libavcodec ve libavformat ile video bilgilerini öğrenmek

libavcodec,libavformat Â free software/open source LGPL-lisanslı ffmpeg tarafından kullanılan codec çözme / işleme kütüphanesidir.

Ubuntu – Debian altında örnek kodu derleyebilmek için gerekli paketler :

$ sudo apt-get install libavcodec-dev libavformat-dev

Derlemek için :

g++ avf.cpp -I/usr/include/libavcodec -I/usr/include/libavformat -lavformat -lavcodec -L/usr/lib/libavformat.so -L/usr/lib/libavcodec.so -o avf

Örnek Kullanım :

./avf test.mp4

Ã‡ıktı :

Video codec Â Â Â : mp42

Width Â Â Â Â : 1920

Height Â Â Â Â : 1080

DurationÂ Â Â : 300

Audio codec Â Â : aac

Audio channels Â Â : 2

Audio samplerate Â : 44100

Audio bitrate Â Â : 128

#ifndef INT64_C
#define INT64_C(c) (c ## LL)
#define UINT64_C(c) (c ## ULL)
#endif

extern "C" {
#include &lt;avcodec.h&gt;
#include &lt;avformat.h&gt;
}

#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
#include &lt;iostream&gt;

//g++ avf.cpp -I/usr/include/libavcodec -I/usr/include/libavformat -lavformat -lavcodec -L/usr/lib/libavformat.so -L/usr/lib/libavcodec.so -o avf

using namespace std;

int main(int argc, char *argv[])
{
	av_log_set_level(0);
	av_register_all();
	AVFormatContext *pFormatCtx;
	const char      *filename=argv[1];

	// Open video file
	if(av_open_input_file(&amp;pFormatCtx, filename, NULL, 0, NULL)!=0)
	{
	   cout &lt; &lt; "can't open file" &lt;&lt; endl;
	   exit(-1);
	}	

	// Retrieve stream information
	if(av_find_stream_info(pFormatCtx)&lt;0)
	{
	  cout &lt;&lt; "can't get stream info" &lt;&lt; endl; 	  exit(-1); 	} 	//dump_format(pFormatCtx, 0, filename, false); 	int            i, videoStream; 	AVCodecContext *pCodecCtx; //http://ffmpeg.org/doxygen/0.6/structAVCodecContext.html 	AVCodecContext *pCodecCtx2; 	 	pCodecCtx=pFormatCtx-&gt;streams[0]-&gt;codec;
	pCodecCtx2=pFormatCtx-&gt;streams[1]-&gt;codec;

	AVCodec* vCodec;//http://ffmpeg.org/doxygen/0.6/structAVCodec.html
	AVCodec* aCodec;
	vCodec=avcodec_find_decoder(pCodecCtx-&gt;codec_id);
	aCodec=avcodec_find_decoder(pCodecCtx2-&gt;codec_id);

	cout &lt; &lt; "Video codec       : " &lt;&lt; vCodec-&gt;name &lt; &lt; endl;
	cout &lt;&lt; "Width    	  : " &lt;&lt; pCodecCtx-&gt;width &lt; &lt; endl;
	cout &lt;&lt; "Height   	  : " &lt;&lt; pCodecCtx-&gt;height &lt; &lt; endl;
	cout &lt;&lt; "Duration 	  : " &lt;&lt; pFormatCtx-&gt;duration &lt; &lt; endl;
	//cout &lt;&lt; "codec id	  : " &lt;&lt; (int)pCodecCtx2 &lt;&lt; endl;
	cout &lt;&lt; "Audio codec	  : " &lt;&lt; aCodec-&gt;name &lt; &lt; endl;
	cout &lt;&lt; "Audio channels    : " &lt;&lt; pCodecCtx2-&gt;channels &lt; &lt; endl;
	cout &lt;&lt; "Audio samplerate  : " &lt;&lt;  pCodecCtx2-&gt;sample_rate &lt; &lt; endl;
	cout &lt;&lt; "Audio bitrate     : " &lt;&lt;  pCodecCtx2-&gt;bit_rate &lt; &lt; endl;

	avcodec_close(pCodecCtx);
	avcodec_close(pCodecCtx2);

	av_close_input_file(pFormatCtx);
	return 0;
}

#ifndef INT64_C

#define INT64_C(c) (c ## LL)

