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• how to stream h.264 video with mp3 audio using libavcodec ?

  18 septembre 2012, par dasg

  I read h.264 frames from webcamera and capture audio from microphone. I need to stream live video to ffserver. During debug I read video from ffserver using ffmpeg with following command :

  ffmpeg -i http://127.0.0.1:12345/robot.avi -vcodec copy -acodec copy out.avi

  My video in output file is slightly accelerated. If I add a audio stream it is accelerated several times. Sometimes there is no audio in the output file.

  Here is my code for encoding audio :

  #include "v_audio_encoder.h"
  
  
  
  extern "C" {
  
  #include <libavcodec></libavcodec>avcodec.h>
  
  }
  
  #include <cassert>
  
  
  
  struct VAudioEncoder::Private
  
  {
  
      AVCodec *m_codec;
  
      AVCodecContext *m_context;
  
  
  
      std::vector m_outBuffer;
  
  };
  
  
  
  VAudioEncoder::VAudioEncoder( int sampleRate, int bitRate )
  
  {
  
      d = new Private( );
  
      d->m_codec = avcodec_find_encoder( CODEC_ID_MP3 );
  
      assert( d->m_codec );
  
      d->m_context = avcodec_alloc_context3( d->m_codec );
  
  
  
      // put sample parameters
  
      d->m_context->channels = 2;
  
      d->m_context->bit_rate = bitRate;
  
      d->m_context->sample_rate = sampleRate;
  
      d->m_context->sample_fmt = AV_SAMPLE_FMT_S16;
  
      strcpy( d->m_context->codec_name, "libmp3lame" );
  
  
  
      // open it
  
      int res = avcodec_open2( d->m_context, d->m_codec, 0 );
  
      assert( res >= 0 );
  
  
  
      d->m_outBuffer.resize( d->m_context->frame_size );
  
  }
  
  
  
  VAudioEncoder::~VAudioEncoder( )
  
  {
  
      avcodec_close( d->m_context );
  
      av_free( d->m_context );
  
      delete d;
  
  }
  
  
  
  void VAudioEncoder::encode( const std::vector&amp; samples, std::vector&amp; outbuf )
  
  {
  
      assert( (int)samples.size( ) == d->m_context->frame_size );
  
  
  
      int outSize = avcodec_encode_audio( d->m_context, d->m_outBuffer.data( ),
  
                                          d->m_outBuffer.size( ), reinterpret_cast<const>( samples.data( ) ) );
  
      if( outSize ) {
  
          outbuf.resize( outSize );
  
          memcpy( outbuf.data( ), d->m_outBuffer.data( ), outSize );
  
      }
  
      else
  
          outbuf.clear( );
  
  }
  
  
  
  int VAudioEncoder::getFrameSize( ) const
  
  {
  
      return d->m_context->frame_size;
  
  }
  
  </const></cassert>

  Here is my code for streaming video :

  #include "v_out_video_stream.h"
  
  
  
  extern "C" {
  
  #include <libavformat></libavformat>avformat.h>
  
  #include <libavutil></libavutil>opt.h>
  
  #include <libavutil></libavutil>avstring.h>
  
  #include <libavformat></libavformat>avio.h>
  
  }
  
  
  
  #include <stdexcept>
  
  #include <cassert>
  
  
  
  struct VStatticRegistrar
  
  {
  
      VStatticRegistrar( )
  
      {
  
          av_register_all( );
  
          avformat_network_init( );
  
      }
  
  };
  
  
  
  VStatticRegistrar __registrar;
  
  
  
  struct VOutVideoStream::Private
  
  {
  
      AVFormatContext * m_context;
  
      int m_videoStreamIndex;
  
      int m_audioStreamIndex;
  
  
  
      int m_videoBitrate;
  
      int m_width;
  
      int m_height;
  
      int m_fps;
  
      int m_bitrate;
  
  
  
      bool m_waitKeyFrame;
  
  };
  
  
  
  VOutVideoStream::VOutVideoStream( int width, int height, int fps, int bitrate )
  
