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• How compress images with ffmpeg till specific size threshold , and ability to restore back

  20 mars 2019, par VitalyT

  I need to reduce as much storage as i can.

  so , Lets say i have dir in file system that contains pictures (png/jpeg ,etc...) and html ,js files

  My purpose is look for media
  filenames suffix for example *.jpg, *.png, *.webm, *.ico in a folder and
  compress max till 38K.

  basically the average original images size is 170K.

  Avatar images should be under 4KB when a good size would be 2KB

  I’ve tried so far

  ffmpeg -i ~/Desktop/test123.jpeg -vframes 1 -compression_level 100  ~/Desktop/output_1623x1623.png

  but it gives me maximum 104K...

  what is the best way to compress or scaling down the images but with ability to restore with the same quality

  regards,

• RTP H263 frames to FFMPEG

  25 août 2011, par Pierluigi Cifani

  I've been trying to develop an RTP demuxed based on RFC 2190 to pass to the FFMPEG (libavcodec) H263 packets in Mode-A.

  However I can't seem to make the FFMPEG happy with the I-frames I am feeding it with. With fragmented frames (such as a large I-frame) I am rebuilding the whole frame following RFC 2190 and the "Marker" rules and passing it to the Libavcodec layer. However video looks buggy and it looks that I have to add some kind of header to the beginning of each frame before passing it to the Libavcodec layer. Errors like this are coming out all the time :

  illegal dc 128 at 0 3
  
  illegal ac vlc code at 0x3
  
  Error at MB: 69
  
  illegal ac vlc code at 4x15
  
  Error at MB: 349
  
  concealing 379 DC, 379 AC, 379 MV errors

  I have previously built an H264 over RTP demuxer and I had to add 0x00 0x00 0x00 0x01 0x21 header to every fragment of I Frame in order for it to be decoded correctly. But I can't find anywhere documentation on how to do this with H263.

  Maybe you could lend me a hand ?

  Cheers and thanks a lot

• UWP C# and Windows Runtime Component C++ Permission Denied error when opening file

  29 décembre 2020, par Surya Solanki

  I have developed a UWP app in C# which contains a Windows Runtime Component C++ project. the app allows the user to choose an mp4 file and passes this file to the c++ code, which then utilizes ffmpeg libraries to retrieve the presentation time stamps of a video file and output them to a file.

  


  the issue i'm facing is that the c++ code is not able to open the mp4 file when using the avformat_open_input function :

  


  int PTSExtraction::parse_file(Platform::String^ filename)
{
    int ret = 0;
    AVPacket pkt = { 0 };


    std::wstring fileNameW(filename->Begin());
    std::string fileNameA(fileNameW.begin(), fileNameW.end());
    const wchar_t* w_chars = fileNameW.c_str();
    src_filename = fileNameA.c_str(); 

    if (avformat_open_input(&fmt_ctx, src_filename, NULL, NULL) < 0) {
        fprintf(stderr, "Could not open source file %s\n", src_filename);
        return 1; 
    }
    // rest of code 
}


  


  the error received by avformat_open_input is Permission Denied. I cannot even open a random text file in this function by doing :

  


  ofstream output; 
output.open("output.txt");


  


  I realize there are file system permissions that are blocking the C++ component of my uwp app from opening files. here are the things i have tried so far :

  


  

  • i have enabled broadFileSystemAccess in the Package.appxmanifest (https://blogs.windows.com/windowsdeveloper/2018/05/18/console-uwp-applications-and-file-system-access/) - in the Capabilities section of the Package.appxmanifest file I've allowed access to Location, Pictures Library, and Videos Library.

  


  • I've checked the File System Privacy Settings on my computer and enabled my app to access the File System.

  


  • I've tried moving the mp4 file to various locations (Documents, Pictures Library, Videos Library) to see if the C++ component has access to these locations.

  


  • I've tried the solution from this post : Qt WinRT App cannot access file permission denied.

  


  


  None of these allow the C++ component to open any files. i would really appreciate if anyone has a solution for this problem.