      self.axAnimation.set_aspect("equal")
  
      self.axAnimation.axis([-size, size, -size, size])
  
      self.Writer = matplotlib.animation.writers['ffmpeg']
  
      self.writer = self.Writer(fps=1, metadata=dict(artist='Universe Simulation'))
  
      self.jumpingDataStreamIterator = self.jumpingDataStream(showEvery)
  
  
  
      self.universeAnimation = matplotlib.animation.FuncAnimation(self.figAnimation, 
  
                              self.updateAnimation, scipy.arange(1, 25), init_func=self.initAnimation)
  
  
  
      self.universeAnimation.save('C:/universeAnimation.mp4', writer = self.writer)