  {
  
      d = new Private( );
  
      d->m_width = width;
  
      d->m_height = height;
  
      d->m_fps = fps;
  
      d->m_context = 0;
  
      d->m_videoStreamIndex = -1;
  
      d->m_audioStreamIndex = -1;
  
      d->m_bitrate = bitrate;
  
      d->m_waitKeyFrame = true;
  
  }
  
  
  
  bool VOutVideoStream::connectToServer( const std::string&amp; uri )
  
  {
  
      assert( ! d->m_context );
  
  
  
      // initalize the AV context
  
      d->m_context = avformat_alloc_context();
  
      if( !d->m_context )
  
          return false;
  
      // get the output format
  
      d->m_context->oformat = av_guess_format( "ffm", NULL, NULL );
  
      if( ! d->m_context->oformat )
  
          return false;
  
  
  
      strcpy( d->m_context->filename, uri.c_str( ) );
  
  
  
      // add an H.264 stream
  
      AVStream *stream = avformat_new_stream( d->m_context, NULL );
  
      if ( ! stream )
  
          return false;
  
      // initalize codec
  
      AVCodecContext* codec = stream->codec;
  
      if( d->m_context->oformat->flags &amp; AVFMT_GLOBALHEADER )
  
          codec->flags |= CODEC_FLAG_GLOBAL_HEADER;
  
      codec->codec_id = CODEC_ID_H264;
  
      codec->codec_type = AVMEDIA_TYPE_VIDEO;
  
      strcpy( codec->codec_name, "libx264" );
  
  //    codec->codec_tag = ( unsigned(&#39;4&#39;) &lt;&lt; 24 ) + (unsigned(&#39;6&#39;) &lt;&lt; 16 ) + ( unsigned(&#39;2&#39;) &lt;&lt; 8 ) + &#39;H&#39;;
  
      codec->width = d->m_width;
  
      codec->height = d->m_height;
  
      codec->time_base.den = d->m_fps;
  
      codec->time_base.num = 1;
  
      codec->bit_rate = d->m_bitrate;
  
      d->m_videoStreamIndex = stream->index;
  
  
  
      // add an MP3 stream
  
      stream = avformat_new_stream( d->m_context, NULL );
  
      if ( ! stream )
  
          return false;
  
      // initalize codec
  
      codec = stream->codec;
  
      if( d->m_context->oformat->flags &amp; AVFMT_GLOBALHEADER )
  
          codec->flags |= CODEC_FLAG_GLOBAL_HEADER;
  
      codec->codec_id = CODEC_ID_MP3;
  
      codec->codec_type = AVMEDIA_TYPE_AUDIO;
  
      strcpy( codec->codec_name, "libmp3lame" );
  
      codec->sample_fmt = AV_SAMPLE_FMT_S16;
  
      codec->channels = 2;
  
      codec->bit_rate = 64000;
  
      codec->sample_rate = 44100;
  
      d->m_audioStreamIndex = stream->index;
  
  
  
      // try to open the stream
  
      if( avio_open( &amp;d->m_context->pb, d->m_context->filename, AVIO_FLAG_WRITE ) &lt; 0 )
  
           return false;
  
  
  
      // write the header
  
      return avformat_write_header( d->m_context, NULL ) == 0;
  
  }
  
  
  
  void VOutVideoStream::disconnect( )
  
  {
  
      assert( d->m_context );
  
  
  
      avio_close( d->m_context->pb );
  
      avformat_free_context( d->m_context );
  
      d->m_context = 0;
  
  }
  
  
  
  VOutVideoStream::~VOutVideoStream( )
  
  {
  
      if( d->m_context )
  
          disconnect( );
  
      delete d;
  
  }
  
  
  
  int VOutVideoStream::getVopType( const std::vector&amp; image )
  
  {
  
      if( image.size( ) &lt; 6 )
  
          return -1;
  
      unsigned char *b = (unsigned char*)image.data( );
  
  
  
      // Verify NAL marker
  
      if( b[ 0 ] || b[ 1 ] || 0x01 != b[ 2 ] ) {
  
          ++b;
  
          if ( b[ 0 ] || b[ 1 ] || 0x01 != b[ 2 ] )
  
              return -1;
  
      }
  
  
  
      b += 3;
  
  
  
      // Verify VOP id
  
      if( 0xb6 == *b ) {
  
          ++b;
  
          return ( *b &amp; 0xc0 ) >> 6;
  
