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• vcodec copy does not work when start/duration is messed up in video file

  25 janvier 2014, par anishsane

  My Video file shows below meta-data with ffprobe/ffmpeg :

  Duration: 00:44:27.52, start: 1333.760000, bitrate: 335 kb/s
  
    Stream #0.0(und): Video: h264 (Main), yuv420p, 640x480, 25 tbr, 90k tbn, 50 tbc

  Note : The file does not contain audio.

  I am trying to convert this video file to other video file, using ffmpeg/avconv.

  This works : (but encodes h.264 video to mpeg4)

  ffmpeg -i input.mp4 output.mp4

  & it generates output file of proper duration (44:27 - 1333 seconds = 22:14)

  This does not work :

  ffmpeg -i input.mp4 -vcodec copy output.mp4

  Generates file without video.

  The output contains :

  $ avconv -i input.mp4 -vcodec copy output.mp4
  
  
  
  avconv version 0.8.9-6:0.8.9-0ubuntu0.13.10.1, Copyright (c) 2000-2013 the Libav developers
  
    built on Nov  9 2013 19:09:46 with gcc 4.8.1
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'input.mp4':
  
    Metadata:
  
      major_brand     : dash
  
      minor_version   : 0
  
      compatible_brands: iso6avc1mp41
  
      creation_time   : 2014-01-19 22:43:21
  
    Duration: 00:44:27.52, start: 1333.760000, bitrate: 335 kb/s
  
      Stream #0.0(und): Video: h264 (Main), yuv420p, 640x480, 25 tbr, 90k tbn, 50 tbc
  
      Metadata:
  
        creation_time   : 2014-01-19 22:43:21
  
  Output #0, mp4, to 'output.mp4':
  
    Metadata:
  
      major_brand     : dash
  
      minor_version   : 0
  
      compatible_brands: iso6avc1mp41
  
      creation_time   : 2014-01-19 22:43:21
  
      encoder         : Lavf53.21.1
  
      Stream #0.0(und): Video: ![0][0][0] / 0x0021, yuv420p, 640x480, q=2-31, 90k tbn, 90k tbc
  
      Metadata:
  
        creation_time   : 2014-01-19 22:43:21
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (copy)
  
  Press ctrl-c to stop encoding
  
  frame=    0 fps=  0 q=-1.0 Lsize=       0kB time=10000000000.00 bitrate=   0.0kbits/s    
  
  video:0kB audio:0kB global headers:0kB muxing overhead inf%

• Visualizing Call Graphs Using Gephi

  1er septembre 2014, par Multimedia Mike — General

  When I was at university studying computer science, I took a basic chemistry course. During an accompanying lab, the teaching assistant chatted me up and asked about my major. He then said, “Computer science ? Well, that’s just typing stuff, right ?”

  My impulsive retort : “Sure, and chemistry is just about mixing together liquids and coming up with different colored liquids, as seen on the cover of my high school chemistry textbook, right ?”

  
  
  

  In fact, pure computer science has precious little to do with typing (as is joked in CS circles, computer science is about computers in the same way that astronomy is about telescopes). However, people who study computer science often pursue careers as programmers, or to put it in fancier professional language, software engineers.

  So, what’s a software engineer’s job ? Isn’t it just typing ? That’s where I’ve been going with this overly long setup. After thinking about it for long enough, I like to say that a software engineer’s trade is managing complexity.

  A few years ago, I discovered Gephi, an open source tool for graph and data visualization. It looked neat but I didn’t have much use for it at the time. Recently, however, I was trying to get a better handle on a large codebase. I.e., I was trying to manage the project’s complexity. And then I thought of Gephi again.

  Prior Work
  One way to get a grip on a large C codebase is to instrument it for profiling and extract details from the profiler. On Linux systems, this means compiling and linking the code using the -pg flag. After running the executable, there will be a gmon.out file which is post-processed using the gprof command.

  GNU software development tools have a reputation for being rather powerful and flexible, but also extremely raw. This first hit home when I was learning how to use the GNU tool for code coverage — gcov — and the way it outputs very raw data that you need to massage with other tools in order to get really useful intelligence.

  And so it is with gprof output. The output gives you a list of functions sorted by the amount of processing time spent in each. Then it gives you a flattened call tree. This is arranged as “during the profiled executions, function c was called by functions a and b and called functions d, e, and f ; function d was called by function c and called functions g and h”.

