ARE there projectors/media servers that can't play 4K DCPs?

[Kieran Hall]

Hi all

This feels like a daft question since I was sure the answer was 'no', but one thing that came out of the rerelease-heavy response to the pandemic here in the UK was the amount of reassurance we got from distributors about having 2K DCPs available.

One "4K restoration" was "restored in 4K" but only had a 2K DCP available because of "compatibility reasons", and now Paramount are promising that their rerelease of The Godfather will have 2K DCPs available "for sites that can't play 4K".

Of course, there's an argument to be made for 2K DCPs being a better use of bitrate when played back on a 2K machine, but are there any in-use projectors or media servers that cannot play 4K content at all?

[Steve Guttag]

This is a complicated question and simple, at the same time! The simple answer is, all DCI compliant servers (DCI compliant on the day they applied...not for any changes that may have been made post-manufacture...note, there were requirements for things like SMPTE packages on those servers before distribution adopted those changes) can "play" 4K DCPs. The only frame rate that has to be supported is 24fps.

What can confuse some is that just because a server can handle 4K content does not mean it has to output 4K content. So, if you have a Dolby DSS100/DSP100, it will play 4K content but it can only output the content in 2K. The only way a projector can display 4K is:

• The projector itself is 4K in resolution.
• The mediablock (could be an IMB, IMS or even a quad-link HDSDI) has to be 4K capable and, in some cases, licensed.
• The content has to be formatted in a DCI compliant manner for the vintage of the server (frame rate and data bandwidth).

If you receive 4K/24fps content, most any DCI compliant server from any era should be able to handle it. The 2K servers will extract the 2K portion from the DCP and output it as 2K. If the content is say 25fps, or 30fps, then you could have some servers that can, and some that cannot with the older servers being more restrictive.

Additionally, all DCI compliant projectors (so all series 2 and beyond and many/most/all series 1 projectors) should be able to handle a 4K image coming its way and downscale it to its native 2K imager (presuming a 2K projector). The requirement for 2K and 4K support via DCI was on both pieces (projectors and servers). Since there were no Series 1 projectors that were 4K and there are no IMB/IMS designed to go into a S1, this is going to be a very rare to non-existent case. I don't recall if the NEC S1 projectors had a quad-link option or not. I know that their S2 projectors have four SDI inputs. Christie has a quad-link SDI PIB module (option) and Barco also had a quad-link SDI board for their S2 projectors (again, as an option).

[Marco Giustini]

I’ve also seen instances where the distributors are releasing both 2K and 4K versions of a DCP and I don’t understand why.

[Leo Enticknap]

I suspect that what Paramount actually means is "for sites that can't handle DCPs with bitrates above 200 MBPS." Over the last five years or so, the average bitrate of DCPs has been increasing; especially 4K ones. I can't remember the precise figures (I'm sure Steve can!), but if my memory is correct, the DCI spec with regards old school dual SMPTE 292 / HD-SDI media blocks is that 200 is the maximum limit that the media block and projector have to support; but IMBs can go higher. The Barco ICMP-X is claimed to be able to cope with up to 350 for HFR titles. Just for giggles, I once ripped a 4K/UHD BD of a 60 FPS HFR movie and rendered a DCP of it at 350 MBPS (took my PC nearly three days to do it!). Every Series 2 IMB or later I've tried it on played it OK, if the projector could handle it (i.e. not a Series 2 ICP, which tops out at 30 FPS for 4K). A DSS200/cat862 played it into a DP2K-15C at 2K/60 OK, but all the other HD-SDI media blocks I tried it with would not play it.

[Steve Guttag]

I believe 250Mbps is the top end of original DCI equipment. The bottleneck for most S2 systems is the ICP itself. This is one of the reasons why the ICMP was able to bust through the bandwidth barrier...it replaced the ICP as well as the server. S3 and S4 projectors are, by definition using their own ICPish boards (NEC's FMT, Barco's ICP-D or ICMP, I forget Christie's ICP equivalent). The later servers, IMS3000, SR-1000, ICMP-X, IMB-S3 are going to have much higher bandwidth capabilities for higher frame rates and 4K or even 4K 3D.

[Marco Giustini]

But this is JPEG bitrate. Once it's decoded and reached the ICP, it's a 12 bit-444 video as always. It won't matter if it's decoded from a 10Mbit/s DCP ot a 1000Mbit/s DCP.

4K 4096x2160 RGB 12Bit 4-4-4 video is 955Mbit/s uncompressed. After the video is decoded, I believe this is what goes through the ICP. The Bandwidth Leo mentions is - IMHO - only affecting the media block.

Clearly, to deal with 4K and higher framerate, you also need video processing electronics capable of dealing the extra bandwidth - a 48fps video of the above would be 1.91Gbit/s

[Leo Enticknap]

I looked it up (DCI document, version 1.3).

The storage system is required to provide enough output to support a continuous stream of 307 Mbits/sec for compressed image, uncompressed audio (16 channels, 24 bit sample, 96 kHz) and subtitle data to allow for non-interrupted Digital Cinema playback.

7.5.4.3 gives the same figure for the media block, plus 20 MBPS for subpicture, and 37 for audio.

The Media Network is a high bandwidth, switched interface, made up of media interfaces, Disc Arrays and Media Blocks. The Media Network is required to support sustained rate of 307 Mbits/sec for compressed image (250 Mbits/sec), audio (37.87 Mbits/sec - 16 channels, 24 bit sample, 96 KHz) and subtitle data (subpicture 20 MBits/sec) for each screen. Additional data bandwidth is needed for ingesting new content and control/monitoring.

A 4K distribution shall have a maximum of 1,302,083 bytes per frame (aggregate of all three color components including headers). Additionally, the 2K portion of each frame shall satisfy the 24 FPS 2K distribution requirements as stated above. Note: For information purposes only, this yields a maximum of 250 Mbits/sec total and a maximum of 200 Mbits/sec for the 2K portion of each color component.

So the crucial figure is 200 for the image on 2K only equipment, rising to 307 for DCPs that are over and above 2K at 24 FPS. I would guess, therefore, that Paramount's 2K versions have an overall bandwidth within that 200 for the pix limit (plus 37 for the audio and another 20 for everything else), whereas the 4K versions could go up to 307.

[Carsten Kurz]

One "4K restoration" was "restored in 4K" but only had a 2K DCP available because of "compatibility reasons", and now Paramount are promising that their rerelease of The Godfather will have 2K DCPs available "for sites that can't play 4K".

That is nonsense. We see many mainstream 4k DCPs these days, the number is increasing in recent years. If there were any DCI compliant systems without 4k support, all these movies would have had to be supplied in 2K versions as well. Non 24fps Frame rate can be an issue, bit rate is sometimes an issue, but 2k vs 4k, no. We sometimes get warnings from studios when they release a 25fps movie. I have never ever seen something like this about 4k DCPs.

Occasionally there were issues that were 4k related but not strictly to the J2K part - I remember that 'The Revenant' was released as a 4K Interop in europe, and had bitmap/PNG subtitles for the indian language. These were an issue for some systems, rendering the PNGs wrong size. But the movie played, and when they released a new VF with the subtitles as timed-text, it had no issues anymore. The trouble here was that 4k Interop + 4k PNG was not properly defined in the Interop papers. There were similar issues with some systems that had 4k capable and 4k enabled media blocks in 2k projectors, but did not use the proper PCF. That was just a config problem. But again, these were just minor subtitle issues, and I haven't heard about it for years. Still, some studio people may have heard that 4k would have caused issues somewhere somewhen, so want to play safe.