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I think the greater problem with 4K is delivery affected by bandwidth. We’re somewhat pushing the limits of 1080i/p across satellite and cable and even that is delivered in compressed form. Add to that the advanced sound codecs and the bandwidth per channel is considerable. Right now the only way to have an uncompressed 1080p signal is through Blu-ray disc.

There is no such thing as a delivery medium that does not use compression. The max bitrate for Blu-ray is 40 Mbps and it is highly compressed. 40 Mbps is the peak (for the video portion), but most discs are much lower than that, on average, such as 20 - 30 Mbps. An uncompressed 1080p 24 fps video takes this many bits:

1920 * 1080 * 24 bits/pixel * 24 fps = 1194 Mbps

And a 4K stream would be 4777 Mbps. We will never have such a format...and we don't need it. MPEG-2, H.264, etc compress this by converting to YUV (or YCbCr) which converts to luma + chroma and removes 75% of the chroma data, then their is some lossy compression as well as some lossless compression to get 10-20x smaller data.

When you move to 4K resolution you have 4x the number of bits in the uncompressed file, but the compressed file does not grow by 4x. You get higher compression ratios just from the physics involved (I can explain if needed). So while Blu-ray is 40 Mbps max and maybe 25 Mbps typical, a 4K video might be 30-35 Mbps typical and 60 Mbps max with the same quality per pixel. To confirm, just take your 15 or 20 MP camera and take a few shots at each different resolution and see how large the JPEGs are. Higher resolution needs fewer bits per pixel because there is less unique information per pixel (think about the anfle of view for each pixel as your eye sees it)

We aren't pushing the limits of cable or satellite. They keep adding channels to use up bandwidth. They could easily reduce channel count and increase Mbps per channel, if they wanted to and if people would pay for it. It isn't a technical problem, it is a business choice.

delivered to theaters on hard drives since there’s no real way to transmit directly to the theater.

They could easily send via Internet or satellite. The issue is security, accountability and reliability. Sending a HDD has about the same delay as sending reels of film and is cheaper. And they are (or were) working on a industry spec for electronic delivery.

Or, and this is not left field, a new loss-less video compression forced into being because of limits on bandwidth.

There are some lossless compressions schemes for things like WiGig that are being developed. They'll never be used for video delivery.

We do have HEVC (unofficially H.265) which will soon be at version 1.0 of the spec. HEVC will get about 2x better compression than H.264 (aka AVC) for the same quality, once the encoders are mature (maybe 2-3 years). 1080p Blu-ray quality for 8-10 Mbps, perhaps.

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