      }
  
  
  
      switch( *b ) {
  
      case 0x65: return 0;
  
      case 0x61: return 1;
  
      case 0x01: return 2;
  
      }
  
  
  
      return -1;
  
  }
  
  
  
  bool VOutVideoStream::sendVideoFrame( std::vector&amp; image )
  
  {
  
      // Init packet
  
      AVPacket pkt;
  
      av_init_packet( &amp;pkt );
  
      pkt.flags |= ( 0 >= getVopType( image ) ) ? AV_PKT_FLAG_KEY : 0;
  
  
  
      // Wait for key frame
  
      if ( d->m_waitKeyFrame ) {
  
          if( pkt.flags &amp; AV_PKT_FLAG_KEY )
  
              d->m_waitKeyFrame = false;
  
          else
  
              return true;
  
      }
  
  
  
      pkt.stream_index = d->m_videoStreamIndex;
  
      pkt.data = image.data( );
  
      pkt.size = image.size( );
  
      pkt.pts = pkt.dts = AV_NOPTS_VALUE;
  
  
  
      return av_write_frame( d->m_context, &amp;pkt ) >= 0;
  
  }
  
  
  
  bool VOutVideoStream::sendAudioFrame( std::vector&amp; audio )
  
  {
  
      // Init packet
  
      AVPacket pkt;
  
      av_init_packet( &amp;pkt );
  
      pkt.stream_index = d->m_audioStreamIndex;
  
      pkt.data = audio.data( );
  
      pkt.size = audio.size( );
  
      pkt.pts = pkt.dts = AV_NOPTS_VALUE;
  
  
  
      return av_write_frame( d->m_context, &amp;pkt ) >= 0;
  
  }
  
  </cassert></stdexcept>

  Here is how I use it :

  BOOST_AUTO_TEST_CASE(testSendingVideo)
  
  {
  
      const int framesToGrab = 90000;
  
  
  
      VOutVideoStream stream( VIDEO_WIDTH, VIDEO_HEIGHT, FPS, VIDEO_BITRATE );
  
      if( stream.connectToServer( URI ) ) {
  
          VAudioEncoder audioEncoder( AUDIO_SAMPLE_RATE, AUDIO_BIT_RATE );
  
          VAudioCapture microphone( MICROPHONE_NAME, AUDIO_SAMPLE_RATE, audioEncoder.getFrameSize( ) );
  
  
  
          VLogitecCamera camera( VIDEO_WIDTH, VIDEO_HEIGHT );
  
          BOOST_REQUIRE( camera.open( CAMERA_PORT ) );
  
          BOOST_REQUIRE( camera.startCapturing( ) );
  
  
  
          std::vector image, encodedAudio;
  
          std::vector voice;
  
          boost::system_time startTime;
  
          int delta;
  
          for( int i = 0; i < framesToGrab; ++i ) {
  
              startTime = boost::posix_time::microsec_clock::universal_time( );
  
  
  
              BOOST_REQUIRE( camera.read( image ) );
  
              BOOST_REQUIRE( microphone.read( voice ) );
  
              audioEncoder.encode( voice, encodedAudio );
  
  
  
              BOOST_REQUIRE( stream.sendVideoFrame( image ) );
  
              BOOST_REQUIRE( stream.sendAudioFrame( encodedAudio ) );
  
  
  
              delta = ( boost::posix_time::microsec_clock::universal_time( ) - startTime ).total_milliseconds( );
  
              if( delta < 1000 / FPS )
  
                  boost::thread::sleep( startTime + boost::posix_time::milliseconds( 1000 / FPS - delta ) );
  
          }
  
  
  
          BOOST_REQUIRE( camera.stopCapturing( ) );
  
          BOOST_REQUIRE( camera.close( ) );
  
      }
  
      else
  
          std::cout << "failed to connect to server" << std::endl;
  
  }

  I think my problem is in PTS and DTS. Can anyone help me ?

