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• FFmpeg output doesn't match source

  10 octobre 2019, par Patrick O'Brien

  I can’t seem to match the ffmpeg output with the source exr. Linking to the source exr and movie here : https://www.dropbox.com/sh/mc19q5m9bf17goi/AAAfs4o_vxnAePIZVrOBrEZRa?dl=0. I’ve tried a lot of flags, the closest seems to be this :

  C :\PyAniTools\apps\pyShoot\ffmpeg\bin\ffmpeg.exe -apply_trc iec61966_2_1 -i C :\Users\Patrick\Downloads\050_020_render_layer\char_back\char_back.1062.exr -vcodec libx264 -pix_fmt yuv420p -preset slow -crf 18 -r 25 C :\Users\Patrick\Downloads\050_020_render_layer\char_back\char_back.1062.mp4

  It’s still different though. Source exr :
  

  It’s hard to tell probably but parts of the image get darker :
  

  Any help would be greatly appreciated, I’ve been trying things for days. Thanks,
  Patrick

• Can't compile C library with C++ code using g++

  13 novembre 2019, par shayst

  I’m trying to create a C++ program that embeds FFMPEG functionality.
  To do that I took one FFMPEG example and recompiled it as is using g++ (only adding extern "C" where needed).
  Compilation is successful, but linking fails for undefined symbols.

  cc -I/usr/include/x86_64-linux-gnu -Wall -g -fPIC  -c -o bin/decode_video.o decode_video.cpp
  
  
  
  cc -Wl,--export-dynamic,--no-undefined -L /usr/lib/x86_64-linux-gnu/ -shared -lavdevice -lavutil -lavcodec  bin/decode_video.o -o decode_video.so
  
  
  
  bin/decode_video.o: In function `decode(AVCodecContext*, AVFrame*, AVPacket*, char const*)':
  
  /home/admin1/ffmpeg_examples/decode_video.cpp:60: undefined reference to `avcodec_send_packet'
  
  /home/admin1/ffmpeg_examples/decode_video.cpp:67: undefined reference to `avcodec_receive_frame'
  
  bin/decode_video.o: In function `main':
  
  /home/admin1/ffmpeg_examples/decode_video.cpp:108: undefined reference to `av_packet_alloc'
  
  /home/admin1/ffmpeg_examples/decode_video.cpp:116: undefined reference to `avcodec_find_decoder'
  
  /home/admin1/ffmpeg_examples/decode_video.cpp:122: undefined reference to `av_parser_init'
  
  /home/admin1/ffmpeg_examples/decode_video.cpp:128: undefined reference to `avcodec_alloc_context3'
  
  /home/admin1/ffmpeg_examples/decode_video.cpp:139: undefined reference to `avcodec_open2'
  
  /home/admin1/ffmpeg_examples/decode_video.cpp:150: undefined reference to `av_frame_alloc'
  
  /home/admin1/ffmpeg_examples/decode_video.cpp:165: undefined reference to `av_parser_parse2'
  
  /home/admin1/ffmpeg_examples/decode_video.cpp:184: undefined reference to `av_parser_close'
  
  /home/admin1/ffmpeg_examples/decode_video.cpp:185: undefined reference to `avcodec_free_context'
  
  /home/admin1/ffmpeg_examples/decode_video.cpp:186: undefined reference to `av_frame_free'
  
  /home/admin1/ffmpeg_examples/decode_video.cpp:187: undefined reference to `av_packet_free'

  checking nm I see that there’s no name mangling in action so extern C seems to work well :

  nm bin/decode_video.o 
  
  
  
                   U avcodec_alloc_context3
  
                   U avcodec_find_decoder
  
                   U avcodec_free_context
  
                   U avcodec_open2
  
                   U avcodec_receive_frame
  
                   U avcodec_send_packet
  
                   U av_frame_alloc
  
                   U av_frame_free
  
                   U av_packet_alloc
  
                   U av_packet_free
  
                   U av_parser_close
  
                   U av_parser_init
  
                   U av_parser_parse2
  
                   U exit
  
                   U fclose
  
                   U feof
  
                   U fflush
  
                   U fopen
  
                   U fprintf
  
                   U fread
  
                   U fwrite
  
                   U _GLOBAL_OFFSET_TABLE_
  
  000000000000026f T main
  
                   U memset
  
                   U printf
  
                   U snprintf
  
                   U __stack_chk_fail
  
                   U stderr
  
                   U stdout
  
  00000000000000a3 t _ZL6decodeP14AVCodecContextP7AVFrameP8AVPacketPKc
  
  0000000000000000 t _ZL8pgm_savePhiiiPc

  checking the library, for one of the ’missing’ symbols, I can see it is implemented

  nm /usr/lib/x86_64-linux-gnu/libavcodec.a | grep avcodec_send_packet
  
  
  
  00000000000033e0 T avcodec_send_packet
  
                   U avcodec_send_packet

  When compiling in C it works perfectly (without extern C of course) which makes me wonder what am I missing ?

