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• "fixing" RTL texts from logical to visual, before embedding in video as subtitles with ffmpeg

  13 mai 2024, par Berry Tsakala

  I'm searching for the correct way to pre-process my subtitles files before hard-coding them into video clips.

  


  Currently, ffmpeg does not process RTL (right-to-left) languges properly ; I have detailed the problem here :
https://superuser.com/questions/1679536/how-to-embed-rtl-subtitles-in-a-video-hebrew-arabic-with-the-correct-lan

  


  However, there could be 2 programmatic solutions :

  


  

  1. adding certain unicode control characters can fix (or partially fix) the text, which is then fed into ffmpeg, giving good results.

  


  


  

  • character 0x200F at the end of a hebrew clause, after punctuation

  


  • character 0x202B, I haven't yet learned its usage.

  


  


  

  2. I can edit the text so that it will produce the correct results on ffmpeg.
But that requires smart BiDi algorithm.

  


  


  Do you know how to preprocess such text ?

  


  (this is NOT an encoding question. It is about RTL/LTR algorithm to use.)

  


  Thank you

  


• While ffmpeg convers via php website doesnt work

  29 octobre 2013, par Xenos Trojanowicz

  So im using

                  if ($success_msg) 
  
              {
  
                  $tmp_parts = explode('.', $file['name']);
  
                  $ext = array_pop($tmp_parts);
  
                  $ext = strtolower($ext);
  
                  if($ext == "avi" && $convert_avi == true)
  
                      {
  
                          $convert_source = _VIDEOS_DIR_PATH.$new_name;
  
                          $conv_name = substr(md5($file['name'].rand(1,888)), 2, 10).".mp4";
  
                          $converted_file  = _VIDEOS_DIR_PATH.$conv_name;
  
                          $ffmpeg_command = 'ffmpeg -i '.$convert_source.'-acodec libfaac -vcodec libx264 -s 1280x720 -ar 44100 -async 44100 -r 29.970 -ac 2 -qscale 5 '.$converted_file;
  
                          echo exec($ffmpeg_command);
  
                          $sql = "UPDATE pm_temp SET url = '".$conv_name."' WHERE url = '".$new_name."' LIMIT 1";
  
                          $result = @mysql_query($sql);
  
                          unlink($convert_source);    
  
                      }
  
                  echo $success_msg;
  
              }

  This code to convert videos from avi to mp4 but i have another big issue when i upload big file let say 170 mb it converts about 25 minutes or so and while it converts website doesnt work for me.

  NOW I KNOW WHY WEBSITE DOESNT WORK :

  • its only for me becose system doesnt open extra slot to enter to website while it converts
  • i know how to solve this problem with cronjob but im afraid that if something goes wrong it will be biggest fail i ever had

  so im hopping that u guys will suggest something smart and easy to deal with this issue

• Is it safe to set AVPacket::duration to one ?

  9 septembre 2021, par Vivekanand V

  I am new to the world of programming of multimedia applications. I just managed to get a hold of FFMPEG's libraries to perform video encoding and decoding in C/C++ and I feel that I have a lack of understanding in many aspects of the whole process.

  


  My application converts an RGB24 array referenced by unsigned char* to a AVFrame, and encodes it to a video file.

  


  During initialization, I set the time base in codec context to 1/fps, where fps is the frame rate.

  


  AVStream::time_base is also set to the same value.

  


  Is there is a mathematical relationship between these time bases to AV_TIME_BASE constant ?

  


  How should AVFrame::pts be set. Here I am just incrementing by one for every encoding operation.

  


  How should AVPacket::duration be set, before calling av_interleaved_write_frame ?

  


  What is the significance of AVPacket::pts and AVPacket::dts ?