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• ffmpeg/libx264 C API : frames dropped from end of short MP4

  19 juillet 2017, par Blake McConnell

  In my C++ application, I am taking a series of JPEG images, manipulating their data using FreeImage, and then encoding the bitmaps as H264 using the ffmpeg/libx264 C API. The output is an MP4 which shows the series of 22 images at 12fps. My code is adapted from the "muxing" example that comes with ffmpeg C source code.

  My problem : no matter how I tune the codec parameters, a certain number of frames at the end of the sequence which are passed to the encoder do not appear in the final output. I’ve set the AVCodecContext parameters like this :

  //set context params
  
  ctx->codec_id = AV_CODEC_ID_H264;
  
  ctx->bit_rate = 4000 * 1000;
  
  ctx->width = _width;
  
  ctx->height = _height;
  
  ost->st->time_base = AVRational{ 1, 12 };
  
  ctx->time_base = ost->st->time_base;
  
  ctx->gop_size = 1;
  
  ctx->pix_fmt = AV_PIX_FMT_YUV420P;

  I have found that the higher the gop_size the more frames are dropped from the end of the video. I can also see from the output that, with this gop size (where I’m essentially directing that all output frames be I frames) that only 9 frames are written.

  I’m not sure why this is occurring. I experimented with encoding duplicate frames and making a much longer video. This resulted in no frames being dropped. I know with the ffmpeg command line tool there is a concatenation command that accomplishes what I am trying to do, but I’m not sure how to accomplish the same goal using the C API.

  Here’s the output I’m getting from the console :

  [libx264 @ 026d81c0] using cpu capabilities : MMX2 SSE2Fast SSSE3
  SSE4.2 AVX FMA3 BMI2 AVX2 [libx264 @ 026d81c0] profile High, level
  3.1 [libx264 @ 026d81c0] 264 - core 152 r2851 ba24899 - H.264/MPEG-4 AVC codec - Cop yleft 2003-2017 - http://www.videolan.org/x264.html -
  options : cabac=1 ref=1 deb lock=1:0:0 analyse=0x3:0x113 me=hex subme=7
  psy=1 psy_rd=1.00:0.00 mixed_ref=0 m e_range=16 chroma_me=1 trellis=1
  8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chro ma_qp_offset=-2
  threads=12 lookahead_threads=2 sliced_threads=0 nr=0 decimate=1
  interlaced=0 bluray_compat=0 constrained_intra=0 bframes=0 weightp=0
  keyint=1 ke yint_min=1 scenecut=40 intra_refresh=0 rc=abr mbtree=0
  bitrate=4000 ratetol=1.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4
  ip_ratio=1.40 aq=1:1.00 Output #0, mp4, to
  ’....\images\c411a991-46f6-400c-8bb0-77af3738559a.mp4’ :
  Stream #0:0 : Video : h264, yuv420p, 700x700, q=2-31, 4000 kb/s, 12 tbn

  [libx264 @ 026d81c0] frame I:9 Avg QP:17.83 size:111058 [libx264
  @ 026d81c0] mb I I16..4 : 1.9% 47.7% 50.5% [libx264 @ 026d81c0] final
  ratefactor : 19.14 [libx264 @ 026d81c0] 8x8 transform intra:47.7%
  [libx264 @ 026d81c0] coded y,uvDC,uvAC intra : 98.4% 96.9% 89.5%
  [libx264 @ 026d81c0] i16 v,h,dc,p : 64% 6% 2% 28% [libx264 @
  026d81c0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu : 32% 15% 9% 5% 5% 6% 8%
  10% 10% [libx264 @ 026d81c0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu : 28% 18%
  7% 6% 8% 8% 8% 9% 8% [libx264 @ 026d81c0] i8c dc,h,v,p : 43% 22%
  25% 10% [libx264 @ 026d81c0] kb/s:10661.53

  Code included below :

  MP4Writer.h

  #ifndef MPEG_WRITER
  
  #define MPEG_WRITER
  
  
  
  #include <iostream>
  
  #include <string>
  
  #include <vector>
  
  #include 
  
  extern "C" {
  
      #include <libavformat></libavformat>avformat.h>
  
      #include <libswscale></libswscale>swscale.h>
  
      #include <libswresample></libswresample>swresample.h>
  
      #include <libswscale></libswscale>swscale.h>
  
  }
  
  
  
  typedef struct OutputStream 
  
  {
  
      AVStream *st;
  