  How can this call tree data be represented in a more instructive manner that is easier to navigate ? My first impulse (and I don’t think I’m alone in this) is to convert the gprof call tree into a representation suitable for interpretation by Graphviz. Unfortunately, doing so tends to generate some enormous and unwieldy static images.

  Feeding gprof Data To Gephi
  I learned of Gephi a few years ago and recalled it when I developed an interest in gaining better perspective on a large base of alien C code. To understand what this codebase is doing for a particular use case, instrument it with gprof, gather execution data, and then study the code paths.

  How could I feed the gprof data into Gephi ? Gephi supports numerous graphing formats including an XML-based format named GEXF.

  Thus, the challenge becomes converting gprof output to GEXF.

  Which I did.

  Demonstration
  I have been absent from FFmpeg development for a long time, which is a pity because a lot of interesting development has occurred over the last 2-3 years after a troubling period of stagnation. I know that 2 big video codec developments have been HEVC (next in the line of MPEG codecs) and VP9 (heir to VP8’s throne). FFmpeg implements them both now.

  I decided I wanted to study the code flow of VP9. So I got the latest FFmpeg code from git and built it using the options "--extra-cflags=-pg --extra-ldflags=-pg". Annoyingly, I also needed to specify "--disable-asm" because gcc complains of some register allocation snafus when compiling inline ASM in profiling mode (and this is on x86_64). No matter ; ASM isn’t necessary for understanding overall code flow.

  After compiling, the binary ‘ffmpeg_g’ will have symbols and be instrumented for profiling. I grabbed a sample from this VP9 test vector set and went to work.

  ./ffmpeg_g -i vp90-2-00-quantizer-00.webm -f null /dev/null
  gprof ./ffmpeg_g > vp9decode.txt
  convert-gprof-to-gexf.py vp9decode.txt > /bigdisk/vp9decode.gexf
  

  Gephi loads vp9decode.gexf with no problem. Using Gephi, however, can be a bit challenging if one is not versed in any data exploration jargon. I recommend this Gephi getting starting guide in slide deck form. Here’s what the default graph looks like :

  
  
  

  Not very pretty or helpful. BTW, that beefy arrow running from mid-top to lower-right is the call from decode_coeffs_b -> iwht_iwht_4x4_add_c. There were 18774 from the former to the latter in this execution. Right now, the edge thicknesses correlate to number of calls between the nodes, which I’m not sure is the best representation.

  Following the tutorial slide deck, I at least learned how to enable the node labels (function symbols in this case) and apply a layout algorithm. The tutorial shows the force atlas layout. Here’s what the node neighborhood looks like for probing file type :

  
  
  

  Okay, so that’s not especially surprising– avprobe_input_format3 calls all of the *_probe functions in order to automatically determine input type. Let’s find that decode_coeffs_b function and see what its neighborhood looks like :

  
  
  

  That’s not very useful. Perhaps another algorithm might help. I select the Fruchterman–Reingold algorithm instead and get a slightly more coherent representation of the decoding node neighborhood :

  
  
  

  Further Work
  Obviously, I’m just getting started with this data exploration topic. One thing I would really appreciate in such a tool is the ability to interactively travel the graph since that’s what I’m really hoping to get out of this experiment– watching the code flows.

  Perhaps someone else can find better use cases for visualizing call graph data. Thus, I have published the source code for this tool at Github.

• libavcodec : how to encode with h264 codec ,with mp4 container using controllable frame rate and bitrate(through c code)

  26 mai 2016, par musimbate

  I am trying to record the screen of a pc and encode the recorded frames using h264 encoder
  and wrap them into a mp4 container.I want to do this because this super user link http://superuser.com/questions/300897/what-is-a-codec-e-g-divx-and-how-does-it-differ-from-a-file-format-e-g-mp/300997#300997 suggests it allows good trade-off between size and quality of the output file.

  The application I am working on should allow users to record a few hours of video and have the minimum output file size with decent quality.

