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• How to decode mp4 file and encode it to mp4 container using h264 codec in cpp ?

  17 juillet 2017, par Herdesh Verma

  I am developing a cpp program which will take mp4 video file as input, decode it and encode it again using H264 codec.
  Below is the program i have developed so far.

  extern "C"
  
  {
  
  #include <libavutil></libavutil>imgutils.h>
  
  #include <libavutil></libavutil>opt.h>
  
  #include <libavcodec></libavcodec>avcodec.h>
  
  #include <libavutil></libavutil>mathematics.h>
  
  #include <libavutil></libavutil>samplefmt.h>
  
  #include <libavutil></libavutil>timestamp.h>
  
  #include <libavformat></libavformat>avformat.h>
  
  #include <libavfilter></libavfilter>avfiltergraph.h>
  
  #include <libswscale></libswscale>swscale.h>
  
  }
  
  #include 
  
  static AVFormatContext *fmt_ctx = NULL;
  
  
  
  static int frame_index = 0;
  
  
  
  static AVDictionary *pMetaData = NULL;
  
  
  
  static int j = 0, nbytes=0;
  
  uint8_t *video_outbuf = NULL;
  
  static AVPacket *pAVPacket=NULL;
  
  static int value=0;
  
  static AVFrame *pAVFrame=NULL;
  
  static AVFrame *outFrame=NULL;
  
  static AVStream *video_st=NULL;
  
  static AVFormatContext *outAVFormatContext=NULL;
  
  static AVCodec *outAVCodec=NULL;
  
  static AVOutputFormat *output_format=NULL;
  
  static AVCodecContext *video_dec_ctx = NULL, *audio_dec_ctx;
  
  static AVCodecContext *outAVCodecContext=NULL;
  
  static int width, height;
  
  static enum AVPixelFormat pix_fmt;
  
  static AVStream *video_stream = NULL, *audio_stream = NULL;
  
  static const char *src_filename = NULL;
  
  static const char *video_dst_filename = NULL;
  
  static const char *audio_dst_filename = NULL;
  
  static FILE *video_dst_file = NULL;
  
  static FILE *audio_dst_file = NULL;
  
  static uint8_t *video_dst_data[4] = {NULL};
  
  static int      video_dst_linesize[4];
  
  static int video_dst_bufsize;
  
  static int video_stream_idx = -1, audio_stream_idx = -1;
  
  static AVPacket *pkt=NULL;
  
  static AVPacket *pkt1=NULL;
  
  static AVFrame *frame = NULL;
  
  //static AVPacket pkt;
  
  static int video_frame_count = 0;
  
  static int audio_frame_count = 0;
  
  static int refcount = 0;
  
  AVCodec *codec;
  
  static struct SwsContext *sws_ctx;
  
   AVCodecContext *c= NULL;
  
   int i, out_size, size, x, y, outbuf_size;
  
   AVFrame *picture;
  
   uint8_t *outbuf, *picture_buf;
  
  int video_outbuf_size;
  
  int w, h;
  
  AVPixelFormat pixFmt;
  
  uint8_t *data[4];
  
  int linesize[4];
  
  
  
  static int open_codec_context(int *stream_idx,
  
                            AVCodecContext **dec_ctx, AVFormatContext 
  
  *fmt_ctx, enum AVMediaType type)
  
  {
  
  int ret, stream_index;
  
  AVStream *st;
  
  AVCodec *dec = NULL;
  
  AVDictionary *opts = NULL;
  
  ret = av_find_best_stream(fmt_ctx, type, -1, -1, NULL, 0);
  
  if (ret &lt; 0) {
  
      printf("Could not find %s stream in input file '%s'\n",
  
              av_get_media_type_string(type), src_filename);
  
      return ret;
  
  } else {
  
      stream_index = ret;
  
      st = fmt_ctx->streams[stream_index];
  
      /* find decoder for the stream */
  
      dec = avcodec_find_decoder(st->codecpar->codec_id);
  
      if (!dec) {
  
          printf("Failed to find %s codec\n",
  
                  av_get_media_type_string(type));
  
          return AVERROR(EINVAL);
  
      }
  
      /* Allocate a codec context for the decoder */
  
      *dec_ctx = avcodec_alloc_context3(dec);
  
      if (!*dec_ctx) {
  
          printf("Failed to allocate the %s codec context\n",
  
                  av_get_media_type_string(type));
  
          return AVERROR(ENOMEM);
  