      AVCodecContext *enc;
  
  
  
      //pts of the next frame that will be generated
  
      int64_t next_pts;
  
      int samples_count;
  
  
  
      AVFrame *frame;
  
      AVFrame *tmp_frame;
  
  
  
      float t, tincr, tincr2;
  
  
  
      struct SwsContext *sws_ctx;
  
      struct SwrContext *swr_ctx;
  
  };
  
  
  
  class MP4Writer {
  
      public:
  
          MP4Writer();
  
          void Init();
  
          int16_t SetOutput( const std::string &amp; path );
  
          int16_t AddFrame( uint8_t * imgData );
  
          int16_t Write( std::vector<imgdata> &amp; imgData );
  
          int16_t Finalize();
  
          void SetHeight( const int height ) { _height = _width = height; } //assuming 1:1 aspect ratio
  
  
  
      private:
  
          int16_t AddStream( OutputStream * ost, AVFormatContext * formatCtx, AVCodec ** codec, enum AVCodecID codecId );
  
          int16_t OpenVideo( AVFormatContext * formatCtx, AVCodec *codec, OutputStream * ost, AVDictionary * optArg );
  
          static AVFrame * AllocPicture( enum AVPixelFormat pixFmt, int width, int height );
  
          static AVFrame * GetVideoFrame( uint8_t * imgData, OutputStream * ost, const int width, const int height );
  
          static int WriteFrame( AVFormatContext * formatCtx, const AVRational * timeBase, AVStream * stream, AVPacket * packet );
  
  
  
          int _width;
  
          int _height;
  
          OutputStream _ost;
  
          AVFormatContext * _formatCtx;
  
          AVDictionary * _dict;
  
  };
  
  
  
  #endif //MPEG_WRITER
  
  </imgdata></vector></string></iostream>

  MP4Writer.cpp

  #include 
  
  #include <algorithm>
  
  
  
  MP4Writer::MP4Writer()
  
  {
  
      _width = 0;
  
      _height = 0;
  
  }
  
  
  
  void MP4Writer::Init()
  
  {
  
      av_register_all();
  
  }
  
  
  
  /**
  
   sets up output stream for the specified path.
  
   note that the output format is deduced automatically from the file extension passed
  
   @param path: output file path
  
   @returns: -1 = output could not be deduced, -2 = invalid codec, -3 = error opening output file,
  
             -4 = error writing header
  
  */
  
  int16_t MP4Writer::SetOutput( const std::string &amp; path )
  
  {
  
      int error;
  
      AVCodec * codec;
  
      AVOutputFormat * format;
  
  
  
      _ost = OutputStream{}; //TODO reset state in a more focused way?
  
  
  
      //allocate output media context
  
      avformat_alloc_output_context2( &amp;_formatCtx, NULL, NULL, path.c_str() );
  
      if ( !_formatCtx ) {
  
          std::cout &lt;&lt; "could not deduce output format from file extension.  aborting" &lt;&lt; std::endl;
  
          return -1;
  
      }
  
      //set format
  
      format = _formatCtx->oformat;
  
      if ( format->video_codec != AV_CODEC_ID_NONE ) {
  
          AddStream( &amp;_ost, _formatCtx, &amp;codec, format->video_codec );
  
      }
  
      else {
  
          std::cout &lt;&lt; "there is no video codec set.  aborting" &lt;&lt; std::endl;
  
          return -2;
  
      }
  
  
  
      OpenVideo( _formatCtx, codec, &amp;_ost, _dict );
  
  
  
      av_dump_format( _formatCtx, 0, path.c_str(), 1 );
  
  
  
      //open output file
  
      if ( !( format->flags &amp; AVFMT_NOFILE )) {
  
          error = avio_open( &amp;_formatCtx->pb, path.c_str(), AVIO_FLAG_WRITE );
  
          if ( error &lt; 0 ) {
  
              std::cout &lt;&lt; "there was an error opening output file " &lt;&lt; path &lt;&lt; ".  aborting" &lt;&lt; std::endl;
  
              return -3;
  
          }
  
      }
  
  
  