  The code I have cooked up so far allows me to record and save .mpg(container) files with the mpeg1video encoder

  Running :

  ffmpeg -i test.mpg

  on the output file gives the following output :

   [mpegvideo @ 028c7400] Estimating duration from bitrate, this may be inaccurate
  
  Input #0, mpegvideo, from 'test.mpg':
  
    Duration: 00:00:00.29, bitrate: 104857 kb/s
  
      Stream #0:0: Video: mpeg1video, yuv420p(tv), 1366x768 [SAR 1:1 DAR 683:384], 104857 kb/s, 25 fps, 25 tbr, 1200k tbn, 25 tbc

  I have these settings for my output :

   const char * filename="test.mpg";
  
      int codec_id= AV_CODEC_ID_MPEG1VIDEO;
  
      AVCodec *codec11;
  
      AVCodecContext *outContext= NULL;
  
      int got_output;
  
      FILE *f;
  
      AVPacket pkt;
  
      uint8_t endcode[] = { 0, 0, 1, 0xb7 };
  
  
  
      /* put sample parameters */
  
      outContext->bit_rate = 400000;
  
      /* resolution must be a multiple of two */
  
      outContext->width=pCodecCtx->width;
  
      outContext->height=pCodecCtx->height;
  
      /* frames per second */
  
      outContext->time_base.num=1;
  
      outContext->time_base.den=25;
  
      /* emit one intra frame every ten frames
  
       * check frame pict_type before passing frame
  
       * to encoder, if frame->pict_type is AV_PICTURE_TYPE_I
  
       * then gop_size is ignored and the output of encoder
  
       * will always be I frame irrespective to gop_size
  
       */
  
      outContext->gop_size = 10;
  
      outContext->max_b_frames = 1;
  
      outContext->pix_fmt = AV_PIX_FMT_YUV420P;

  When I change int codec_id= AV_CODEC_ID_MPEG1VIDEO to int codec_id= AV_CODEC_ID_H264 i get a file that does not play with vlc.

  I have read that writing the

  uint8_t endcode[] = { 0, 0, 1, 0xb7 };

  array at the end of your file when finished encoding makes your file a legitimate mpeg file.It is written like this :

   fwrite(endcode, 1, sizeof(endcode), f);
  
      fclose(f);

  in my code. Should I do the same thing when I change my encoder to AV_CODEC_ID_H264 ?

  I am capturing using gdi input like this :

  AVDictionary* options = NULL;
  
      //Set some options
  
      //grabbing frame rate
  
      av_dict_set(&options,"framerate","30",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;
  
          }

  I want to be able to modify my grabbing rate to optimize for the outptut file size
  but When I change it to 20 for example I get a video that plays so fast.How do
  I get a video that plays with normal speed with frames captured at 20 fps or any
  lower frame rate value ?

  While recording I get the following output on the standard error output :

  [gdigrab @ 00cdb8e0] Capturing whole desktop as 1366x768x32 at (0,0)
  
  Input #0, gdigrab, from '(null)':
  
    Duration: N/A, start: 1420718663.655713, bitrate: 1006131 kb/s
  
      Stream #0:0: Video: bmp, bgra, 1366x768, 1006131 kb/s, 29.97 tbr, 1000k tbn, 29.97 tbc
  
  [swscaler @ 00d24120] Warning: data is not aligned! This can lead to a speedloss
  
  [mpeg1video @ 00cdd160] AVFrame.format is not set
  
  [mpeg1video @ 00cdd160] AVFrame.width or height is not set
  
  [mpeg1video @ 00cdd160] AVFrame.format is not set
  
  [mpeg1video @ 00cdd160] AVFrame.width or height is not set
  
  [mpeg1video @ 00cdd160] AVFrame.format is not set

  How do I get rid of this error in my code ?

  In summary :
  1) How do I encode h264 video wrapped into mp4 container ?

  2) How do I capture at lower frame rates and still play
  the encoded video at normal speed ?

  3) How do I set the format(and which format—depends on the codec ?)
  and width and height info on the frames I write ?

  The code I am using in its entirety is shown below

  extern "C"
  
  {
  
  #include "libavcodec/avcodec.h"
  
  #include "libavformat/avformat.h"
  
  #include "libswscale/swscale.h"
  
  #include "libavdevice/avdevice.h"
  
  
  
  
  
  #include <libavutil></libavutil>opt.h>
  
  #include <libavutil></libavutil>channel_layout.h>
  
  #include <libavutil></libavutil>common.h>
  
  #include <libavutil></libavutil>imgutils.h>
  
  #include <libavutil></libavutil>mathematics.h>
  
  #include <libavutil></libavutil>samplefmt.h>
  
  //SDL
  
  #include "SDL.h"
  
  #include "SDL_thread.h"
  
  }
  
  
  
  //Output YUV420P
  
  #define OUTPUT_YUV420P 0
  
  //'1' Use Dshow
  
  //'0' Use GDIgrab
  
  #define USE_DSHOW 0
  
  
  
  int main(int argc, char* argv[])
  
  {
  
  
  
      //1.WE HAVE THE FORMAT CONTEXT
  
      //THIS IS FROM THE DESKTOP GRAB STREAM.
  