• How to write NALs produced by x264_encoder_encode() using ffmpeg av_interleaved_write_frame()

  21 janvier 2013, par Haleeq Usman

  I have been trying to produce a "flv" video file in the following sequence :

  av_register_all();
  
  
  
  // Open video file
  
  if (avformat_open_input(&pFormatCtx, "6.mp4", NULL, NULL) != 0)
  
      return -1; // Couldn't open file
  
  
  
  // Retrieve stream information
  
  if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
  
      return -1; // Couldn't find stream information
  
  
  
  // Dump information about file onto standard error
  
  av_dump_format(pFormatCtx, 0, "input_file.mp4", 0);
  
  
  
  // Find the first video stream
  
  videoStream = -1;
  
  for (i = 0; i < pFormatCtx->nb_streams; i++)
  
      if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
  
          videoStream = i;
  
          break;
  
      }
  
  if (videoStream == -1)
  
      return -1; // Didn't find a video stream
  
  
  
  // Get a pointer to the codec context for the video stream
  
  pCodecCtx = pFormatCtx->streams[videoStream]->codec;
  
  
  
  // Find the decoder for the video stream
  
  pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
  
  if (pCodec == NULL) {
  
      fprintf(stderr, "Unsupported codec!\n");
  
      return -1; // Codec not found
  
  }
  
  // Open codec
  
  if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
  
      return -1; // Could not open codec
  
  
  
  // Allocate video frame
  
  pFrame = avcodec_alloc_frame();
  
  
  
  // Allocate video frame
  
  pFrame = avcodec_alloc_frame();
  
  
  
  // Allocate an AVFrame structure
  
  pFrameYUV420 = avcodec_alloc_frame();
  
  if (pFrameYUV420 == NULL)
  
      return -1;
  
  
  
  // Determine required buffer size and allocate buffer
  
  numBytes = avpicture_get_size(pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height);
  
  buffer = (uint8_t *) av_malloc(numBytes * sizeof(uint8_t));
  
  
  
  // Assign appropriate parts of buffer to image planes in pFrameYUV420
  
  // Note that pFrameYUV420 is an AVFrame, but AVFrame is a superset of AVPicture
  
  avpicture_fill((AVPicture *) pFrameRGB, buffer, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height);
  
  
  
  // Setup scaler
  
  img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, SWS_BILINEAR, 0, 0, 0);
  
  if (img_convert_ctx == NULL) {
  
      fprintf(stderr, "Cannot initialize the conversion context!\n");
  
      exit(1);
  
  }
  
  
  
  // Setup encoder/muxing now
  
  filename = "output_file.flv";
  
  fmt = av_guess_format("flv", filename, NULL);
  
  if (fmt == NULL) {
  
      printf("Could not guess format.\n");
  
      return -1;
  
  }
  
  /* allocate the output media context */
  
  oc = avformat_alloc_context();
  
  if (oc == NULL) {
  
      printf("could not allocate context.\n");
  
      return -1;
  
  }
  
  oc->oformat = fmt;
  
  snprintf(oc->filename, sizeof(oc->filename), "%s", filename);
  
  
  
  video_st = NULL;
  
  if (fmt->video_codec != AV_CODEC_ID_NONE) {
  
      video_st = add_stream(oc, &video_codec, fmt->video_codec);
  
  }
  
  
  
  // Let's see some information about our format
  
  av_dump_format(oc, 0, filename, 1);
  
  
  
  /* open the output file, if needed */
  
  if (!(fmt->flags & AVFMT_NOFILE)) {
  
      ret = avio_open(&oc->pb, filename, AVIO_FLAG_WRITE);
  
      if (ret < 0) {
  
          fprintf(stderr, "Could not open '%s': %s\n", filename, av_err2str(ret));
  
          return 1;
  
      }
  
      }
  
  /* Write the stream header, if any. */
  
  ret = avformat_write_header(oc, NULL);
  
  if (ret < 0) {
  
      fprintf(stderr, "Error occurred when opening output file: %s\n", av_err2str(ret));
  
      return 1;
  
  }
  
  
  
  // Setup x264 params
  
  x264_param_t param;
  
  x264_param_default_preset(&param, "veryfast", "zerolatency");
  
  param.i_threads = 1;
  
  param.i_width = video_st->codec->width;
  
  param.i_height = video_st->codec->height;
  
  param.i_fps_num = STREAM_FRAME_RATE; // 30 fps, same as video
  
  param.i_fps_den = 1;
  