      //write header
  
      error = avformat_write_header( _formatCtx, &amp;_dict );
  
      if ( error &lt; 0 ) {
  
          std::cout &lt;&lt; "an error occurred writing header. aborting" &lt;&lt; std::endl;
  
          return -4;
  
      }
  
  
  
      return 0;
  
  }
  
  
  
  /**
  
   initialize the output stream
  
   @param ost: the output stream
  
   @param formatCtx: the context format
  
   @param codec: the output codec
  
   @param codec: the ffmpeg enumerated id of the codec
  
   @returns: -1 = encoder not found, -2 = stream could not be allocated, -3 = encoding context could not be allocated
  
  */
  
  int16_t MP4Writer::AddStream( OutputStream * ost, AVFormatContext * formatCtx, AVCodec ** codec, enum AVCodecID codecId )
  
  {
  
      AVCodecContext * ctx; //TODO not sure why this is here, could just set ost->enc directly
  
      int i;
  
  
  
      //detect the encoder
  
      *codec = avcodec_find_encoder( codecId );
  
      if ( (*codec) == NULL ) {
  
          std::cout &lt;&lt; "could not find encoder.  aborting" &lt;&lt; std::endl;
  
          return -1;
  
      }
  
  
  
      //allocate stream
  
      ost->st = avformat_new_stream( formatCtx, NULL );
  
      if ( ost->st == NULL ) {
  
          std::cout &lt;&lt; "could not allocate stream.  aborting" &lt;&lt; std::endl;
  
          return -2;
  
      }
  
  
  
      //allocate encoding context
  
      ost->st->id = formatCtx->nb_streams - 1;
  
      ctx = avcodec_alloc_context3( *codec );
  
      if ( ctx == NULL ) {
  
          std::cout &lt;&lt; "could not allocate encoding context.  aborting" &lt;&lt; std::endl;
  
          return -3;
  
      }
  
  
  
      ost->enc = ctx;
  
  
  
      //set context params
  
      ctx->codec_id = AV_CODEC_ID_H264;
  
      ctx->bit_rate = 4000 * 1000;
  
      ctx->width = _width;
  
      ctx->height = _height;
  
      ost->st->time_base = AVRational{ 1, 12 };
  
      ctx->time_base = ost->st->time_base;
  
      ctx->gop_size = 1;
  
      ctx->pix_fmt = AV_PIX_FMT_YUV420P;
  
  
  
      //if neccesary, set stream headers and formats separately
  
      if ( formatCtx->oformat->flags &amp; AVFMT_GLOBALHEADER ) {
  
          std::cout &lt;&lt; "setting stream and headers to be separate" &lt;&lt; std::endl;
  
          ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
  
      }
  
  
  
      return 0;
  
  }
  
  
  
  /**
  
   open the video for writing
  
   @param formatCtx: the format context
  
   @param codec: output codec
  
   @param ost: output stream
  
   @param optArg: dictionary
  
   @return: -1 = error opening codec, -2 = allocate new frame, -3 = copy stream params
  
  */
  
  int16_t MP4Writer::OpenVideo( AVFormatContext * formatCtx, AVCodec *codec, OutputStream * ost, AVDictionary * optArg )
  
  {
  
      int error;
  
      AVCodecContext * ctx = ost->enc;
  
      AVDictionary * dict = NULL;
  
      av_dict_copy( &amp;dict, optArg, 0 );
  
  
  
      //open codec
  
      error = avcodec_open2( ctx, codec, &amp;dict );
  
      av_dict_free( &amp;dict );
  
      if ( error &lt; 0 ) {
  
          std::cout &lt;&lt; "there was an error opening the codec.  aborting" &lt;&lt; std::endl;
  
          return -1;
  
      }
  
  
  
      //allocate new frame
  
      ost->frame = AllocPicture( ctx->pix_fmt, ctx->width, ctx->height );
  
      if ( ost->frame == NULL ) {
  
          std::cout &lt;&lt; "there was an error allocating a new frame.  aborting" &lt;&lt; std::endl;
  
          return -2;
  
      }
  
  
  
      //copy steam params
  
      error = avcodec_parameters_from_context( ost->st->codecpar, ctx );
  
      if ( error &lt; 0 ) {
  
          std::cout &lt;&lt; "could not copy stream parameters.  aborting" &lt;&lt; std::endl;
  
          return -3;
  
