Recherche avancée

Sur d’autres sites (7451)

• c++ avformat_open_input returns empty codec, width and height

  27 février 2019, par Victor Akhlynin

  I haven’t ever used ffmpeg on my own laptop. All’s ok at work, but here I met an ugly problem : library works but helpless :)
  Ubuntu 18.04, ffmpeg 4.1 (downloaded sources, ./configure, make, sudo make install), it seems to be ok.

  Application returns :
  File /home/ahlininv/Desktop/video_example.mp4 is encodec with ’’ codec, w = 0, h = 0

  I ran it under debugger. If I set format to zero, pointer changes after calling avformat_open_input(&format, file, 0, &dict), so it works and maybe works correct.

  Maybe it plays any role that compiler says that av_register_all, avcodec_register_all are deprecated, but I thought it’s not significant problem.

  I tried to change version of ffmpeg (tried to install it with apt-get, version 3.somenumber is available), nothing changed.

  I tried to run another video file (.avi), nothing changed, too.

  Guys, help=) How to this file’s info correctly ?

  main.cpp :

  #include "filereader.h"
  
  
  
  int main(int argc, char** argv) {
  
  
  
      std::string filename = "/home/ahlininv/Desktop/video_example.mp4";
  
  
  
      std::string codec;
  
      int w, h;
  
      bool open_ok = get_file_info(filename.c_str(), codec, w, h);
  
      if (!open_ok) {
  
          std::cout << "Failed to open file" << "\n";
  
          return 1;
  
      }
  
  
  
      std::cout << "File " << filename << " is encoded with '" << codec << "' codec, w = " << w << ", h = " << h << "\n";
  
  
  
      return 0;
  
  }

  filereader.h :

  #ifndef FILEREADER_H
  
  #define FILEREADER_H
  
  
  
  #include <string>
  
  #include <iostream>
  
  
  
  extern "C" {
  
  #ifndef __STDC_CONSTANT_MACROS
  
  #define __STDC_CONSTANT_MACROS
  
  #endif
  
  #include "libavcodec/avcodec.h"
  
  #include <libavformat></libavformat>avformat.h>
  
  #include <libavutil></libavutil>avutil.h>
  
  }
  
  
  
  bool get_file_info(const char* file, std::string&amp; codec, int&amp; w, int&amp; h);
  
  
  
  #endif // FILEREADER_H
  
  </iostream></string>

  filereader.cpp

  #include "filereader.h"
  
  
  
  
  
  bool get_file_info(const char* file, std::string& codec, int& w, int& h)
  
  {
  
      codec = "";
  
      w = h = 0;
  
  
  
      av_register_all();
  
      avcodec_register_all();
  
  
  
      AVDictionary* dict = 0;
  
      AVFormatContext* format = avformat_alloc_context();
  
  
  
      char errbuf[256];
  
      int r = avformat_open_input(&format, file, 0, &dict);
  
      if (r!=0){
  
          av_strerror(r, errbuf, sizeof(errbuf));
  
          std::cout << "avformat_open_input error: " << errbuf << "\n";
  
      }
  
  
  
      if (r == AVERROR(EIO) || r == AVERROR(ENOEXEC) || !format)
  
          return false;
  
  
  
      for (size_t c = 0; c < format->nb_streams; ++c)
  
      {
  
          if (format->streams[c]->codecpar && format->streams[c]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
  
          {
  
              if (format->streams[c]->codecpar->codec_id != AV_CODEC_ID_NONE &&
  
                      format->streams[c]->codecpar->codec_id != AV_CODEC_ID_RAWVIDEO)
  
              {
  
                  w = format->streams[c]->codecpar->width;
  
                  h = format->streams[c]->codecpar->height;
  
                  codec = avcodec_get_name(format->streams[c]->codecpar->codec_id);
  
              }
  
          }
  
      }
  
      avformat_close_input(&format);
  
      return true;
  
  }

  Compile :

  g++ -o filereader main.cpp filereader.cpp -lavutil -lavformat -lavcodec -lavdevice -lz -lm -pthread -lswresample -lm -lz -I /usr/local/include/ -Wl,-rpath /usr/lib/x86_64-linux-gnu/

• lavc/vvc : Read subpic ID when only one subpicture is present

  25 février 2024, par Frank Plowman

  lavc/vvc : Read subpic ID when only one subpicture is present
  Previously, the following syntax elements were not read in the case
  
  sps_num_subpics_minus is 0 :
  
  * sps_subpic_id_len_minus1
  
  * sps_subpic_id_mapping_explicitly_signalled_flag
  
  * sps_subpic_id_mapping_present_flag
  
  * sps_subpic_id[i]
  
  This was causing failures to decode bitstreams, for example the DVB's
  
  "VVC HDR UHDTV1 OpenGOP 3840x2160 50fps HLG10 PiP" V&V bitstream.
  Patch fixes this by moving the reads for these syntax elements out a
  
  scope.
  Signed-off-by : Frank Plowman <post@frankplowman.com>
  
  Signed-off-by : James Almer <jamrial@gmail.com>
  

  • [DH] libavcodec/cbs_h266_syntax_template.c

• Read metadata from a MPEG file in encoded domain

  13 juin 2017, par Sanduni Wickramasinghe

  I’m trying to extract information from an MPEG video in an encoded domain. I use

  avformat_open_input(&s, url, NULL, &options)

  to read the data packet. Is there a possible way of reading meta data from the file before decoding ?

  I can get information such as size and duration which are available in AVPacket structure. I want to get information other than that.