  // Intra refres:
  
  param.i_keyint_max = STREAM_FRAME_RATE;
  
  param.b_intra_refresh = 1;
  
  // Rate control:
  
  param.rc.i_rc_method = X264_RC_CRF;
  
  param.rc.f_rf_constant = 25;
  
  param.rc.f_rf_constant_max = 35;
  
  // For streaming:
  
  param.b_repeat_headers = 1;
  
  param.b_annexb = 1;
  
  x264_param_apply_profile(&param, "baseline");
  
  
  
  x264_t* encoder = x264_encoder_open(&param);
  
  x264_picture_t pic_in, pic_out;
  
  x264_picture_alloc(&pic_in, X264_CSP_I420, video_st->codec->width, video_st->codec->height);
  
  
  
  x264_nal_t* nals;
  
  int i_nals;
  
  
  
  // The loop:
  
  // 1. Read frames
  
  // 2. Decode the frame
  
  // 3. Attempt to re-encode using x264
  
  // 4. Write the x264 encoded frame using av_interleaved_write_frame
  
  while (av_read_frame(pFormatCtx, &packet) >= 0) {
  
      // Is this a packet from the video stream?
  
      if (packet.stream_index == videoStream) {
  
          // Decode video frame
  
          avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
  
  
  
          // Did we get a video frame?
  
          if (frameFinished) {
  
              sws_scale(img_convert_ctx, pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pic_in.img.plane, pic_in.img.i_stride);
  
              int frame_size = x264_encoder_encode(encoder, &nals, &i_nals, &pic_in, &pic_out);
  
  
  
              if (frame_size >= 0) {
  
                  if (i_nals < 0)
  
                      printf("invalid frame size: %d\n", i_nals);
  
                  // write out NALs
  
                  for (i = 0; i < i_nals; i++) {
  
                      // initalize a packet
  
                      AVPacket p;
  
                      av_init_packet(&p);
  
                      p.data = nals[i].p_payload;
  
                      p.size = nals[i].i_payload;
  
                      p.stream_index = video_st->index;
  
                      p.flags = AV_PKT_FLAG_KEY;
  
                      p.pts = AV_NOPTS_VALUE;
  
                      p.dts = AV_NOPTS_VALUE;
  
                      ret = av_interleaved_write_frame(oc, &p);
  
                  }
  
              }
  
              printf("encoded frame #%d\n", frame_count);
  
              frame_count++;
  
          }
  
      }
  
  
  
      // Free the packet that was allocated by av_read_frame
  
      av_free_packet(&packet);
  
  }
  
  
  
  // Now we free up resources used/close codecs, and finally close our program.

  Here is the implementation for the add_stream() function :

  /* Add an output stream. */
  
  static AVStream *add_stream(AVFormatContext *oc, AVCodec **codec, enum AVCodecID codec_id) {
  
      AVCodecContext *c;
  
      AVStream *st;
  
      int r;
  
      /* find the encoder */
  
      *codec = avcodec_find_encoder(codec_id);
  
      if (!(*codec)) {
  
          fprintf(stderr, "Could not find encoder for '%s'\n",
  
                  avcodec_get_name(codec_id));
  
          exit(1);
  
      }
  
      st = avformat_new_stream(oc, *codec);
  
      if (!st) {
  
          fprintf(stderr, "Could not allocate stream\n");
  
          exit(1);
  
      }
  
      st->id = oc->nb_streams - 1;
  
      c = st->codec;
  
      switch ((*codec)->type) {
  
      case AVMEDIA_TYPE_AUDIO:
  
          st->id = 1;
  
          c->sample_fmt = AV_SAMPLE_FMT_FLTP;
  
          c->bit_rate = 64000;
  
          c->sample_rate = 44100;
  
          c->channels = 2;
  
          break;
  
      case AVMEDIA_TYPE_VIDEO:
  
          avcodec_get_context_defaults3(c, *codec);
  
          c->codec_id = codec_id;
  
          c->bit_rate = 500*1000;
  
          //c->rc_min_rate = 500*1000;
  
          //c->rc_max_rate = 500*1000;
  