      }
  
  
  
      return 0;
  
  }
  
  
  
  /**
  
   allocate a new frame
  
   @param pixFmt: ffmpeg enumerated pixel format
  
   @param width: output width
  
   @param height: output height
  
   @returns: an inititalized frame
  
  */
  
  AVFrame * MP4Writer::AllocPicture( enum AVPixelFormat pixFmt, int width, int height )
  
  {
  
      AVFrame * picture;
  
      int error;
  
  
  
      //allocate the frame
  
      picture = av_frame_alloc();
  
      if ( picture == NULL ) {
  
          std::cout &lt;&lt; "there was an error allocating the picture" &lt;&lt; std::endl;
  
          return NULL;
  
      }
  
  
  
      picture->format = pixFmt;
  
      picture->width = width;
  
      picture->height = height;
  
  
  
      //allocate the frame's data buffer
  
      error = av_frame_get_buffer( picture, 32 );
  
      if ( error &lt; 0 ) {
  
          std::cout &lt;&lt; "could not allocate frame data" &lt;&lt; std::endl;
  
          return NULL;
  
      }
  
      picture->pts = 0;
  
      return picture;
  
  }
  
  
  
  /**
  
   convert raw RGB buffer to YUV frame
  
   @return: frame that contains image data
  
  */
  
  AVFrame * MP4Writer::GetVideoFrame( uint8_t * imgData, OutputStream * ost, const int width, const int height )
  
  {
  
      int error;
  
      AVCodecContext * ctx = ost->enc;
  
  
  
      //prepare the frame
  
      error = av_frame_make_writable( ost->frame );
  
      if ( error &lt; 0 ) {
  
          std::cout &lt;&lt; "could not make frame writeable" &lt;&lt; std::endl;
  
          return NULL;
  
      }
  
  
  
      //TODO set this context one time per run, or even better, one time at init
  
      //convert RGB to YUV
  
      struct SwsContext* fooContext = sws_getContext( width, height, AV_PIX_FMT_BGR24, 
  
          width, height, AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL );
  
      int inLinesize[1] = { 3 * width }; // RGB stride
  
      uint8_t * inData[1] = { imgData };
  
      int sliceHeight = sws_scale( fooContext, inData, inLinesize, 0, height, ost->frame->data, ost->frame->linesize );
  
      sws_freeContext( fooContext );
  
  
  
      ost->frame->pts = ost->next_pts++;
  
      //TODO does the frame need to be returned here as it is available at the class level?
  
      return ost->frame;
  
  }
  
  
  
  /**
  
   write frame to file
  
   @param formatCtx: the output format context
  
   @param timeBase: the framerate
  
   @param stream: output stream
  
   @param packet: data packet
  
   @returns: see return values for av_interleaved_write_frame
  
  */
  
  int MP4Writer::WriteFrame( AVFormatContext * formatCtx, const AVRational * timeBase, AVStream * stream, AVPacket * packet )
  
  {
  
      av_packet_rescale_ts( packet, *timeBase, stream->time_base );
  
      packet->stream_index = stream->index;
  
  
  
      //write compressed file to media file
  
      return av_interleaved_write_frame( formatCtx, packet );
  
  }
  
  
  
  int16_t MP4Writer::Write( std::vector<imgdata> &amp; imgData )
  
  {
  
      int16_t errorCount = 0;
  
      int16_t retVal = 0;
  
      bool countingUp = true;
  
      size_t i = 0;
  
      while ( true ) {
  
          //don't show first frame again when counting back down
  
          if ( !countingUp &amp;&amp; i == 0 ) {
  
              break;
  
          }
  
          uint8_t * pixels = imgData[i].GetBits( imgData[i].mp4Input );
  
          AddFrame( pixels );
  
  
  
          //handle inc/dec without repeating last frame
  
          if ( countingUp ) {
  
              if ( i == imgData.size() -1 ) {
  
                  countingUp = false;
  
                  i--;
  
              }
  
              else {
  
                  i++;
  
              }
  
          }
  
          else {
  
              i--;
  
          }
  
      }
  
      Finalize();
  
      return 0; //TODO return error code
  
  }
  
  
  