      AVFormatContext *pFormatCtx;
  
      int             i, videoindex;
  
      AVCodecContext  *pCodecCtx;
  
      AVCodec         *pCodec;
  
  
  
      av_register_all();
  
      avformat_network_init();
  
  
  
      //ASSIGN STH TO THE FORMAT CONTEXT.
  
      pFormatCtx = avformat_alloc_context();
  
  
  
      //Register Device
  
      avdevice_register_all();
  
      //Windows
  
  #ifdef _WIN32
  
  #if USE_DSHOW
  
      //Use dshow
  
      //
  
      //Need to Install screen-capture-recorder
  
      //screen-capture-recorder
  
      //Website: http://sourceforge.net/projects/screencapturer/
  
      //
  
      AVInputFormat *ifmt=av_find_input_format("dshow");
  
      //if(avformat_open_input(&amp;pFormatCtx,"video=screen-capture-recorder",ifmt,NULL)!=0){
  
      if(avformat_open_input(&amp;pFormatCtx,"video=UScreenCapture",ifmt,NULL)!=0){
  
          printf("Couldn't open input stream.\n");
  
          return -1;
  
      }
  
  #else
  
      //Use gdigrab
  
      AVDictionary* options = NULL;
  
      //Set some options
  
      //grabbing frame rate
  
      av_dict_set(&amp;options,"framerate","30",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;
  
      }
  
  
  
  #endif
  
  #endif//FOR THE WIN32 THING.
  
  
  
      if(avformat_find_stream_info(pFormatCtx,NULL)&lt;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)&lt;0)
  
      {
  
          printf("Could not open codec.\n");
  
          return -1;
  
      }
  
  
  
      //THIS IS WHERE YOU CONTROL THE FORMAT(THROUGH FRAMES).
  
      AVFrame *pFrame;
  
  
  
      pFrame=av_frame_alloc();
  
  
  
      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");
  
  
  
  
  
  //&lt;&lt;--FOR WRITING MPG FILES
  
      //&lt;&lt;--START:PREPARE TO WRITE YOUR MPG FILE.
  
  
  
      const char * filename="test.mpg";
  
      int codec_id= AV_CODEC_ID_MPEG1VIDEO;
  
  
  
  
  
  
  
      AVCodec *codec11;
  
      AVCodecContext *outContext= NULL;
  
      int got_output;
  
      FILE *f;
  
      AVPacket pkt;
  
      uint8_t endcode[] = { 0, 0, 1, 0xb7 };
  
  
  
      printf("Encode video file %s\n", filename);
  
  
  
      /* find the mpeg1 video encoder */
  
      codec11 = avcodec_find_encoder((AVCodecID)codec_id);
  
      if (!codec11) {
  
          fprintf(stderr, "Codec not found\n");
  
          exit(1);
  
      }
  
  
  
      outContext = avcodec_alloc_context3(codec11);
  
      if (!outContext) {
  
          fprintf(stderr, "Could not allocate video codec context\n");
  
          exit(1);
  
      }
  
  
  
      /* put sample parameters */
  
      outContext->bit_rate = 400000;
  
      /* resolution must be a multiple of two */
  
  
  
      outContext->width=pCodecCtx->width;
  
      outContext->height=pCodecCtx->height;
  
  
  
  
  
      /* frames per second */
  
      outContext->time_base.num=1;
  
      outContext->time_base.den=25;
  
  
  
      /* emit one intra frame every ten frames
  
       * check frame pict_type before passing frame
  
       * to encoder, if frame->pict_type is AV_PICTURE_TYPE_I
  
       * then gop_size is ignored and the output of encoder
  
       * will always be I frame irrespective to gop_size
  
       */
  
      outContext->gop_size = 10;
  
      outContext->max_b_frames = 1;
  
      outContext->pix_fmt = AV_PIX_FMT_YUV420P;
  
  
  
      if (codec_id == AV_CODEC_ID_H264)
  
          av_opt_set(outContext->priv_data, "preset", "slow", 0);
  
