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• FFmpeg (sharpFFmpeg) decoding - Protected memory error

  25 août 2011, par mazharenko.a

  I'm trying to use C# binding of FFmpeg library calling SharpFFmpeg to decode H264 video stream that I receive by RTP. I think I correctly decapsulate NALUs from RTP-packets, but I can't decode complete frames. Function avcodec_decode_video calling throws an AccessViolationException (Attempted to read or write protected memory).
  Here are some code lines :

      //buf is a byte array containing encoded frame
  
      int success;
  
      FFmpeg.avcodec_init();
  
      FFmpeg.avcodec_register_all();
  
      IntPtr codec = FFmpeg.avcodec_find_decoder(FFmpeg.CodecID.CODEC_ID_H264);
  
      IntPtr codecCont = FFmpeg.avcodec_alloc_context(); //AVCodecContext
  
      FFmpeg.avcodec_open(codecCont, codec);
  
      IntPtr frame = FFmpeg.avcodec_alloc_frame();  //AVFrame
  
      FFmpeg.avcodec_decode_video(codecCont, frame, ref success, (IntPtr)buf[0], buf.Length); //exception

  Function has been imported as follows :

      [DllImport("avcodec.dll", CallingConvention = CallingConvention.Cdecl), SuppressUnmanagedCodeSecurity]
  
      public unsafe static extern int avcodec_decode_video(IntPtr pAVCodecContext, IntPtr pAVFrame, ref int got_picture_ptr, IntPtr buf, int buf_size);

  Unfortunately, I don't know what do I have to do with the codecCont. Somebody wrote that it is needed to fill this structure by AVCDCR using session description received by RTSP. But I don't know which field(s) store this record.
  I'll be glad for any help.
  P.S. Excuse me for my English

• Programmatically capture X11 region with ffmpeg in C/whatever

  26 février 2013, par zw0rk

  There is an input format option to ffmpeg — x11grab which allows one to capture specified region and output it to file/stream. I'm trying to do the same thing programmatically, but i haven't found any non-basic tutorials/reference for ffmpeg API.

  I wonder, how it is possible to open x11 region with avformat_input_file or something like this. Or should i do it with XCopyArea/etc ?

  (Any programming language will satisfy)

• Deobfuscation Redux : JavaScript

  20 juin 2011, par Multimedia Mike — Reverse Engineering, deobfuscation, javascript, programming

  Google recently released version 12 of their Chrome browser. This version adds a new feature that automatically allows deobfuscating obfuscated JavaScript source code.

  Before :

  
  
  

  After :

  
  
  

  As a reverse engineering purist, I was a bit annoyed. Not at the feature, just the naming. This is clearly code beautification but not necessarily deobfuscation. The real obfuscation comes not from removing whitespace but from renaming variable and function names to terse 1- and 2-letter identifiers. True automated deobfuscation — which entails recovering the original variable and function identifiers as well as source code comments — is basically impossible.

  Still, it makes me wonder if there is any interest in a JavaScript deobfuscator that operates similar to my Java deobfuscator which was one of the first things I published on this blog. The general idea is automatically replace function names with random English verbs (since functions correspond to actions) and variable names with random animal names (I decided "English nouns" encompassed too broad a category of words). I suspect the day that someone releases a proprietary multimedia codec in a pure (though obfuscated) JavaScript format is that day that I will try to accomplish this, if it hasn’t been done already.

  See also :

  • Success on the Java De-obfuscation Front