  /**
  
   add another frame to output video
  
   @param imgData: the raw image data
  
   @returns -1 = error encoding video frame, -2 = error writing frame
  
  */
  
  int16_t MP4Writer::AddFrame( uint8_t * imgData )
  
  {
  
      int error;
  
      AVCodecContext * ctx;
  
      AVFrame * frame;
  
      int gotPacket = 0;
  
      AVPacket pkt = { 0 };
  
  
  
      ctx = _ost.enc;
  
      av_init_packet( &amp;pkt );
  
  
  
      frame = GetVideoFrame( imgData, &amp;_ost, _width, _height );
  
  
  
      //encode the image
  
      error = avcodec_encode_video2( ctx, &amp;pkt, frame, &amp;gotPacket );
  
      if ( error &lt; 0 ) {
  
          std::cout &lt;&lt; "there was an error encoding the video frame" &lt;&lt; std::endl;
  
          return -1;
  
      }
  
  
  
      //write the frame.  NOTE: this doesn't kick in until the encoder has received a certain number of frames
  
      if ( gotPacket ) {
  
          error = WriteFrame( _formatCtx, &amp;ctx->time_base, _ost.st, &amp;pkt );
  
          if ( error &lt; 0 ) {
  
              std::cout &lt;&lt; "the video frame could not be written" &lt;&lt; std::endl;
  
              return -2;
  
          }
  
      }
  
      return 0;
  
  }
  
  
  
  /**
  
   finalize output video and cleanup
  
  */
  
  int16_t MP4Writer::Finalize()
  
  {
  
      av_write_trailer( _formatCtx );
  
      avcodec_free_context( &amp;_ost.enc );
  
      av_frame_free( &amp;_ost.frame);
  
      av_frame_free( &amp;_ost.tmp_frame );
  
      avio_closep( &amp;_formatCtx->pb );
  
      avformat_free_context( _formatCtx );
  
      sws_freeContext( _ost.sws_ctx );
  
      swr_free( &amp;_ost.swr_ctx);
  
      return 0;
  
  }
  
  </imgdata></algorithm>

  usage

  #include 
  
  #include 
  
  #include <vector>
  
  
  
  struct ImgData
  
  {
  
      unsigned int width;
  
      unsigned int height;
  
      std::string path;
  
      FIBITMAP * mp4Input;
  
  
  
      uint8_t * GetBits( FIBITMAP * bmp ) { return FreeImage_GetBits( bmp ); }
  
  };
  
  
  
  int main()
  
  {
  
       std::vector<imgdata> imgDataVec;
  
       //load images and push to imgDataVec
  
       MP4Writer mp4Writer;
  
       mp4Writer.SetHeight( 1200 ); //assumes 1:1 aspect ratio
  
       mp4Writer.Init();
  
       mp4Writer.SetOutput( "test.mp4" );
  
       mp4Writer.Write( imgDataVec );
  
  }
  
  </imgdata></vector>

• configure : Don’t explicitly disable PIC for windows targets

  28 mai 2013, par Martin Storsjö

  configure : Don’t explicitly disable PIC for windows targets
  This reverts e08c946c6 and 05165c2f7a. The actual intention of
  
  e08c946c6 was to fix shared library builds for arm/win32, which
  
  can also be accomplished in other ways.
  Disabling pic on those platforms broke inline assembly on cygwin/64
  
  (since some inline assembly requires knowing whether we are building
  
  as PIC or not), and might also break inline assembly on other
  
  compilers on windows.
  As a side-effect, this unfortunately brings back all the warnings
  
  about PIC not having any effect on that platform.
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DH] configure

• FFMPEG Muxing from Audio and Video files.(C++)

  27 mai 2013, par Michael IV

  I am learning how to create MP4 video from this example.The problem is that the example demonstrates audio encoding from some dummy source data generated on the fly.I need to encode audio from a file.I have checked many examples and most of them show the same or just a separate audio encoding.
  In my trial and error process I am using the same AVFormatContext for both audio and video frames.I am not sure if it's right thing to do, or should I rather have 2 separate contexts ?So far I got Video encoding ok but audio stream fails as AVPacket can't locate correct audio stream index.
  Here is how I setup audio stream :

    void open_audio(AVFormatContext *oc, AVCodec **codec, AVStream **st ,enum AVCodecID codec_id){
  