          //c->rc_buffer_size = 500*1000;
  
          /* Resolution must be a multiple of two. */
  
          c->width = 1280;
  
          c->height = 720;
  
          /* timebase: This is the fundamental unit of time (in seconds) in terms
  
           * of which frame timestamps are represented. For fixed-fps content,
  
           * timebase should be 1/framerate and timestamp increments should be
  
           * identical to 1. */
  
          c->time_base.den = STREAM_FRAME_RATE;
  
          c->time_base.num = 1;
  
          c->gop_size = 12; /* emit one intra frame every twelve frames at most */
  
          c->pix_fmt = STREAM_PIX_FMT;
  
          if (c->codec_id == AV_CODEC_ID_MPEG2VIDEO) {
  
              /* just for testing, we also add B frames */
  
              c->max_b_frames = 2;
  
          }
  
          if (c->codec_id == AV_CODEC_ID_MPEG1VIDEO) {
  
              /* Needed to avoid using macroblocks in which some coeffs overflow.
  
               * This does not happen with normal video, it just happens here as
  
               * the motion of the chroma plane does not match the luma plane. */
  
              c->mb_decision = 2;
  
          }
  
          break;
  
      default:
  
          break;
  
      }
  
      /* Some formats want stream headers to be separate. */
  
      if (oc->oformat->flags & AVFMT_GLOBALHEADER)
  
          c->flags |= CODEC_FLAG_GLOBAL_HEADER;
  
      return st;
  
  }

  After the encoding is complete, I check the output file output_file.flv. I notice it's size is very large : 101MB and it does not play. If I use ffmpeg to decode/encode the input file, then I get an output file about 83MB in size (which is about the same size as the original .mp4 file used as input). Also, the 83MB output from just using ffmpeg C api, as opposed to using x264 for the encoding step, plays just fine. Does anyone know where I am going wrong ? I have tried researching this for a few days now but with no luck :(. I feel that I am close to making it work, however, I just cannot figure out what I am doing wrong. Thank you !

• How to write NALs produced by x264_encoder_encode() using ffmpeg av_interleaved_write_frame()

  21 janvier 2013, par Haleeq Usman

  I have been trying to produce a "flv" video file in the following sequence :

  av_register_all();
  
  
  
  // Open video file
  
  if (avformat_open_input(&pFormatCtx, "6.mp4", NULL, NULL) != 0)
  
      return -1; // Couldn't open file
  
  
  
  // Retrieve stream information
  
  if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
  
      return -1; // Couldn't find stream information
  
  
  
  // Dump information about file onto standard error
  
  av_dump_format(pFormatCtx, 0, "input_file.mp4", 0);
  
  
  
  // Find the first video stream
  
  videoStream = -1;
  
  for (i = 0; i < pFormatCtx->nb_streams; i++)
  
      if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
  
          videoStream = i;
  
          break;
  
      }
  
  if (videoStream == -1)
  
      return -1; // Didn't find a video stream
  
  
  
  // Get a pointer to the codec context for the video stream
  
  pCodecCtx = pFormatCtx->streams[videoStream]->codec;
  
  
  
  // Find the decoder for the video stream
  
  pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
  
  if (pCodec == NULL) {
  
      fprintf(stderr, "Unsupported codec!\n");
  
      return -1; // Codec not found
  
  }
  
  // Open codec
  
  if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
  
      return -1; // Could not open codec
  
  
  
  // Allocate video frame
  
  pFrame = avcodec_alloc_frame();
  
  
  
  // Allocate video frame
  
  pFrame = avcodec_alloc_frame();
  
  
  
  // Allocate an AVFrame structure
  
  pFrameYUV420 = avcodec_alloc_frame();
  
  if (pFrameYUV420 == NULL)
  
      return -1;
  
  
  
  // Determine required buffer size and allocate buffer
  
  numBytes = avpicture_get_size(pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height);
  
  buffer = (uint8_t *) av_malloc(numBytes * sizeof(uint8_t));
  
  
  
  // Assign appropriate parts of buffer to image planes in pFrameYUV420
  
  // Note that pFrameYUV420 is an AVFrame, but AVFrame is a superset of AVPicture
  
  avpicture_fill((AVPicture *) pFrameRGB, buffer, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height);
  
