title: ffmpeg record screen and save video file to disk as .mpg
body: <p>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 :<a href="http://xwk.iteye.com/blog/2125720" rel="nofollow">http://xwk.iteye.com/blog/2125720</a>  (The code is on the bottom of the page and has an english version)  and the ffmpeg muxing example <a href="https://ffmpeg.org/doxygen/trunk/muxing_8c-source.html" rel="nofollow">https://ffmpeg.org/doxygen/trunk/muxing_8c-source.html</a>  seems to be able to help encode audio and video into a desired output video file.</p>
  
  <p>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 .</p>
  
  <p>The code builds OK but the output video can't be played by vlc. When I run the command</p>
  
  <pre><code>ffmpeg -i filename.mpg
  </code></pre>
  
  <p>I get this output</p>
  
  <pre><code>[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
  </code></pre>
  
  <p>Am I doing something wrong here? I am new to ffmpeg and any guidance on this is highly appreciated.Thank you for your time.</p>
  
  <pre><code>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(&amp;pFormatCtx,filepath,NULL,NULL)
  
      //Register Device
      avdevice_register_all();
  
      //Use gdigrab
      AVDictionary* options = NULL;
      //Set some options
      //grabbing frame rate
      //av_dict_set(&amp;options,"framerate","5",0);
      //The distance from the left edge of the screen or desktop
      //av_dict_set(&amp;options,"offset_x","20",0);
      //The distance from the top edge of the screen or desktop
      //av_dict_set(&amp;options,"offset_y","40",0);
      //Video frame size. The default is to capture the full screen
      //av_dict_set(&amp;options,"video_size","640x480",0);
      AVInputFormat *ifmt=av_find_input_format("gdigrab");
      if(avformat_open_input(&amp;pFormatCtx,"desktop",ifmt,&amp;options)!=0){
          printf("Couldn't open input stream.\n");
          return -1;
      }
  
      if(avformat_find_stream_info(pFormatCtx,NULL)&lt;0)
      {
          printf("Couldn't find stream information.\n");
          return -1;
      }
      videoindex=-1;
      for(i=0; i&lt;pFormatCtx-&gt;nb_streams; i++) 
          if(pFormatCtx-&gt;streams[i]-&gt;codec-&gt;codec_type==AVMEDIA_TYPE_VIDEO)
          {
              videoindex=i;
              break;
          }
      if(videoindex==-1)
      {
          printf("Didn't find a video stream.\n");
          return -1;
      }
      pCodecCtx=pFormatCtx-&gt;streams[videoindex]-&gt;codec;
      pCodec=avcodec_find_decoder(pCodecCtx-&gt;codec_id);
      if(pCodec==NULL)
      {
          printf("Codec not found.\n");
          return -1;
      }
      if(avcodec_open2(pCodecCtx, pCodec,NULL)&lt;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-&gt;width, pCodecCtx-&gt;height));
  
  
      avpicture_fill((AVPicture *)pFrameYUV, out_buffer, PIX_FMT_YUV420P, pCodecCtx-&gt;width, pCodecCtx-&gt;height);
  
      //&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;-------PREP WORK TO WRITE ENCODED VIDEO FILES-----
  
      avformat_alloc_output_context2(&amp;outFormatContextEncoded, NULL, NULL, filename);
      if (!outFormatContextEncoded) {
          printf("Could not deduce output format from file extension: using MPEG.\n");
          avformat_alloc_output_context2(&amp;outFormatContextEncoded, NULL, "mpeg", filename);
      }
      if (!outFormatContextEncoded)
          return 1;
  
      outFormatEncoded=outFormatContextEncoded-&gt;oformat;
  
  
       //THIS CREATES THE STREAMS(AUDIO AND VIDEO) ADDED TO OUR OUTPUT STREAM
  
      if (outFormatEncoded-&gt;video_codec != AV_CODEC_ID_NONE) {
  
          //YOUR VIDEO AND AUDIO PROPS ARE SET HERE.
          add_stream(&amp;outVideoStream, outFormatContextEncoded, &amp;videoCodec, outFormatEncoded-&gt;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, &amp;outVideoStream, opt);
  
       av_dump_format(outFormatContextEncoded, 0, filename, 1);
  
