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• Updated license link and added package information.

  15 décembre 2011, par Sebastian Tschan

  .gitignore m README.md m application.js m gae-go/app/main.go m gae-python/main.py m index.html m jquery.fileupload-ui.css m jquery.fileupload-ui.js m jquery.fileupload.js m jquery.iframe-transport.js m jquery.postmessage-transport.js m jquery.xdr-transport.js + package.json m php/index.php m (...)

• The Fastest Way To Learn Assembly Language

  4 septembre 2011, par Multimedia Mike — Programming

  I saw an old StackOverflow thread linked from Hacker News asking how to whether it’s worthwhile to learn assembly language and how to go about doing so. I’d like to take a stab at the last question.

  The fastest way to learn an assembly language is to reverse engineer something. Seriously, start with something that you know (like a C program that you wrote yourself) and take it apart. The good news is that assembly language is very simple and you will get a lot of practice in a short amount of time with RE.

  So here’s how you do it :

  • Take a simple program in C and build it with your tool chain, whether GNU gcc on Linux, Xcode on Mac, or MSVC on Windows. Also, make sure to turn on debugging symbols during compilation (this will help annotate the disassembly).
  • On Linux, use objdump : objdump -d program_binary
  • On Mac, use otool : otool -tV program_binary
  • On Windows : I admit, I’m a bit fuzzy on this one– I’m quite certain there’s a standard MSVC tool that prints the assembly listing.

  Anyway, look at the disassembled code and find the main() function. Work from there. Whatever the first instruction is, look it up on Google. You’ll likely find various CPU manuals that will explain the simple operation of the instruction. Look up the next unfamiliar instruction, then the next. Trust me, you’ll become an ASM expert in no time.

  Good luck !

• FFMPEG Undefined Reference to 'avcodoec_open2' in C++

  12 avril 2012, par ALM865

  I have an error when compiling one of my C++ programs after updating the FFMPEG library from 0.8 to 'ffmpeg version git-2012-04-12-277f20c'

  The error I get when I make my program is as follows :

  -------- begin --------
  
  Linking: Analysing_Server
  
  ./source/Encoding_Thread.o: In function `CEncoding_Thread::do_work()':
  
  /home/Analyser/source/Encoding_Thread.cpp:155: undefined reference to `avcodec_open2'
  
  collect2: ld returned 1 exit status
  
  make: *** [Analysing_Server] Error 1

  The relevant lines of my Make file is similar to running g++ as below :

  g++ test2.cpp -lavformat -lavcodec -lavutil -D__STDC_CONSTANT_MACROS

  A stripped down version of my relevant CPP code that throws the error is :

  #include 
  
  #include  
  
  
  
  #define LOG_OUT_STREAM_BUFF_SIZE  200000
  
  
  
  
  
  extern "C"  {
  
    /* The ffmpeg library is completely written in C, so we need to tell the C++ compiler that so it links correctly. */
  
    #include "stdint.h"
  
    #include "libavcodec/avcodec.h"
  
    #include "libavutil/mathematics.h"
  
    #include "libswscale/swscale.h"
  
    #include "libavfilter/avfilter.h"
  
  
  
    int avcodec_open2(AVCodecContext *avctx, AVCodec *codec, AVDictionary **options);
  
    int avcodec_encode_video2(AVCodecContext *avctx, AVPacket *avpkt, const AVFrame *frame, int *got_packet_ptr);
  
  }
  
  
  
  uint8_t m_outbuf[2][LOG_OUT_STREAM_BUFF_SIZE];
  
  unsigned int m_out_size[2];
  
  unsigned int m_OutBuffer_ID[2];
  
  unsigned int m_Buffer_ID; /* This is just a uniqueish stamp we give to each buffer so we can tell when they change.. */
  
  
  
  AVCodecContext * m_CodecContex;
  
  AVCodec * m_codec;
  
  struct SwsContext *m_img_convert_ctx;
  
  
  
  unsigned char* m_DataBuff;
  
  
  
  int Output_Width, Output_Height;
  
  int Output_Bitrate;
  
  
  
  
  
  int main(void) {
  
    //New version of FFMPEG calls this in avcodec_register_all
  
    //avcodec_init();
  
  
  
    /* register all the codecs */
  
    avcodec_register_all();
  
  
  
    /* Initalise the encoder */
  
    m_codec = avcodec_find_encoder(CODEC_ID_MP2);
  
  
  
    if (!m_codec) {
  
      printf("Encoding codec not found\n");
  
    }
  
  
  
    /* init the pointers.. */
  
    m_CodecContex = NULL;
  
  
  
    /* Default values.. */
  
    Output_Width = 1600;
  
    Output_Height = 1200;
  
    Output_Bitrate = 600000;
  
  
  
    /* Create/setup the Codec details.. */
  
    //Changed to work with new FFMPEG
  
    m_CodecContex = avcodec_alloc_context3(m_codec);
  
    avcodec_get_context_defaults3(m_CodecContex, m_codec);
  
  
  
    /* put sample parameters */
  
    m_CodecContex->bit_rate = Output_Bitrate;
  
    /* resolution must be a multiple of two */
  
  
  
    m_CodecContex->width = Output_Width;
  
    m_CodecContex->height = Output_Height;
  
    /* frames per second */
  
    m_CodecContex->time_base= (AVRational){1,25};
  
  
  
    m_CodecContex->gop_size = 10; /* emit one intra frame every ten frames */
  
    m_CodecContex->max_b_frames=1;
  
    m_CodecContex->pix_fmt = PIX_FMT_YUV420P; /* must be YUV for encoding.. */
  
  
  
  
  
    AVDictionary * RetunedAVDic;
  
  
  
    /* open it */
  
    //Changed to work with new FFMPEG
  
    if (avcodec_open2(m_CodecContex, m_codec, &RetunedAVDic) < 0) {
  
        printf("could not open codec");
  
    }
  
  }

  Unfortunately the example under 'doc/examples/decoding_encoding.c' that comes with FFMPEG no longer works because all the functions that it uses are now depreciated. My code is based on the example code and worked fine with FFMPEG 0.8 but does not compile with the newest version of FFMPEG. I have changed some of the depreciated functions to their newer versions but it still doesn't compile.

  Does anyone know why I am getting this error ? or does anyone have a link to an example like 'doc/examples/decoding_encoding.c' using the newest version of FFMPEG ?