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• libx264 encoded video lags by few seconds in comparison to audio

  18 septembre 2017, par Herdesh Verma

  Below is the code i am using for reading a .3gp file encoding it using libx264 and writing it to .mp4 container. Code is working but when i play .mp4 file then video is not in sync with audio. Video is few second slow in comparison to audio.

  // Read all packet from context
  
  while( av_read_frame( fmt_ctx , pAVPacket ) >= 0 )
  
  {
  
      int decoded = pAVPacket->size;
  
      if(pAVPacket->stream_index == video_stream_idx)
  
      {
  
          //decode packet
  
          value = avcodec_decode_video2(video_dec_ctx , pAVFrame , 
  
          &frameFinished , pAVPacket );
  
          if( value < 0)
  
          {
  
              av_free_packet(pAVPacket);
  
              return -1;
  
          }
  
  
  
          if(frameFinished)// Frame successfully decoded :)
  
          {
  
              sws_scale(swsCtx_, (const uint8_t *const *) pAVFrame->data, 
  
              pAVFrame->linesize, 0, video_dec_ctx->height, outFrame->data, 
  
              outFrame->linesize);
  
              av_init_packet(&outPacket);
  
              outPacket.data = NULL;    // packet data will be allocated by 
  
              the encoder
  
              outPacket.size = 0;
  
  
  
              outFrame->pts=z;
  
              //encode frame
  
              avcodec_encode_video2(outAVCodecContext , &outPacket ,outFrame , 
  
              &got_picture);
  
  
  
  
  
              if(got_picture)
  
              {
  
                  if(outPacket.pts != AV_NOPTS_VALUE)
  
                      outPacket.pts = av_rescale_q(outPacket.pts, video_st-
  
                      >codec->time_base, video_st->time_base);
  
                  if(outPacket.dts != AV_NOPTS_VALUE)
  
                      outPacket.dts = av_rescale_q(outPacket.dts, video_st-
  
                      >codec->time_base, video_st->time_base);
  
  
  
                  //Write encoded packet to file.
  
                  if(av_write_frame(outAVFormatContext , &outPacket) != 0)
  
                  {
  
                      av_free_packet(pAVPacket);
  
                      av_free_packet(&outPacket);
  
                      return -1;
  
                  }
  
                  z++;
  
                  av_free_packet(&outPacket);
  
              } // got_picture
  
          } // got_picture
  
      }
  
      // If packet is from audio stream
  
      else if (pAVPacket->stream_index == audio_stream_idx)
  
      {
  
         //Write to file without decoding and encoding it
  
         if(av_write_frame(outAVFormatContext , pAVPacket) != 0)
  
          {
  
          }
  
      }
  
      av_free_packet(pAVPacket);
  
      //z++;
  
  }// End of while-loop
  
  
  
  value = av_write_trailer(outAVFormatContext);
  
  if( value < 0)
  
  {
  
      return -1;
  
  }

  I am using below settings :

          outAVCodecContext->codec_id = AV_CODEC_ID_H264;// AV_CODEC_ID_MPEG4; // AV_CODEC_ID_H264 // AV_CODEC_ID_MPEG1VIDEO
  
      outAVCodecContext->bit_rate_tolerance = BIT_RATE_TOLERANT;
  
      outAVCodecContext->rc_max_rate = RC_MAX_RATE;
  
      outAVCodecContext->rc_buffer_size = RC_BUFFER_SIZE;
  
      outAVCodecContext->gop_size = GOP_SIZE;
  
      outAVCodecContext->b_frame_strategy = B_FRAME_STRATEGY;
  
      outAVCodecContext->coder_type = CODER_TYPE;
  
      outAVCodecContext->me_cmp = ME_CMP;
  
      outAVCodecContext->me_range = ME_RANGE; //16
  
      outAVCodecContext->qmin = QMIN;  //10
  
      outAVCodecContext->qmax = QMAX;  //51
  
      outAVCodecContext->scenechange_threshold = SCENECHANGE_THRESHOLD; //40
  
      outAVCodecContext->flags |= CODEC_FLAG_LOOP_FILTER;
  
      outAVCodecContext->me_method = ME_METHOD;
  
      outAVCodecContext->me_subpel_quality = ME_SUBPEL_QUALITY;
  
      outAVCodecContext->i_quant_factor = I_QUANT_FACTOR; //0.71
  
      outAVCodecContext->qcompress = QCOMPRESS;
  
      outAVCodecContext->max_qdiff = MAX_QDIFF;
  
      av_dict_set( &codec_options, "preset", "superfast", 0 );

  And values are defined as below :

  #define VAVLON_VALUES_H
  
  #define BIT_RATE_TOLERANT 0;
  
  #define RC_MAX_RATE 0;
  
  #define RC_BUFFER_SIZE 0;
  
  #define GOP_SIZE 40;
  
  #define B_FRAME_STRATEGY 0;
  
  #define CODER_TYPE 1;
  
  #define ME_CMP 1;
  
  #define ME_RANGE 16; //16
  
  #define QMIN 30;  //37
  
  #define QMAX 40;  //70
  
  #define SCENECHANGE_THRESHOLD 40; //40
  
  #define ME_METHOD ME_HEX;
  
  #define ME_SUBPEL_QUALITY 40;
  
  #define I_QUANT_FACTOR 0.71;
  
  #define QCOMPRESS 0.3;
  
  #define MAX_QDIFF 4;
  
  #define BIT_RATE 500000;
  
  #define CODEC_TYPE AVMEDIA_TYPE_VIDEO;
  
  #define PIX_FMT AV_PIX_FMT_YUV420P;
  
  #define MAX_B_FRAMES 0;
  
  #define NUM 1;
  
  #define DEN 30;

  Above code works as expected when i am encoding .mp4 file but i notice lag in video when i try to encode .3gp file.
  Can you please help in finding out what i am doing wrong ?

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