  
  
      /* open it */
  
      if (avcodec_open2(outContext, codec11, NULL) &lt; 0) {
  
          fprintf(stderr, "Could not open codec\n");
  
          exit(1);
  
      }
  
  
  
      f = fopen(filename, "wb");
  
      if (!f) {
  
          fprintf(stderr, "Could not open %s\n", filename);
  
          exit(1);
  
      }
  
  
  
  
  
      AVFrame *outframe = av_frame_alloc();
  
      int nbytes = avpicture_get_size(outContext->pix_fmt,
  
                                     outContext->width,
  
                                     outContext->height);
  
  
  
      uint8_t* outbuffer = (uint8_t*)av_malloc(nbytes);
  
  
  
     //ASSOCIATE THE FRAME TO THE ALLOCATED BUFFER.
  
      avpicture_fill((AVPicture*)outframe, outbuffer,
  
                     AV_PIX_FMT_YUV420P,
  
                     outContext->width, outContext->height);
  
  
  
      SwsContext* swsCtx_ ;
  
      swsCtx_= sws_getContext(pCodecCtx->width,
  
                              pCodecCtx->height,
  
                              pCodecCtx->pix_fmt,
  
                              outContext->width, outContext->height,
  
                              outContext->pix_fmt,
  
                              SWS_BICUBIC, NULL, NULL, NULL);
  
  
  
  
  
      //HERE WE START PULLING PACKETS FROM THE SPECIFIED FORMAT CONTEXT.
  
      while(av_read_frame(pFormatCtx, packet)>=0)
  
      {
  
          if(packet->stream_index==videoindex)
  
          {
  
              ret= avcodec_decode_video2(pCodecCtx,
  
                                           pFrame,
  
                                           &amp;got_picture,packet );
  
              if(ret &lt; 0)
  
              {
  
                  printf("Decode Error.\n");
  
                  return -1;
  
              }
  
              if(got_picture)
  
              {
  
  
  
              sws_scale(swsCtx_, pFrame->data, pFrame->linesize,
  
                    0, pCodecCtx->height, outframe->data,
  
                    outframe->linesize);
  
  
  
  
  
              av_init_packet(&amp;pkt);
  
              pkt.data = NULL;    // packet data will be allocated by the encoder
  
              pkt.size = 0;
  
  
  
  
  
              ret = avcodec_encode_video2(outContext, &amp;pkt, outframe, &amp;got_output);
  
              if (ret &lt; 0) {
  
                 fprintf(stderr, "Error encoding frame\n");
  
                 exit(1);
  
                }
  
  
  
              if (got_output) {
  
                  printf("Write frame %3d (size=%5d)\n", i, pkt.size);
  
                  fwrite(pkt.data, 1, pkt.size, f);
  
                  av_free_packet(&amp;pkt);
  
                 }
  
  
  
              }
  
          }
  
  
  
          av_free_packet(packet);
  
      }//THE LOOP TO PULL PACKETS FROM THE FORMAT CONTEXT ENDS HERE.
  
  
  
  
  
  
  
      //
  
      /* get the delayed frames */
  
      for (got_output = 1; got_output; i++) {
  
          //fflush(stdout);
  
  
  
          ret = avcodec_encode_video2(outContext, &amp;pkt, NULL, &amp;got_output);
  
          if (ret &lt; 0) {
  
              fprintf(stderr, "Error encoding frame\n");
  
              exit(1);
  
          }
  
  
  
          if (got_output) {
  
              printf("Write frame %3d (size=%5d)\n", i, pkt.size);
  
              fwrite(pkt.data, 1, pkt.size, f);
  
              av_free_packet(&amp;pkt);
  
          }
  
      }
  
  
  
  
  
  
  
      /* add sequence end code to have a real mpeg file */
  
      fwrite(endcode, 1, sizeof(endcode), f);
  
      fclose(f);
  
  
  
      avcodec_close(outContext);
  
      av_free(outContext);
  
      //av_freep(&amp;frame->data[0]);
  
      //av_frame_free(&amp;frame);
  
  
  
      //THIS WAS ADDED LATER
  
      av_free(outbuffer);
  
  
  
      avcodec_close(pCodecCtx);
  
      avformat_close_input(&amp;pFormatCtx);
  
  
  
      return 0;
  
  }

  Thank you for your time.