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• ffmpeg undefined symbol av_frame_alloc

  19 novembre 2013, par user2930456

  So i have been trying to use the ffmpeg api's in my c project. So i first looked at some examples on the ffmpeg website and i have been trying to compile one of the examples. Im getting

      Undefined symbols for architecture x86_64:
  
      "_av_frame_alloc", referenced from:
  
      _audio_decode in ccd4jpMz.o
  
      ld: symbol(s) not found for architecture x86_64
  
      collect2: ld returned 1 exit status

  I looked at the documentation on ffmpegs website and it says av_frame_alloc is a part of libavutil
  so when i linked libavutil i got the same error. I tried linking all the libraries, i tried different orders of the libraries because i read that makes a difference. As of now I am lost and starting to lose it, any help would be appreciated. This is what i have been trying to compile the example.

      gcc -o test /Users/NahNig/Desktop/CPrograms/AudioDecoder.c $(pkg-config --libs
  
      --cflags libavutil libavformat libavcodec)

• image -> video -> image not lossless using avconv

  15 décembre 2015, par nrob

  I’m trying to test the amount of information lost with some different video codecs. I’ve got a python script which uses PyPNG to write a series of 8 bit RGB images. I then encode it using avconv, for instance

  avconv -r 1 -i ../frames/data%03d.png -c:v ffv1 -qscale:v 0 -r 1 

  outffv1.avi

  I then decode this back into pngs like so

  avconv -r 1 -i outffv1.avi -r 1 ./outffv1/frame%03d.png

  But when I compare the images before and after the video compression, they are different (mean absolute error of 15%). The thing that is confusing me is that this is true (give or take) independent of the codec.

  For instance, I get similar answers for libtheora for a range of qscale values.

  The png encoding i.e. write to png, and immediately load back in without and video compression step, is lossless.

• FFMPEG batch processing in Android

  18 août 2014, par Parikksit Bhisay

  So here’s my code :

  int iterator = 0;
  
  for(String s: pictureList){
  
  croppedPictureList.add(Constants.baseFilePath + Constants.tempNameCroppedImages + Integer.toString(iterator) + Constants.jpegFileExtension);
  
  command = "ffmpeg -i " +s+ " -vf crop=480:ih:80:0,transpose=1 " + croppedPictureList.get(0);
  
  iterator++;
  
  //Here we run the FFMPEG command, which does execute successfully!
  
  }

  croppedPictureList is a basic list of all the output files.

  the variable ’s’ is the input file path for the FFMPEG command.

  Now the problem is, if I have more than 2 images to crop, it only crops the 2nd image and saves it, the first one is lost. I don’t understand why. Are we not supposed to use batch processing like that ? Is there a different way one is supposed to batch process using FFMPEG ?

  Any help is appreciated, thanks !
  P.S. : I also checked the FFMPEG batch processing using their for loops, I’m gonna try that now and I will update if I find something. Thanks !