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• FFMpeg avformat_write_header always returns < 0

  7 mai 2024, par gabe.roze

  We've asked a freelancer to build a video encoder with FFMPeg for iOS but there is a bug and the freelancer is no longer available. I very inexperienced in FFMpeg and video encoding and am trying to debug this error.

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  From what I understand, we're attempting to create an output file and create a header for it however, avformat_write_header is always less than zero. If I comment it out, it does not work

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  - (BOOL) writeHeaderWithError:(NSError *__autoreleasing *)error {
    AVDictionary *options = NULL;

    // Write header for output file
    int writeHeaderValue = avformat_write_header(self.formatContext, &options);
    if (writeHeaderValue < 0) {
        if (error != NULL) {
            *error = [FFUtilities errorForAVError:writeHeaderValue];
        }
        av_dict_free(&options);
        return NO;
    }
    av_dict_free(&options);
    return YES;
}


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  Below is some relevant code of how we instantiate a FFOutputFile

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      - (AVFormatContext*) formatContextForOutputPath:(NSString*)outputPath options:(NSDictionary*)options {
    AVFormatContext *outputFormatContext = NULL;
    NSString *outputFormatString = [options objectForKey:kFFmpegOutputFormatKey];

    int openOutputValue = avformat_alloc_output_context2(&outputFormatContext, NULL, [outputFormatString UTF8String], [outputPath UTF8String]);
    if (openOutputValue < 0) {
        avformat_free_context(outputFormatContext);
        return nil;
    }
    return outputFormatContext;
}

- (void) addOutputStream:(FFOutputStream*)outputStream {
    [self.streams addObject:outputStream];
}

- (id) initWithPath:(NSString *)path options:(NSDictionary *)options {
    if (self = [super initWithPath:path options:options]) {
        self.formatContext = [self formatContextForOutputPath:path options:options];
        self.streams = [NSMutableArray array];
        self.bitstreamFilters = [NSMutableSet set];
    }
    return self;
}


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• FFMpeg avformat_write_header always returns 0

  24 octobre 2015, par gabe.roze

  We’ve asked a freelancer to build a video encoder with FFMPeg for iOS but there is a bug and the freelancer is no longer available. I very inexperienced in FFMpeg and video encoding and am trying to debug this error.

  From what I understand, we’re attempting to create an output file and create a header for it however, avformat_write_header is always less than zero. If I comment it out, it does not work

  - (BOOL) writeHeaderWithError:(NSError *__autoreleasing *)error {
  
      AVDictionary *options = NULL;
  
  
  
      // Write header for output file
  
      int writeHeaderValue = avformat_write_header(self.formatContext, &options);
  
      if (writeHeaderValue < 0) {
  
          if (error != NULL) {
  
              *error = [FFUtilities errorForAVError:writeHeaderValue];
  
          }
  
          av_dict_free(&options);
  
          return NO;
  
      }
  
      av_dict_free(&options);
  
      return YES;
  
  }

  Below is some relevant code of how we instantiate a FFOutputFile

      - (AVFormatContext*) formatContextForOutputPath:(NSString*)outputPath options:(NSDictionary*)options {
  
      AVFormatContext *outputFormatContext = NULL;
  
      NSString *outputFormatString = [options objectForKey:kFFmpegOutputFormatKey];
  
  
  
      int openOutputValue = avformat_alloc_output_context2(&outputFormatContext, NULL, [outputFormatString UTF8String], [outputPath UTF8String]);
  
      if (openOutputValue < 0) {
  
          avformat_free_context(outputFormatContext);
  
          return nil;
  
      }
  
      return outputFormatContext;
  
  }
  
  
  
  - (void) addOutputStream:(FFOutputStream*)outputStream {
  
      [self.streams addObject:outputStream];
  
  }
  
  
  
  - (id) initWithPath:(NSString *)path options:(NSDictionary *)options {
  
      if (self = [super initWithPath:path options:options]) {
  
          self.formatContext = [self formatContextForOutputPath:path options:options];
  
          self.streams = [NSMutableArray array];
  
          self.bitstreamFilters = [NSMutableSet set];
  
      }
  
      return self;
  
  }

• 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/