  Below find FFMPEG example code for reference (decode_video.cpp) :

  #include 
  
  #include 
  
  #include 
  
  
  
  extern "C"
  
  {
  
  #include <libavcodec></libavcodec>avcodec.h>
  
  }
  
  
  
  #define INBUF_SIZE 4096
  
  
  
  static void pgm_save(unsigned char *buf, int wrap, int xsize, int ysize,
  
                       char *filename)
  
  {
  
      FILE *f;
  
      int i;
  
  
  
      f = fopen(filename,"w");
  
      fprintf(f, "P5\n%d %d\n%d\n", xsize, ysize, 255);
  
      for (i = 0; i &lt; ysize; i++)
  
          fwrite(buf + i * wrap, 1, xsize, f);
  
      fclose(f);
  
  }
  
  
  
  static void decode(AVCodecContext *dec_ctx, AVFrame *frame, AVPacket *pkt,
  
                     const char *filename)
  
  {
  
      char buf[1024];
  
      int ret;
  
  
  
      ret = avcodec_send_packet(dec_ctx, pkt);
  
      if (ret &lt; 0) {
  
          fprintf(stderr, "Error sending a packet for decoding\n");
  
          exit(1);
  
      }
  
  
  
      while (ret >= 0) {
  
          ret = avcodec_receive_frame(dec_ctx, frame);
  
          if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
  
              return;
  
          else if (ret &lt; 0) {
  
              fprintf(stderr, "Error during decoding\n");
  
              exit(1);
  
          }
  
  
  
          printf("saving frame %3d\n", dec_ctx->frame_number);
  
          fflush(stdout);
  
  
  
          /* the picture is allocated by the decoder. no need to
  
             free it */
  
          snprintf(buf, sizeof(buf), "%s-%d", filename, dec_ctx->frame_number);
  
          pgm_save(frame->data[0], frame->linesize[0],
  
                   frame->width, frame->height, buf);
  
      }
  
  }
  
  
  
  int main(int argc, char **argv)
  
  {
  
      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;
  
  
  
      if (argc &lt;= 2) {
  
          fprintf(stderr, "Usage: %s <input file="file" /> <output file="file">\n"
  
                  "And check your input file is encoded by mpeg1video please.\n", argv[0]);
  
          exit(0);
  
      }
  
      filename    = argv[1];
  
      outfilename = argv[2];
  
  
  
      pkt = av_packet_alloc();
  
      if (!pkt)
  
          exit(1);
  
  
  
      /* 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_MPEG1VIDEO);
  
      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. */
  
  
  
      /* open it */
  
      if (avcodec_open2(c, codec, NULL) &lt; 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);
  
      }
  
  
  
      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, &amp;pkt->data, &amp;pkt->size,
  
                                     data, data_size, AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);
  
              if (ret &lt; 0) {
  
                  fprintf(stderr, "Error while parsing\n");
  
                  exit(1);
  
              }
  
              data      += ret;
  
              data_size -= ret;
  
  
  
              if (pkt->size)
  
                  decode(c, frame, pkt, outfilename);
  
          }
  
      }
  
  
  
      /* flush the decoder */
  
      decode(c, frame, NULL, outfilename);
  
  
  
      fclose(f);
  
  
  
      av_parser_close(parser);
  
      avcodec_free_context(&amp;c);
  
      av_frame_free(&amp;frame);
  
      av_packet_free(&amp;pkt);
  
  
  
      return 0;
  
  }
  
  </output>

• avcodec/avcodec : Adapt the doc of av_bsf_send_packet to match its actual implementation.

  14 novembre 2019, par Andreas Rheinhardt

  avcodec/avcodec : Adapt the doc of av_bsf_send_packet to match its actual implementation.
  Explicitly allowing empty packets to signal flushing helps getting rid
  
  of special cases. It does not hinder the ability to send i.e.
  
  timing-only packets, because one can send packets with zero size and
  
  pkt->data set.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  
  Signed-off-by : James Almer <jamrial@gmail.com>
  

  • [DH] libavcodec/avcodec.h