Comment by kuschku
2 months ago
You can get the original compressed h264/h265/etc stream back out, that's the entire point.
Even DRM media is using regular accelerated video decode.
2 months ago
You can get the original compressed h264/h265/etc stream back out, that's the entire point.
Even DRM media is using regular accelerated video decode.
The "entire point" of contemporary lossy-media DRM [0] is to prevent you from doing that. You can only do so if the DRM scheme is circumvented or unsound [1].
That is not what we're talking about - the working assumption here is that the DRM scheme is sound and effective. In which case your only possible but also guaranteed stage of recapture is at the analog hole, by which point the media encoding is already undone, incurring a generational loss.
[0] I consider presently existing and historical DRM implementations deeply flawed and misguided; they severely overstep their boundaries implied by the name "DRM", in certain cases quite disgustingly - hence the many added adjectives for clarification
[1] puzzlingly, any access control will actually get you in the same legal situation, regardless of whether the access control mechanism is effective or sound, so this is actually a design decision; but it's pretty universally taken afaik.
> That is not what we're talking about - the working assumption here is that the DRM scheme is sound and effective.
Lol. That is not possible.
If I'm able to watch something, my device must be able to decrypt the DRM. If my device can decrypt the DRM, I can take my device apart and figure out how it does this, and do it myself.
The most DRM encumbered format is DCP, used my cinemas. Each projector has a unique key burnt into it, the decryption, decoding and watermarking happen on the same piece of silicon, and the entire device is built like an HSM, opening it wipes the keys.
There are bit-perfect DCP rips on the high seas, with the original compressed data.
HDCP is meant to prevent me from copying HDMI signals. Every conference center and lecture hall has cheap Chinese devices that remove it.
Regarding the analog hole, with a properly calibrated professional video camera recording in RAW, with both camera and monitor genlocked and color calibrated, and the proper postprocessing, you can capure the original pixel values exactly.
I've done that part more often than I'd like...
And worst case, you can then brute force which parameters the original encode used to re-encode your data without generation loss.
> Lol. That is not possible.
It is possible, both under the conservative interpretation of the word (like how AACS is continuously updated as security holes are found and compromises happen, with the keys being rotated each time), and on a theoretical level (FHE). The latter is not being done because it is not nearly performant enough, and the former is an ongoing cat and mouse game that is once again irrelevant to what we were discussing here.
With FHE, the "take the machine apart and analyze what it does to get the original bitstream" would be cryptographically hard, so good luck with that. With the usual DRM schemes it isn't, so they are pretty much always cracked in a few months or a few years, but until that point they are both sound and effective.
> Regarding the analog hole, with a properly calibrated professional video camera recording in RAW, with both camera and monitor genlocked and color calibrated, and the proper postprocessing, you can capure the original pixel values exactly.
Yes, that's what I'm suggesting too...
> And worst case, you can then brute force which parameters the original encode used to re-encode your data without generation loss.
Can you? I mean in practice, in a practical amount of time. And is that actually done?
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