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• How can I programmatically write and read random video watermarks ?

  13 novembre 2017, par GreenTriangle

  I spent a few minutes trying to think of a clearer way to word my title, but I couldn’t manage it, sorry.

  I want to essentially canary trap video files : I am (hypothetically, this is not real but a personal exercise) offering them up to 5,000 different people, and if one gets leaked, I want to know who leaked it. Metadata is too easily emoved, so what I’d like to do is add a random and subtle watermark to each file, and store information about that in a database.

  For example : on Joe Smith’s copy, a 10x10 pixel 80% transparent red square in the upper left corner for 5 frames. On Diane Brown’s copy, a full-width 5-pixel 90% transparent black bar on the bottom edge for 15 frames. Then, if I find a leaked copy, I could check it against the database.

  I know this still isn’t foolproof : cropping would break co-ordinates, hue/brightness transforms would break colour reading, cutting time would break timestamps. But if I did want to do this anyway, what would be a good strategy for it ?

  My idea was to generate PNG overlays randomly, split the video into parts with mkvtoolnix/ffmpeg, re-encode the middle part with ffmpeg + overlay filter, and then rejoin them. But is this silly when there’s a "proper" way to do it ? And what would I be doing to read the watermarks, which I can’t even really conceive of ?

• How to dump RTSP to raw data file without encoding

  28 juin 2020, par Yves

  I've read this link : How to dump raw RTSP stream to file ?

  


  In this link, it seems that dumping RTSP stream to some formatted file, such as mp4, is normal.

  


  But I want to store the RTSP stream into the raw data files, instead of files like mp4, avi etc. And I should be able to extract data from the raw data files and send it out as RTSP stream too.

  


  In a word, this is what I need :

  


  

  1. receiving RTSP stream ---> 2. store RTSP data into raw data files ---> 3. read raw data files and send data as RTSP stream

  


  


  Why do I need this ?

  


  Because as my understanding, storing RTSP strema into some formatted file, such as mp4, needs to do an action of encoding (encode RTSP to mp4). But for me, I don't need this action, I simply need to store RTSP data and re-send it as RTSP stream. So if I can store RTSP into the raw-data file, instead of mp4, I don't need to spend computer resources on the action of encoding.

  


• bash : find truncates some paths [duplicate]

  17 novembre 2023, par fweber

  I'm using MacOS 13.0.1 and try to find + loop over .mov files to convert them to MP4 using FFMPEG. Many of my path contain spaces and special characters. I found a way of putting things together thanks to this post :

  


  function convert_to_mp4_then_rm() {
    while IFS= read -r -d '' file
    do
        ffmpeg -i "$file" "${file%.mov}.mp4"
    done < <(find /Users/f.weber/Downloads -type f -name "*.mov" -print0)
}


  


  This runs but I found a (random ?) error : it looks like some of the paths are truncated when they arrive to the ffmpeg CLI.

  


  Example to reproduce with a basic content :

  


  ll Downloads/
total 9472
-rw-r--r--  1 f.weber  staff   2,3M 26 sep 08:56 23-09-26 08-56-50-2538.mov
-rw-r--r--  1 f.weber  staff   2,3M 26 sep 08:56 23-09-26 08-56-50-2539.mov


  


  When I call convert_to_mp4_then_rm in a terminal, the first MOV file is properly processed then I have the following error from FFMPEG : /Downloads/23-09-26 08-56-50-2539.mov: No such file or directory. In some conditions (e.g. when the path is longer) the truncation is more obvious and can occur in the middle of a word.

  


  What is the explanation for this ? How to forward untruncated paths to my function's core ?

  


  Thanks !