      }
  
      /* Copy codec parameters from input stream to output codec context */
  
      if ((ret = avcodec_parameters_to_context(*dec_ctx, st->codecpar)) &lt; 0) {
  
          printf("Failed to copy %s codec parameters to decoder context\n",
  
                  av_get_media_type_string(type));
  
          return ret;
  
      }
  
      /* Init the decoders, with or without reference counting */
  
      av_dict_set(&amp;opts, "refcounted_frames", refcount ? "1" : "0", 0);
  
      if ((ret = avcodec_open2(*dec_ctx, dec, &amp;opts)) &lt; 0) {
  
          printf("Failed to open %s codec\n",
  
                  av_get_media_type_string(type));
  
          return ret;
  
      }
  
      *stream_idx = stream_index;
  
  }
  
  return 0;
  
  }
  
  
  
  
  
  
  
  int main (int argc, char **argv)
  
  {
  
  int ret = 0, got_frame;
  
  src_filename = argv[1];
  
  video_dst_filename = argv[2];
  
  audio_dst_filename = argv[3];
  
  av_register_all();
  
  avcodec_register_all();
  
  printf("Registered all\n");
  
  
  
  /* open input file, and allocate format context */
  
  if (avformat_open_input(&amp;fmt_ctx, src_filename, NULL, NULL) &lt; 0) {
  
      printf("Could not open source file %s\n", src_filename);
  
      exit(1);
  
  }
  
  
  
  /* retrieve stream information */
  
  if (avformat_find_stream_info(fmt_ctx, NULL) &lt; 0) {
  
      printf("Could not find stream information\n");
  
      exit(1);
  
  }
  
  
  
  if (open_codec_context(&amp;video_stream_idx, &amp;video_dec_ctx, fmt_ctx, 
  
  AVMEDIA_TYPE_VIDEO) >= 0) {
  
      video_stream = fmt_ctx->streams[video_stream_idx];
  
      avformat_alloc_output_context2(&amp;outAVFormatContext, NULL, NULL, 
  
  video_dst_filename);
  
      if (!outAVFormatContext)
  
      {
  
              printf("\n\nError : avformat_alloc_output_context2()");
  
              return -1;
  
      }
  
  }
  
  
  
  if (open_codec_context(&amp;audio_stream_idx, &amp;audio_dec_ctx, fmt_ctx, 
  
  AVMEDIA_TYPE_AUDIO) >= 0) {
  
      audio_stream = fmt_ctx->streams[audio_stream_idx];
  
      audio_dst_file = fopen(audio_dst_filename, "wb");
  
      if (!audio_dst_file) {
  
          printf("Could not open destination file %s\n", audio_dst_filename);
  
          ret = 1;
  
          goto end;
  
      }
  
  }
  
  /* dump input information to stderr */
  
      printf("Source file dump starts-----------------------\n");
  
  av_dump_format(fmt_ctx, 0, src_filename, 0);
  
      printf("Source file dump ends-----------------------\n");
  
  
  
  if (!audio_stream &amp;&amp; !video_stream) {
  
      printf("Could not find audio or video stream in the input, aborting\n");
  
      ret = 1;
  
      goto end;
  
  }
  
  
  
      output_format = av_guess_format(NULL, video_dst_filename, NULL);
  
      if( !output_format )
  
      {
  
       printf("\n\nError : av_guess_format()");
  
       return -1;
  
      }
  
  
  
      video_st = avformat_new_stream(outAVFormatContext ,NULL);
  
      if( !video_st )
  
      {
  
              printf("\n\nError : avformat_new_stream()");
  
        return -1;
  
      }
  
  
  
  
  
  
  
      outAVCodec = avcodec_find_encoder(AV_CODEC_ID_H264);
  
      if( !outAVCodec )
  
      {
  
       printf("\n\nError : avcodec_find_encoder()");
  
       return -1;
  
      }
  
      outAVCodecContext = avcodec_alloc_context3(outAVCodec);
  
      if( !outAVCodecContext )
  
      {
  
        printf("\n\nError : avcodec_alloc_context3()");
  
        return -1;
  
      }
  
  
  
      printf("Width=%d Height=%d\n",video_dec_ctx->width, video_dec_ctx-
  
  >height);
  
