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• How to save data of packet.data using ffmpeg && c language ?

  12 juin 2015, par patrick

  I’m try to build an app in c that extract audio from video and save it as audio file. I’m able to extract the audio but now the problem is how to save it. I wrote the code given below but it’s giving me an segmentation fault. Thanks in advance.

  My code is :

  AVOutputFormat* fmt = av_guess_format("mp3", NULL, NULL);;
  
  AVFormatContext* oc = avformat_alloc_context();
  
  oc->oformat = fmt;
  
  avio_open2(&oc->pb, "test.mp3", AVIO_FLAG_WRITE,NULL,NULL);
  
  
  
  AVStream* stream=NULL;
  
  int cnt = 0;
  
  
  
  while(av_read_frame(pFormatCtx, &packet)>=0) { //pFormatCtx is input file format context.
  
      if (packet.stream_index==audioStream) {
  
      int got_frame = 0;
  
      if (avcodec_decode_audio4(pCodecCtx, pFrame, &got_frame, &packet) < 0) {
  
          fprintf(stderr, "Error encoding frame\n");
  
                  exit(1);
  
          }
  
  
  
          if(got_frame) {
  
          if (av_interleaved_write_frame(oc, &packet) < 0) {
  
                  printf(stderr, "Error writing frame\n");
  
                      exit(1);
  
                  }
  
          }
  
      }
  
      av_free_packet(&packet);
  
      av_init_packet(&packet);
  
  }

• How to convert natural language to structural description like FFmpeg filter graph strings

  11 juillet 2022, par 张无敌

  I'm working on a program that takes natural language as input, and outputs valid FFmpeg filter graph description, for example :

  


  Input string :

  


  rotate 1.mp4 90deg clockwise, downscale to 480p, output 2.mpeg


  


  Output description :

  


  rotate=a=90,scale=640*480


  


  It seems impractical with complete natural language, especially in the case of complex filter graphs, but still doable with slightly formatted input.

  


  I am new to NLP, wondering which areas or methods could help implement this.

  


• How to save data of packet.data in ffmpeg using c language ?

  10 juin 2015, par patrick

  I’m try to build an app in c that extract audio from video and save it as audio file. I write the below code. I’m able to extract the audio but now the problem is how to save it. Thanks in advance.

  My code is :

  int main(int argc, char *argv[]) {
  
  AVFormatContext *pFormatCtx = NULL;
  
  int             i;
  
  AVCodecContext  *pCodecCtx = NULL;
  
  AVCodec         *pCodec = NULL;
  
  AVFrame         *pFrame = NULL; 
  
  AVPacket        packet;
  
  
  
  AVDictionary    *optionsDict = NULL;
  
  
  
  if(argc < 2) {
  
  printf("Please provide a movie file\n");
  
  return -1;
  
  }
  
  av_register_all();
  
  if(avformat_open_input(&pFormatCtx, argv[1], NULL, NULL)!=0)
  
  return -1; 
  
  
  
  if(avformat_find_stream_info(pFormatCtx, NULL)<0)
  
  return -1; 
  
  
  
  av_dump_format(pFormatCtx, 0, argv[1], 0);
  
  
  
  int audioStream=-1;
  
  for(i=0; inb_streams; i++)
  
      if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_AUDIO) {
  
          audioStream=i;
  
          break;
  
      }
  
  if(audioStream==-1)
  
  return -1; 
  
  
  
  pCodecCtx=pFormatCtx->streams[audioStream]->codec;
  
  
  
  pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
  
  if(pCodec==NULL) {
  
      fprintf(stderr, "Unsupported codec!\n");
  
      return -1; // Codec not found
  
  }
  
  
  
  if(avcodec_open2(pCodecCtx, pCodec, &optionsDict)<0)
  
  return -1; 
  
  
  
  pFrame=avcodec_alloc_frame();
  
  packet.data = NULL;
  
  packet.size = 0;
  
  
  
  while(av_read_frame(pFormatCtx, &packet)>=0) {
  
      int got_frame = 0;
  
      int ret = avcodec_decode_audio4(pCodecCtx, pFrame, &got_frame, &packet);
  
      if(got_frame && packet.stream_index==audioStream) {
  
          //save result but how???
  
      }
  
      av_free_packet(&packet);
  
  }
  
  av_free(pFrame);
  
  avcodec_close(pCodecCtx);
  
  avformat_close_input(&pFormatCtx);
  
  return 0;
  
  }