#define UINT64_C(c) (c ## ULL)

#endif

extern "C" {

#include <avcodec.h>

#include <avformat.h>

}

#include <stdio.h>

#include <stdlib.h>

#include <iostream>

//g++ avf.cpp -I/usr/include/libavcodec -I/usr/include/libavformat -lavformat -lavcodec -L/usr/lib/libavformat.so -L/usr/lib/libavcodec.so -o avf

using namespace std;

int main(int argc, char *argv[])

{

av_log_set_level(0);

av_register_all();

AVFormatContext *pFormatCtx;

const char *filename=argv[1];

// Open video file

if(av_open_input_file(&pFormatCtx, filename, NULL, 0, NULL)!=0)

{

cout < < "can't open file" << endl;

exit(-1);

}

// Retrieve stream information

if(av_find_stream_info(pFormatCtx)<0)

{

cout << "can't get stream info" << endl; exit(-1); } //dump_format(pFormatCtx, 0, filename, false); int i, videoStream; AVCodecContext *pCodecCtx; //http://ffmpeg.org/doxygen/0.6/structAVCodecContext.html AVCodecContext *pCodecCtx2; pCodecCtx=pFormatCtx->streams[0]->codec;

pCodecCtx2=pFormatCtx->streams[1]->codec;

AVCodec* vCodec;//http://ffmpeg.org/doxygen/0.6/structAVCodec.html

AVCodec* aCodec;

vCodec=avcodec_find_decoder(pCodecCtx->codec_id);

aCodec=avcodec_find_decoder(pCodecCtx2->codec_id);

cout < < "Video codec : " << vCodec->name < < endl;

cout << "Width : " << pCodecCtx->width < < endl;

cout << "Height : " << pCodecCtx->height < < endl;

cout << "Duration : " << pFormatCtx->duration < < endl;

//cout << "codec id : " << (int)pCodecCtx2 << endl;

cout << "Audio codec : " << aCodec->name < < endl;

cout << "Audio channels : " << pCodecCtx2->channels < < endl;

cout << "Audio samplerate : " << pCodecCtx2->sample_rate < < endl;

cout << "Audio bitrate : " << pCodecCtx2->bit_rate < < endl;

avcodec_close(pCodecCtx);

avcodec_close(pCodecCtx2);

av_close_input_file(pFormatCtx);

return 0;

}

Örnek kod

Vigenere Åžifrelemesi (Vigenere Cipher)

Vigenere Åžifreleme tekniği, 16. yüzyılda Fransa 3. Henry Kraliyet üyesi Blaise de Vigenere tarafından bulunmuştur. Burada birbiri yerine kullanılacak harfleri belirlemek için Vigenere Tablosu kullanılır. İngiliz Alfabesi için Tablo 26×26 boyutlarındadır.

Åžifreleme bir anahtar kullanılarak yapılır ve anahtardaki harfler tablonun başlık satırında aranır. Buna karşılık düz metindeki harf tablonun başlık sütununda aranır. Bulunan satır ve sütunun kesiştiği yerdeki harf, düz metindeki harfin yerine konarak şifreleme işlemi gerçekleştirilir.

Åžöyle bir örnek verebiliriz:

Anahtar kelime :LEMONLEMONLE

Düz Metin :ATTACKATDAWN

Åžifreli Metin :LXFOPVEFRNHR

Åžifreli metindeki tekrar eden desenler bulunup, bunlar arasındaki uzaklık hesaplanarak anahtar uzunluğu belirlenebilir. Örneğin anahtar uzunluğu N olarak bulunursa, N tane (Anahtardaki harfler birbirinden farklı ise) tek alfabeli Yerine-Koyma şifreleme tekniği kullanıldığı anlaşılır. Bu aşamada artık her bir tek alfabeli şifreli metne, ayrı ayrı, düz metin harflerinin frekans karakteristiklerini kullanan bir saldırı gerçekleştirilebilir.

Vigenere Åžifreleme tekniği ilk kez 1854’de Charles Babbage tarafından kırılmıştır. Charles’ın kullandığı frekans analizi yaklaşımı, kripto analistlere bir araç olmuştur.

Visual C++ 6 Proje dosyaları – Gozat

C# – Gözat

Kaynaklar :

http://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher
http://ab.org.tr/ab05/tammetin/22.doc

write in C :)

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