  
  
      outAVCodecContext = video_st->codec;
  
      outAVCodecContext->codec_id = AV_CODEC_ID_H264;// AV_CODEC_ID_MPEG4; // 
  
  AV_CODEC_ID_H264 // AV_CODEC_ID_MPEG1VIDEO
  
      outAVCodecContext->codec_type = AVMEDIA_TYPE_VIDEO;
  
      outAVCodecContext->pix_fmt  = AV_PIX_FMT_YUV420P;
  
      outAVCodecContext->bit_rate = 350000; // 2500000
  
      outAVCodecContext->width = video_dec_ctx->width;
  
      outAVCodecContext->height = video_dec_ctx->height;
  
      //outAVCodecContext->width = 720;
  
      //outAVCodecContext->height = 480;
  
      outAVCodecContext->gop_size = 100;
  
      outAVCodecContext->max_b_frames = 0;
  
      outAVCodecContext->time_base.num = 1;
  
      outAVCodecContext->time_base.den = 25; // 15fps
  
  
  
      if (outAVCodecContext->codec_id == AV_CODEC_ID_H264)
  
      {
  
              printf("HERE");
  
      //outAVCodecContext->me_range = 16;
  
      //outAVCodecContext->max_qdiff = 4;
  
      outAVCodecContext->qmin = 10;
  
      outAVCodecContext->qmax = 51;
  
      outAVCodecContext->qcompress = 0.1;
  
       av_opt_set(outAVCodecContext->priv_data, "preset", "slow", 0);
  
      av_opt_set(outAVCodecContext->priv_data, "profile", "baseline", 
  
  AV_OPT_SEARCH_CHILDREN);
  
      }
  
      if ( outAVFormatContext->oformat->flags &amp; AVFMT_GLOBALHEADER)
  
      {
  
              outAVCodecContext->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
  
      }
  
  
  
      value = avcodec_open2(outAVCodecContext, outAVCodec, NULL);
  
      if( value &lt; 0)
  
      {
  
              printf("\n\nError : avcodec_open2()=%d", value);
  
              return -1;
  
      }
  
  
  
      outAVFormatContext->metadata = fmt_ctx->metadata;
  
      //outAVFormatContext->streams[video_stream_idx]->metadata=fmt_ctx-
  
  >streams[video_stream_idx]->metadata;
  
      av_dict_set(&amp;(outAVFormatContext->streams[video_stream_idx]->metadata), 
  
  "rotate", "90", 0);
  
  /* create empty video file */
  
      if ( !(outAVFormatContext->flags &amp; AVFMT_NOFILE) )
  
      {
  
       if( avio_open2(&amp;outAVFormatContext->pb , video_dst_filename, 
  
   AVIO_FLAG_WRITE ,NULL, NULL) &lt; 0 )
  
       {
  
        printf("\n\nError : avio_open2()");
  
       }
  
      }
  
  
  
      if(!outAVFormatContext->nb_streams)
  
      {
  
              printf("\n\nError : Output file dose not contain any stream");
  
        return -1;
  
      }
  
  
  
      value = avformat_write_header(outAVFormatContext , NULL);
  
      if(value &lt; 0)
  
      {
  
              printf("\n\nError : avformat_write_header()");
  
              return -1;
  
      }
  
  
  
      printf("\n\nOutput file information :\n\n");
  
      av_dump_format(outAVFormatContext , 0 ,video_dst_filename ,1);
  
  
  
  
  
      int flag;
  
      int frameFinished;
  
      value = 0;
  
  
  
      pAVPacket = (AVPacket *)av_malloc(sizeof(AVPacket));
  
      av_init_packet(pAVPacket);
  
  
  
      pAVFrame = av_frame_alloc();
  
      if( !pAVFrame )
  
      {
  
       printf("\n\nError : av_frame_alloc()");
  
       return -1;
  
      }
  
  
  
  
  
      outFrame = av_frame_alloc();//Allocate an AVFrame and set its fields to 
  
  default values.
  
      if( !outFrame )
  
      {
  
       printf("\n\nError : av_frame_alloc()");
  
       return -1;
  
      }
  
      outFrame->format = outAVCodecContext->pix_fmt;
  
      outFrame->width  = outAVCodecContext->width;
  
      outFrame->height = outAVCodecContext->height;
  
  
  
      nbytes = av_image_get_buffer_size(outAVCodecContext-
  
  >pix_fmt,outAVCodecContext->width,outAVCodecContext->height,32);
  
      video_outbuf = (uint8_t*)av_malloc(nbytes);
  
      if( video_outbuf == NULL )
  
      {
  
      printf("\n\nError : av_malloc()");
  
      }
  
  
  
      // Setup the data pointers and linesizes based on the specified image 
  
  parameters and the provided array.
  
      value = av_image_fill_arrays( outFrame->data, outFrame->linesize, 
  
  video_outbuf , AV_PIX_FMT_YUV420P, outAVCodecContext-
  
  >width,outAVCodecContext->height,1 ); // returns : the size in bytes 
  
  required for src
  
      if(value &lt; 0)
  
      {
  
      printf("\n\nError : av_image_fill_arrays()");
  
      }
  
  
  
      SwsContext* swsCtx_ ;
  
  
  
      // Allocate and return swsContext.
  
