How to overwrite i-frames of a video?

Question

I want to destroy all the i-frames of the video. In doing this, I want to check if only the i-frames of the video are encrypted enough to make it impossible. How can i do this? Only deleting them and re-compressing the video will not be the same as rewriting an i-frame in a stream without recalculating b-frames, etc.

Answer 1

Using libavformat (library from ffmpeg), you can demultiplex the video into packages that represent a single frame. You can then encrypt the data in packets marked as key frames. Finally, you can reconfigure the video to a new file. There is a good libavformat / libavcodec tutorial here . You will not need to actually decode / encode frames, because I assume that you just want to encrypt the compressed data. In this case, after reading AVPacket, just encrypt your data if it is a key frame ( packet->flags & PKT_FLAG_KEY). Then you have to write the packages to a new file.

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ffmpeg -i filename -an -vcodec copy -f rawvideo output_filename

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#include <iostream>
using namespace std;
//...

//...
ifstream ifs("filename", ios::in | ios::binary);
//initialize buffer to 0xffffffff
unsigned char buffer[4] = {0xff, 0xff, 0xff, 0xff};
while(!ifs.eof())
{
    //Shift to make space for new read.
    buffer[0] = buffer[1];
    buffer[1] = buffer[2];
    buffer[2] = buffer[3];

    //read next byte from file
    buffer[3] = ifs.get();

    //see if the current buffer contains the start code.
    if(buffer[0]==0x00 && buffer[1]==0x00 && buffer[2]==0x01 && buffer[3]==0xb6)
    {
        //vop start code found
        //Test for I-frame
        unsigned char ch = ifs.get();
        int vop_coding_type = (ch & 0xc0) >> 6;   //masks out the first 2 bits and shifts them to the least significant bits of the uchar
        if(vop_coding_type == 0)
        {
            //It is an I-frame
            //...
        }
    }
}

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Answer 2

Windows VFW I-. I-, FindSample FIND_KEY.

Answer 3

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