  
  
  // Setup scaler
  
  img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, SWS_BILINEAR, 0, 0, 0);
  
  if (img_convert_ctx == NULL) {
  
      fprintf(stderr, "Cannot initialize the conversion context!\n");
  
      exit(1);
  
  }
  
  
  
  // Setup encoder/muxing now
  
  filename = "output_file.flv";
  
  fmt = av_guess_format("flv", filename, NULL);
  
  if (fmt == NULL) {
  
      printf("Could not guess format.\n");
  
      return -1;
  
  }
  
  /* allocate the output media context */
  
  oc = avformat_alloc_context();
  
  if (oc == NULL) {
  
      printf("could not allocate context.\n");
  
      return -1;
  
  }
  
  oc->oformat = fmt;
  
  snprintf(oc->filename, sizeof(oc->filename), "%s", filename);
  
  
  
  video_st = NULL;
  
  if (fmt->video_codec != AV_CODEC_ID_NONE) {
  
      video_st = add_stream(oc, &video_codec, fmt->video_codec);
  
  }
  
  
  
  // Let's see some information about our format
  
  av_dump_format(oc, 0, filename, 1);
  
  
  
  /* open the output file, if needed */
  
  if (!(fmt->flags & AVFMT_NOFILE)) {
  
      ret = avio_open(&oc->pb, filename, AVIO_FLAG_WRITE);
  
      if (ret < 0) {
  
          fprintf(stderr, "Could not open '%s': %s\n", filename, av_err2str(ret));
  
          return 1;
  
      }
  
      }
  
  /* Write the stream header, if any. */
  
  ret = avformat_write_header(oc, NULL);
  
  if (ret < 0) {
  
      fprintf(stderr, "Error occurred when opening output file: %s\n", av_err2str(ret));
  
      return 1;
  
  }
  
  
  
  // Setup x264 params
  
  x264_param_t param;
  
  x264_param_default_preset(&param, "veryfast", "zerolatency");
  
  param.i_threads = 1;
  
  param.i_width = video_st->codec->width;
  
  param.i_height = video_st->codec->height;
  
  param.i_fps_num = STREAM_FRAME_RATE; // 30 fps, same as video
  
  param.i_fps_den = 1;
  
  // Intra refres:
  
  param.i_keyint_max = STREAM_FRAME_RATE;
  
  param.b_intra_refresh = 1;
  
  // Rate control:
  
  param.rc.i_rc_method = X264_RC_CRF;
  
  param.rc.f_rf_constant = 25;
  
  param.rc.f_rf_constant_max = 35;
  
  // For streaming:
  
  param.b_repeat_headers = 1;
  
  param.b_annexb = 1;
  
  x264_param_apply_profile(&param, "baseline");
  
  
  
  x264_t* encoder = x264_encoder_open(&param);
  
  x264_picture_t pic_in, pic_out;
  
  x264_picture_alloc(&pic_in, X264_CSP_I420, video_st->codec->width, video_st->codec->height);
  
  
  
  x264_nal_t* nals;
  
  int i_nals;
  
  
  
  // The loop:
  
  // 1. Read frames
  
  // 2. Decode the frame
  
  // 3. Attempt to re-encode using x264
  
  // 4. Write the x264 encoded frame using av_interleaved_write_frame
  
  while (av_read_frame(pFormatCtx, &packet) >= 0) {
  
      // Is this a packet from the video stream?
  
      if (packet.stream_index == videoStream) {
  
          // Decode video frame
  
          avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
  
  
  
          // Did we get a video frame?
  
          if (frameFinished) {
  
              sws_scale(img_convert_ctx, pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pic_in.img.plane, pic_in.img.i_stride);
  
              int frame_size = x264_encoder_encode(encoder, &nals, &i_nals, &pic_in, &pic_out);
  
  
  
              if (frame_size >= 0) {
  
                  if (i_nals < 0)
  
                      printf("invalid frame size: %d\n", i_nals);
  