  
        /* open the output file, if needed */
      if (!(outFormatEncoded-&gt;flags &amp; AVFMT_NOFILE)) {
          ret1 = avio_open(&amp;outFormatContextEncoded-&gt;pb, filename, AVIO_FLAG_WRITE);
          if (ret1 &lt; 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, &amp;opt);
      if (ret1 &lt; 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;
      }
  
  
      //&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;-------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-&gt;current_w/2;
      screen_h = vi-&gt;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-&gt;width, pCodecCtx-&gt;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-&gt;width, pCodecCtx-&gt;height, pCodecCtx-&gt;pix_fmt, pCodecCtx-&gt;width, pCodecCtx-&gt;height, PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL); 
      //------------------------------
      //
      while(av_read_frame(pFormatCtx, packet)&gt;=0)
      {
  
          if(packet-&gt;stream_index==videoindex)
          {
              //HERE WE DECODE THE PACKET INTO THE FRAME
              ret = avcodec_decode_video2(pCodecCtx, pFrame, &amp;got_picture, packet);
              if(ret &lt; 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, &amp;outVideoStream,packet);
  
  
                  //FREE AREA--END
                  sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame-&gt;data, pFrame-&gt;linesize, 0, pCodecCtx-&gt;height, pFrameYUV-&gt;data, pFrameYUV-&gt;linesize);
  
  
                  SDL_LockYUVOverlay(bmp);
                  bmp-&gt;pixels[0]=pFrameYUV-&gt;data[0];
                  bmp-&gt;pixels[2]=pFrameYUV-&gt;data[1];
                  bmp-&gt;pixels[1]=pFrameYUV-&gt;data[2];     
                  bmp-&gt;pitches[0]=pFrameYUV-&gt;linesize[0];
                  bmp-&gt;pitches[2]=pFrameYUV-&gt;linesize[1];   
                  bmp-&gt;pitches[1]=pFrameYUV-&gt;linesize[2];
                  SDL_UnlockYUVOverlay(bmp); 
                  rect.x = 0;    
                  rect.y = 0;    
                  rect.w = screen_w;    
                  rect.h = screen_h;  
                  SDL_DisplayYUVOverlay(bmp, &amp;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, &amp;outVideoStream);
       if (!(outFormatContextEncoded-&gt;flags &amp; AVFMT_NOFILE))
          /* Close the output file. */
          avio_close(outFormatContextEncoded-&gt;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(&amp;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-&gt;st-&gt;codec;
  
      //DO NOT NEED THIS FRAME.
      //frame = get_video_frame(ost);
  
      if (oc-&gt;oformat-&gt;flags &amp; AVFMT_RAWPICTURE) {
  
          //IGNORE THIS FOR A MOMENT
          /* a hack to avoid data copy with some raw video muxers */
          AVPacket pkt;
          av_init_packet(&amp;pkt);
  
          if (!frame)
              return 1;
  
          pkt.flags        |= AV_PKT_FLAG_KEY;
          pkt.stream_index  = ost-&gt;st-&gt;index;
          pkt.data          = (uint8_t *)frame;
          pkt.size          = sizeof(AVPicture);
  
          pkt.pts = pkt.dts = frame-&gt;pts;
          av_packet_rescale_ts(&amp;pkt, c-&gt;time_base, ost-&gt;st-&gt;time_base);
  
          ret = av_interleaved_write_frame(oc, &amp;pkt);
      } else {
  
              ret = write_frame(oc, &amp;c-&gt;time_base, ost-&gt;st, pkt11);
  
      }
  
      if (ret &lt; 0) {
          fprintf(stderr, "Error while writing video frame: %s\n");
          exit(1);
      }
  
  
      return 1;
  }
  </code></pre>