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• Why is the AV_PARSER_PARSE2 in ffmpeg returning empty AVPacket data for HEVC video ?

  3 août 2019, par HAlmawi

  I’m attempting to decode an HEVC encoded video (.mp4 format) and extract all the frames in C++. I installed ffmpeg and used one of their examples "video_decode.c", however the AVPacket data (pkt->data) is always NULL/empty and the size of the packet (pkt->size) is always 0.

  I have executed ffprobe on the video examples used to ensure that the videos were truly in HEVC format.

  I defined the width, height, pixel format, bit rate, and time base of the AVCodec.

  I initialized the AVPacket data to NULL and size to 0 manually.

  const char *filename, *outfilename;
  
  const AVCodec *codec;
  
  AVCodecParserContext *parser;
  
  AVCodecContext *c = NULL;
  
  FILE *f;
  
  AVFrame *frame;
  
  uint8_t inbuf[INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
  
  uint8_t *data;
  
  size_t   data_size;
  
  int ret;
  
  AVPacket *pkt;
  
  
  
  filename = "C:\\Users\\Me\\Downloads\\video_x265.mp4";
  
  outfilename = "E:\\output\\test%d.pgm";
  
  
  
  pkt = av_packet_alloc();
  
  if (!pkt)
  
      exit(1);
  
  //pkt->data = NULL;
  
  //pkt->size = 0;
  
  /* set end of buffer to 0 (this ensures that no overreading happens for damaged MPEG streams) */
  
  memset(inbuf + INBUF_SIZE, 0, AV_INPUT_BUFFER_PADDING_SIZE);
  
  
  
  /* find the MPEG-1 video decoder */
  
  codec = avcodec_find_decoder(AV_CODEC_ID_HEVC);
  
  if (!codec) {
  
      fprintf(stderr, "Codec not found\n");
  
      exit(1);
  
  }
  
  
  
  parser = av_parser_init(codec->id);
  
  if (!parser) {
  
      fprintf(stderr, "parser not found\n");
  
      exit(1);
  
  }
  
  
  
  c = avcodec_alloc_context3(codec);
  
  if (!c) {
  
      fprintf(stderr, "Could not allocate video codec context\n");
  
      exit(1);
  
  }
  
  
  
  /* For some codecs, such as msmpeg4 and mpeg4, width and height
  
  MUST be initialized there because this information is not
  
  available in the bitstream. */
  
  c->width = WIDTH;
  
  c->height = HEIGHT;
  
  c->pix_fmt = AV_PIX_FMT_YUV420P;
  
  c->bit_rate = 400000;
  
  c->time_base = (AVRational) { 1, 25 };
  
  
  
  /* open it */
  
  if (avcodec_open2(c, codec, NULL) < 0) {
  
      fprintf(stderr, "Could not open codec\n");
  
      exit(1);
  
  }
  
  
  
  f = fopen(filename, "rb");
  
  if (!f) {
  
      fprintf(stderr, "Could not open %s\n", filename);
  
      exit(1);
  
  }
  
  
  
  frame = av_frame_alloc();
  
  if (!frame) {
  
      fprintf(stderr, "Could not allocate video frame\n");
  
      exit(1);
  
  }
  
  frame->width = c->width;
  
  frame->height = c->height;
  
  
  
  while (!feof(f)) {
  
      /* read raw data from the input file */
  
      data_size = fread(inbuf, 1, INBUF_SIZE, f);
  
      if (!data_size)
  
          break;
  
  
  
      /* use the parser to split the data into frames */
  
      data = inbuf;
  
      while (data_size > 0) {
  
          ret = av_parser_parse2(parser, c, &pkt->data, &pkt->size,
  
                  data, data_size, AV_NOPTS_VALUE, AV_NOPTS_VALUE, AV_NOPTS_VALUE);
  
          printf("pkt size: %d\n",pkt->size);
  
          if (ret < 0) {
  
              fprintf(stderr, "Error while parsing\n");
  
              exit(1);
  
          }
  
          data += ret;
  
          data_size -= ret;
  
  
  
          if (pkt->size)
  
              decode(c, frame, pkt, outfilename);
  
      }
  
  }

• FFMPEG avformat_write_header changing my stream time_base

  12 juillet 2019, par cesarpachon

  I am muxing video using ffmpeg 2.1.3 with libavcodec 55.39.101 (forced to that version because is the one available in google-chrome PNACL port project). all my frames seems to have bad the time. they try to be rendered all at once at the beggining of the video when playing it.

