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How encryption for Cinema Movies works

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230 points perryflynn | 1 comments | 20 Apr 25 17:52 UTC | HN request time: 0s | source
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Animats ◴[21 Apr 25 02:30 UTC] No.43748045[source]▶
JPEG 2000 for each frame? I wonder what they use for decompression. JPEG 2000 decompressors are really slow. Most couldn't keep up with frame rate without GPU support.
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userbinator ◴[21 Apr 25 04:23 UTC] No.43748484[source]▶
Dedicated hardware, not even regular GPUs. JPEG2000 decompression has a rather complex entropy decoding part which is not easily parallisable.
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fulafel ◴[21 Apr 25 08:25 UTC] No.43749538[source]▶
Only on the intraframe level - Frames are independent so overall it's "embarrassingly parallel".
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crazygringo ◴[21 Apr 25 16:13 UTC] No.43753601{3}[source]▶
There's no point to decoding in parallel if you're watching in sequence.
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dsr_ ◴[21 Apr 25 16:48 UTC] No.43753942{4}[source]▶
If your hardware can only manage 4 frames per second but you need 48, then decoding with 12 sets of hardware in parallel achieves your goal.
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Animats ◴[22 Apr 25 00:53 UTC] No.43758099{5}[source]▶
Although you still have four frames of latency if you do it that way. All the audio has to be delayed to match. Parallelized decode of JPEG 2000 frames is quite possible, though.

The choice of JPEG 2000 is unexpected. Most of the neat features of JPEG 2000 are useless for cinema. Being able to construct a low-rez version from a truncated file isn't useful. Nor is the ability to divide the image into tiles and decompress different tiles at different resolution. (That's used in JPEG 2000 medical and military imagery, where you want to zoom in on the interesting part and see it in lossless mode.) You can have more than RGB or RGBA layers, which the multispectral imagery and prepress people like. Maybe the advantage is that you can have more than 8 bits of color depth.

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1. nehalem501 ◴[22 Apr 25 09:51 UTC] No.43760467{6}[source]▶
The ability to read a lower rez version of the images is a feature that is actively used. That way you don’t need to have both a 2K and 4K DCP for movies that have a 4K version, 2K projectors can simply decode the 4K DCP at 2K resolution.