  
  
      //    AVCodecContext *c;
  
      int ret;
  
      //    c = st->codec;
  
  
  
      *codec = avcodec_find_encoder(codec_id);
  
      if (!(*codec)) {
  
          fprintf(stderr, "Could not find encoder for '%s'\n",avcodec_get_name(codec_id));
  
  
  
      }
  
      /* open it */
  
  
  
  
  
  
  
      if(avformat_open_input(&oc,_audioInName.c_str(),NULL,NULL) !=0){
  
  
  
          Msg::PrintErrorMsg("Error opening audio file");
  
  
  
      }
  
  
  
  
  
      AVStream* audioStream = NULL;
  
  
  
      // Find the audio stream (some container files can have multiple streams in them)
  
  
  
      for (uint32_t i = 0; i < oc->nb_streams; ++i)
  
  
  
      {
  
  
  
          if (oc->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO)
  
  
  
          {
  
  
  
              audioStream = oc->streams[i];
  
  
  
              break;
  
  
  
          }
  
  
  
      }
  
  
  
      if (audioStream == NULL)
  
      {
  
          Msg::PrintErrorMsg("Could not find any audio stream in the file");
  
  
  
      }
  
      *st =audioStream;
  
  
  
      AVCodecContext *c  = audioStream->codec;
  
      c->codec = *codec;//avcodec_find_decoder(c->codec_id);
  
      audioStream->id = 1;
  
      c->sample_fmt  = AV_SAMPLE_FMT_S16;
  
      c->bit_rate    = 64000;
  
      c->sample_rate = 44100;
  
      c->channels    = 1;
  
  
  
      if (oc->oformat->flags & AVFMT_GLOBALHEADER){
  
          c->flags |= CODEC_FLAG_GLOBAL_HEADER;
  
  
  
      }
  
  
  
      if (c->codec == NULL)
  
      {
  
          Msg::PrintErrorMsg("Couldn't find a proper decoder");
  
  
  
      }
  
  
  
      ret = avcodec_open2(c, *codec, NULL);
  
      if (ret < 0) {
  
  
  
          Msg::PrintErrorMsg("Could not open audio codec\n");
  
  
  
      }
  
  
  
  }

  Here "oc" is the same context used to initialize video stream as well.

  Then I am trying to write audio frame like this :

    void write_audio_frame(AVFormatContext *oc, AVStream *st){
  
      AVCodecContext *c;
  
      AVPacket pkt = { 0 }; // data and size must be 0;
  
      AVFrame *frame = avcodec_alloc_frame();
  
      int got_packet, ret;
  
      av_init_packet(&pkt);
  
      c = st->codec;
  
      /////
  
      //  get_audio_frame(samples, audio_input_frame_size, c->channels);
  
  
  
      ////Read the packet:
  
      while(av_read_frame(oc,&pkt) == 0 ){
  
  
  
          if(pkt.stream_index ==st->index){
  
  
  
          // Try to decode the packet into a frame
  
          int frameFinished = 0;
  
          avcodec_decode_audio4(c, frame, &frameFinished, &pkt);
  
  
  
          // Some frames rely on multiple packets, so we have to make sure the frame is finished before
  
          // we can use it
  
          if (frameFinished){
  
              assert(frameFinished);
  
              ret = avcodec_encode_audio2(c, &pkt, frame, &got_packet);
  
              if (ret < 0) {
  
                  Msg::PrintErrorMsg("Error encoding audio frame\n");
  
  
  
              }
  
              if (!got_packet){
  
                  printf("failed to aquire packet");
  
              }
  
              pkt.stream_index = st->index;
  
              /* Write the compressed frame to the media file. */
  
              ret = av_interleaved_write_frame(oc, &pkt);
  
              if (ret != 0) {
  
  
  
                  Msg::PrintErrorMsg("Error while writing audio frame.");
  
              }
  
  
  
            }
  
          }
  
  
  
         }
  
      }
  
      av_free_packet(&pkt);
  
      avcodec_free_frame(&frame);
  
  }

  The thing is I never pass this statement : "if(pkt.stream_index ==st->index)".Packet stream index is never equal to the audio stream index.Anyone can point out where I am wrong ?