How can I tell if a video has been digitally watermarked?
Are there watermarking methods that don't change the file's hash?
Is this technology even used frequently?
>>54656325
>How can I tell if a video has been digitally watermarked?
Did you try looking for a watermark?
>How can I tell if a video has been digitally watermarked?
Compare it N different copies. Assume some distribution and select some p-value and test the hypothesis.
Just Bing it keywords: Statistics
>Are there watermarking methods that don't change the file's hash?
Usually hash functions have significantly larger domains than codomains. In these cases, definitely yes, there are ways to mutate content but maintain hash.
Just Bing it keywords: Pigeonhole principle, preimage resistance
>Is this technology even used frequently?
Why do you care? If you are trying to screencap youtube/hulu vids and post to them to PirateBay to enter teh movie skene, just forget about it.
>>54656512
>Why do you care? If you are trying to screencap youtube/hulu vids and post to them to PirateBay to enter teh movie skene, just forget about it.
I do have some videos I want to upload but I also don't want to go to jail. I suppose there really is no way to be certain.
>>54656325
>>54656617
If you have a cryptographic hash of an vanilla file and your copy has the same hash, it's in practice guaranteed to be the same file. (Note "in practice"). Current cryptographic hashes are very good.
This advice applies only to crypto hashes and certainly not to error correction/detection codes such as CRC family functions.
>>54656512
>there are ways to mutate content but maintain hash
Fascinating, if true.
>>54656325
You want to share paid amateur porn? Sneaky :^) As >>54656437 said, look for a watermark, lol. It's the only way. Otherwise just reencode it if you think it's been written something in the container.
>>54656762
Hash is a lossy compression function. Clearly more than one input will have to map to a certain output.
With proper hash functions this is hard as they are designed to protect against preimage attacks, but with a liberal definition of "hash functions" including algos such as CRC which is (was?) used in teh skene (only god knows why) this is trivial.
For example, preimage attacks on MD5 are looking to become almost practical soonish.
Theres no way you can ever know unless you manually inspect every frame of the movie.
Nothing stop them from generating the videos they serve you on the fly, injecting a 8 pt text in the corner of 1 random frame - 1% opacity, with a unique identifier string tied to your IP/account
>>54656953ffmpeg.exe -i video.mp4 -y -sameq %03d.jpg
>>54656953
So how do yify and publichd do it?
>>54656986
with clean sources
>>54656953
>Nothing stop them from generating the videos they serve you on the fly
Except the cost. It's unlikely that they rencode anything as that would prevent caching and make their servers from a nice cheap static server to some fucking (literally) encode farm.
Op, just check the URL. If it looks like a CDN, you are probably safe.
>>54656953
There are audio watermarks too.
https://en.wikipedia.org/wiki/Audio_watermark
If you're ripping something from a paid source like itunes or whatever make a new account and use a prepaid card to buy it and you'll most likely be fine.
>>54656986
>yify
You could have a fullscreen watermark with names and addresses with 200pt font and nobody could read it after their encode.
>>54656890
>You want to share paid amateur porn? Sneaky :^)
...maybe
It seems that the only way to truly be sure is to compare the hash against another version of the same file, though. Or, to transcode it, but I'm sure if they are watermarking the videos they are also using watermarks that can survive transcoding.