      // a pointer to an allocated context, or NULL in case of error
  
      // Deprecated : Use sws_getCachedContext() instead.
  
      swsCtx_ = sws_getContext(video_dec_ctx->width,
  
                              video_dec_ctx->height,
  
                              video_dec_ctx->pix_fmt,
  
                              video_dec_ctx->width,
  
                              video_dec_ctx->height,
  
                              video_dec_ctx->pix_fmt,
  
                              SWS_BICUBIC, NULL, NULL, NULL);
  
  
  
  
  
      AVPacket outPacket;
  
  
  
      int got_picture;
  
  
  
      while( av_read_frame( fmt_ctx , pAVPacket ) >= 0 )
  
      {
  
              printf("Starting of while\n");
  
              if(pAVPacket->stream_index == video_stream_idx)
  
              {
  
                      value = avcodec_decode_video2(video_dec_ctx , pAVFrame , 
  
  &amp;frameFinished , pAVPacket );
  
                      if( value &lt; 0)
  
                      {
  
                              printf("Error : avcodec_decode_video2()");
  
                      }
  
  
  
                      if(frameFinished)// Frame successfully decoded :)
  
                      {
  
                              sws_scale(swsCtx_, pAVFrame->data, pAVFrame-
  
  >linesize,0, video_dec_ctx->height, outFrame->data,outFrame->linesize);
  
  //                              sws_scale(swsCtx_, pAVFrame->data, pAVFrame-
  
  >linesize,0, video_dec_ctx->height, outFrame->data,outFrame->linesize);
  
                              av_init_packet(&amp;outPacket);
  
                              outPacket.data = NULL;    // packet data will be 
  
  allocated by the encoder
  
                              outPacket.size = 0;
  
  
  
                              avcodec_encode_video2(outAVCodecContext , 
  
  &amp;outPacket ,outFrame , &amp;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);
  
  
  
                                      printf("Write frame %3d (size= %2d)\n", 
  
  j++, outPacket.size/1000);
  
                                      if(av_write_frame(outAVFormatContext , 
  
  &amp;outPacket) != 0)
  
                                      {
  
                                              printf("\n\nError : 
  
  av_write_frame()");
  
                                      }
  
  
  
                              av_packet_unref(&amp;outPacket);
  
                              } // got_picture
  
  
  
                      av_packet_unref(&amp;outPacket);
  
                      } // got_picture
  
              }
  
              printf("Ending of while\n");
  
      }// End of while-loop
  
      /* get the delayed frames */
  
  for (got_picture = 1; got_picture; i++) {
  
      //fflush(stdout);
  
      ret = avcodec_encode_video2(outAVCodecContext, &amp;outPacket, NULL, 
  
  &amp;got_picture);
  
      if (ret &lt; 0) {
  
          printf("Error encoding frame\n");
  
          exit(1);
  
      }
  
      if (got_picture) {
  
          printf("Write frame %3d (size=%5d)\n", i, outPacket.size);
  
          av_write_frame(outAVFormatContext , &amp;outPacket);
  
          av_free_packet(&amp;outPacket);
  
      }
  
  }
  
  
  
      value = av_write_trailer(outAVFormatContext);
  
      if( value &lt; 0)
  
      {
  
              printf("\n\nError : av_write_trailer()");
  
      }
  
  
  
      //THIS WAS ADDED LATER
  
      av_free(video_outbuf);
  
  
  
  end:
  
      avcodec_free_context(&amp;video_dec_ctx);
  
      avcodec_free_context(&amp;audio_dec_ctx);
  
      avformat_close_input(&amp;fmt_ctx);
  
      if (video_dst_file)
  
          fclose(video_dst_file);
  
      if (audio_dst_file)
  
          fclose(audio_dst_file);
  
  //  av_frame_free(&amp;frame);
  
      av_free(video_dst_data[0]);
  
      return ret &lt; 0;
  
  }

  Above code is generating a mp4 file but it is not playing.
  Can someone please tell me what i am doing wrong ?

• 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>

• 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>