  I am setting the stream time base to 1/25, but just after calling avformat_write_header, it has the value of -18082736/1.
  in each frame, when I print the stream time_base it says 1/12800, while the time_base of codec is always ok (1/25).

  console log before and after av_format_write_header :

  before avformat_write_header stream time_base: 1/25
  
  after avformat_write_header ret 0 stream time_base: -18082736/1

  the code (abreviated to keep the post short, all calls in the original version had error checking) :

  AVCodecContext *codecContext;
  
  AVCodec * codec = avcodec_find_encoder(codec_id);  
  
  myOutputStream->stream = avformat_new_stream(outputFormatContext, *codec);
  
  myOutputStream->stream->id = outputFormatContext->nb_streams-1;
  
  codecContext = myOutputStream->stream->codec;
  
  codecContext->codec_id = codec_id;
  
  codecContext->bit_rate = 400000;
  
  codecContext->width    = width;
  
  codecContext->height   = height;
  
  myOutputStream->stream->time_base = (AVRational){ 1, 25 };
  
  codecContext->time_base       = myOutputStream->stream->time_base;
  
  codecContext->gop_size      = 12; 
  
  codecContext->pix_fmt       = AV_PIX_FMT_YUV420P;
  
  AVDictionary *opt = NULL;
  
  av_dict_copy(&opt, opt_arg, 0);
  
  ret = avcodec_open2(codecContext, codec, &opt);
  
  av_dict_free(&opt);
  
  myOutputStream->frame = alloc_picture(codecContext->pix_fmt, codecContext->width, codecContext->height);
  
    myOutputStream->tmp_frame = alloc_picture(AV_PIX_FMT_YUV420P, codecContext->width, codecContext->height);
  
  
  
  //before: printing g_outputContext->stream time_base here
  
  ret = avformat_write_header(g_outputContext, &opt);
  
  //after: printing g_outputContext->stream time_base here

  If I run ffmpeg -i on the final video, I got this (why duration is zero ?) :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'test4.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2mp41
  
      encoder         : Lavf55.19.104
  
    Duration: 00:00:00.05, start: 0.000000, bitrate: 99549 kb/s
  
      Stream #0:0(und): Video: mpeg4 (Simple Profile) (mp4v / 0x7634706D), yuv420p, 800x600 [SAR 1:1 DAR 4:3], 463106 kb/s, 12800 fps, 12800 tbr, 12800 tbn, 25 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler

• H264 decoding using ffmpeg

  18 mai 2019, par Kindermann

  I’m trying to decode a video stream with ffmpeg library, that’s how I do it basically :

  void video_decode(const char *filename)
  
  {
  
      AVCodec *codec;
  
      AVCodecContext *c= NULL;
  
      int frame_count=0;
  
      FILE *f;
  
      AVFrame *frame;
  
      uint8_t inbuf[INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
  
      AVPacket avpkt;
  
      av_init_packet(&avpkt);
  
      memset(inbuf + INBUF_SIZE, 0, AV_INPUT_BUFFER_PADDING_SIZE);
  
      printf("Decoding video file...\n");
  
      /* find the h264 video decoder */
  
      codec = avcodec_find_decoder(AV_CODEC_ID_H264);
  
      c = avcodec_alloc_context3(codec);
  
      c->bit_rate = 400000;
  
      c->width = 1920;
  
      c->height = 1080;
  
  
  
      if (avcodec_open2(c, codec, NULL) < 0) {
  
          fprintf(stderr, "Could not open codec\n");
  
          exit(1);
  
      }
  
      frame = av_frame_alloc();
  
      for (;;) {
  
          avpkt.size = fread(inbuf, 1, INBUF_SIZE, f);         
  
      if (avpkt.size == 0)
  
              break;
  
          avpkt.data = inbuf;
  
          while(avpkt.size > 0){
  
  
  
          int len, got_frame;
  
              len = avcodec_decode_video2(c, frame, &got_frame, &avpkt);          
  
          if (len < 0) {
  
                  fprintf(stderr, "Errr while decding frame %d\n", frame_count);
  
                  exit (1);
  
              }
  
              if (got_frame) {
  
                  //Print out frame information..
  
          }
  
              if (avpkt.data) {
  
                  avpkt.size -= len;
  
                  avpkt.data += len;
  
              }
  
      }               
  
      }  
  
  }

  But I got the following outputs :

  Decoding video file...
  
  [h264 @ 0x303c040] decode_slice_header error
  
  [h264 @ 0x303c040] decode_slice_header error
  
  [h264 @ 0x303c040] decode_slice_header error
  
  [h264 @ 0x303c040] no frame!
  
  Errr while decding frame 0

  Obviously the initiation of codec was incomplete. Do you have experience with h264 api ? Any help would be appreciated.