                  // write out NALs
  
                  for (i = 0; i < i_nals; i++) {
  
                      // initalize a packet
  
                      AVPacket p;
  
                      av_init_packet(&p);
  
                      p.data = nals[i].p_payload;
  
                      p.size = nals[i].i_payload;
  
                      p.stream_index = video_st->index;
  
                      p.flags = AV_PKT_FLAG_KEY;
  
                      p.pts = AV_NOPTS_VALUE;
  
                      p.dts = AV_NOPTS_VALUE;
  
                      ret = av_interleaved_write_frame(oc, &p);
  
                  }
  
              }
  
              printf("encoded frame #%d\n", frame_count);
  
              frame_count++;
  
          }
  
      }
  
  
  
      // Free the packet that was allocated by av_read_frame
  
      av_free_packet(&packet);
  
  }
  
  
  
  // Now we free up resources used/close codecs, and finally close our program.

  Here is the implementation for the add_stream() function :

  /* Add an output stream. */
  
  static AVStream *add_stream(AVFormatContext *oc, AVCodec **codec, enum AVCodecID codec_id) {
  
      AVCodecContext *c;
  
      AVStream *st;
  
      int r;
  
      /* find the encoder */
  
      *codec = avcodec_find_encoder(codec_id);
  
      if (!(*codec)) {
  
          fprintf(stderr, "Could not find encoder for '%s'\n",
  
                  avcodec_get_name(codec_id));
  
          exit(1);
  
      }
  
      st = avformat_new_stream(oc, *codec);
  
      if (!st) {
  
          fprintf(stderr, "Could not allocate stream\n");
  
          exit(1);
  
      }
  
      st->id = oc->nb_streams - 1;
  
      c = st->codec;
  
      switch ((*codec)->type) {
  
      case AVMEDIA_TYPE_AUDIO:
  
          st->id = 1;
  
          c->sample_fmt = AV_SAMPLE_FMT_FLTP;
  
          c->bit_rate = 64000;
  
          c->sample_rate = 44100;
  
          c->channels = 2;
  
          break;
  
      case AVMEDIA_TYPE_VIDEO:
  
          avcodec_get_context_defaults3(c, *codec);
  
          c->codec_id = codec_id;
  
          c->bit_rate = 500*1000;
  
          //c->rc_min_rate = 500*1000;
  
          //c->rc_max_rate = 500*1000;
  
          //c->rc_buffer_size = 500*1000;
  
          /* Resolution must be a multiple of two. */
  
          c->width = 1280;
  
          c->height = 720;
  
          /* timebase: This is the fundamental unit of time (in seconds) in terms
  
           * of which frame timestamps are represented. For fixed-fps content,
  
           * timebase should be 1/framerate and timestamp increments should be
  
           * identical to 1. */
  
          c->time_base.den = STREAM_FRAME_RATE;
  
          c->time_base.num = 1;
  
          c->gop_size = 12; /* emit one intra frame every twelve frames at most */
  
          c->pix_fmt = STREAM_PIX_FMT;
  
          if (c->codec_id == AV_CODEC_ID_MPEG2VIDEO) {
  
              /* just for testing, we also add B frames */
  
              c->max_b_frames = 2;
  
          }
  
          if (c->codec_id == AV_CODEC_ID_MPEG1VIDEO) {
  
              /* Needed to avoid using macroblocks in which some coeffs overflow.
  
               * This does not happen with normal video, it just happens here as
  
               * the motion of the chroma plane does not match the luma plane. */
  
              c->mb_decision = 2;
  
          }
  
          break;
  
      default:
  
          break;
  
      }
  
      /* Some formats want stream headers to be separate. */
  
      if (oc->oformat->flags & AVFMT_GLOBALHEADER)
  
          c->flags |= CODEC_FLAG_GLOBAL_HEADER;
  
      return st;
  
  }

  After the encoding is complete, I check the output file output_file.flv. I notice it's size is very large : 101MB and it does not play. If I use ffmpeg to decode/encode the input file, then I get an output file about 83MB in size (which is about the same size as the original .mp4 file used as input). Also, the 83MB output from just using ffmpeg C api, as opposed to using x264 for the encoding step, plays just fine. Does anyone know where I am going wrong ? I have tried researching this for a few days now but with no luck :(. I feel that I am close to making it work, however, I just cannot figure out what I am doing wrong. Thank you !