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• avformat_find_stream_info not return on Linux

  23 novembre 2015, par yuan tian

  I want to fetch the camera video stream on both windows and linux.The code goes everything well with windows.But when I transplant it to Linux,function avformat_find_stream_info can Not return !

  bool VideoFetcher::enumCamera(){
  
  for (int i = 0; i<10; i++){
  
      AVInputFormat *pInputFormat = av_find_input_format(
  
          #ifdef __WIN32
  
                  "dshow"
  
          #elif __linux
  
                  "v4l2"
  
          #else
  
                  ""
  
          #endif
  
                  );
  
      assert(pInputFormat);
  
  #ifdef __linux
  
      char str[128];
  
      sprintf(str, "/dev/video%d", i);
  
  #endif
  
      AVDictionary* dictionary = NULL;
  
      //av_dict_set(&dictionary, "video_size", "640x480", NULL);
  
      //av_dict_set(&dictionary, "framerate", "30", NULL);
  
      if (avformat_open_input(
  
                  &this->cameraFormatContext,
  
          #ifdef __WIN32
  
                  (std::string("video=")+thg-¬>getCameraName()).c_str(),
  
          #elif __linux
  
                  str,
  
          #else
  
           ""
  
          #endif
  
                  pInputFormat, &dictionary)
  
              < 0)
  
              {
  
  
  
                      Log("Error : Couldn't open the camera\n");
  
              }else{
  
                      return true;
  
              }
  
      }
  
      return false;
  
   }
  
  assert(avFormatContext);
  
  // int streamError;
  
  auto streamError = avformat_find_stream_info(avFormatContext, NULL);
  
  //the function can not return !
  
  printf("findcodec1\n");
  
  if (streamError< 0){
  
          throw StreamErrorException();
  
   }

• DirectShowLib library is not working with .MP4

  4 novembre 2015, par Ragesh Puthiyedath

  I am a newbie in using DirectShowLib for create image thumbnails from video.

  Now i try to use this library for make a thumbnail of my .mp4 video.

  Please see my code below.

  public static bool CreateThumb(string videoFilename, string thumbFilename, double positionPercent)
  
      {
  
          //Logger.ReportInfo("Creating thumb for " + videoFilename);
  
          bool rval = false;
  
          try
  
          {
  
  
  
              IMediaDet m = new MediaDet() as IMediaDet;
  
              m.put_Filename(videoFilename);
  
  
  
              int streamCount;
  
              m.get_OutputStreams(out streamCount);
  
  
  
              AMMediaType media_type = new AMMediaType();
  
  
  
              for (int i = 0; i < streamCount; i++)
  
              {
  
                  m.get_StreamMediaType(media_type);
  
  
  
                  VideoInfoHeader vih = (VideoInfoHeader)Marshal.PtrToStructure(media_type.formatPtr, typeof(VideoInfoHeader));
  
  
  
                  if (vih == null)
  
                  {
  
                      continue;
  
                  }
  
  
  
                  double pos;
  
                  m.get_StreamLength(out pos);
  
                  pos = (int)(pos * positionPercent);
  
  
  
                  int width = vih.BmiHeader.Width;
  
                  int height = vih.BmiHeader.Height;
  
  
  
                  if (height < 10 || width < 10)
  
                  {
  
                      continue;
  
                  }
  
  
  
                  string tempfile = Path.GetTempFileName() + ".bmp";
  
  
  
                  m.WriteBitmapBits(pos, width, height, tempfile);
  
  
  
                  if (File.Exists(tempfile))
  
                  {
  
                      using (var bitmap = new Bitmap(tempfile))
  
                      {
  
                          bitmap.Save(thumbFilename, ImageFormat.Png);
  
                      }
  
  
  
                      File.Delete(tempfile);
  
                      rval = true;
  
                  }
  
  
  
                  break;
  
              }
  
  
  
              Marshal.ReleaseComObject(m);
  
  
  
          }
  
          catch (Exception ex)
  
          {
  
  
  
              throw ex;
  
          }
  
          return rval;
  
  
  
      }

  But this method is skiped after this line code execution.

  m.get_OutputStreams(out streamCount) ;

  streamCount is always ’0’. Is this library is not supported the .mp4 format.

  Please give me a advice.

  Thanks

• FFmpeg muxing to avi

  2 septembre 2015, par Uncia

  sI have program, that succefully shows h264 stream using SDL : I’m getting h264 frame, decode it using ffmpeg and draw using SDL.
  Also I can write frames to file (using fwrite) and play this file through ffplay.

  But I want to mux data to the avi and face some problems in av_write_frame.

  Here is my code :

  ...
  
  /*Initializing format context - outFormatContext is the member of my class*/
  
  AVOutputFormat *outFormat;
  
  outFormat = av_guess_format(NULL,"out.avi",NULL);
  
  outFormat->video_codec = AV_CODEC_ID_H264;
  
  outFormat->audio_codec = AV_CODEC_ID_NONE;
  
  avformat_alloc_output_context2(&outFormatContext, outFormat, NULL, "out.avi");
  
  AVCodec *outCodec;
  
  AVStream *outStream = add_stream(outFormatContext, &outCodec, outFormatContext->oformat->video_codec);
  
  avcodec_open2(outStream->codec, outCodec, NULL);
  
  av_dump_format(outFormatContext, 0, "out.avi", 1);
  
  if (avio_open(&outFormatContext->pb, "out.avi", AVIO_FLAG_WRITE) < 0) 
  
      throw Exception("Couldn't open file");
  
  if (avformat_write_header(outFormatContext, NULL) < 0)
  
      throw Exception("Couldn't write to file");
  
   //I don't have exceptions here - so there is 6KB header in out.avi.
  
   ...
  
  
  
  static AVStream *add_stream(AVFormatContext *oc, AVCodec **codec,
  
                          enum AVCodecID codec_id)
  
  {
  
  AVCodecContext *c;
  
  AVStream *st;
  
  /* find the encoder */
  
  *codec = avcodec_find_encoder(codec_id);
  
  if (!(*codec)) 
  
      throw("Could not find encoder");
  
  st = avformat_new_stream(oc, *codec);
  
  if (!st) 
  
      throw ("Could not allocate stream");
  
  st->id = oc->nb_streams-1;
  
  c = st->codec;
  
  c->bit_rate = 400000;
  
  /* Resolution must be a multiple of two. */
  
  c->width    = 1920;
  
  c->height   = 1080;
  
  c->pix_fmt  = PIX_FMT_YUV420P;
  
  c->flags = 0;
  
  c->time_base.num = 1;
  
  c->time_base.den = 25;
  
  c->gop_size      = 12; /* emit one intra frame every twelve frames at most */
  
  return st;
  
  }
  
  ...
  
  /* Part of decoding loop. There is AVPacket packet - h264 packet;
  
  int ret = av_write_frame(outFormatContext, &packet); //it return -22 code - Invadlid argument;
  
  if (avcodec_decode_video2(pCodecCtx, pFrame, &frameDecoded, &packet) < 0) 
  
      return;
  
  if (frameDecoded)
  
  {
  
     //SDL stuff
  
  }

  Also i tried to use avcodec_encode_video2 (encode pFrame back to the H264) next to the SDL stuff but encoding is not working - i’ve got empty packets :( It is the second problem.

  Using av_interleaved_write_frame causes acces violation.

  Code of the muxing part i copied from ffmpeg muxing example (https://www.ffmpeg.org/doxygen/2.1/doc_2examples_2muxing_8c-example.html)