FIELD GUIDE / DCP
The Digital Cinema Package represents today's version of the release print, defined by the Digital Cinema Initiative (DCI) and SMPTE. The Studios invented the DCP to save the costs of analog prints and shipping, but also to offer better image quality to the audience: no loss printing copies, no wear & tear during repeated presentations.
A DCP consists of two mxf files, one for picture one for sound, plus some descriptive text files. It is carried by conventional storage media, like a hard drive, SSD or flash drive, formatted with the linux file system. Studios also send DCPs over satellite or the Internet to multiplexes.
The critical part of creating a DCP is the encoding of the image. Digital cinema uses an uncommon image codec and unique colorspace and gamma value. The sound is wrapped untouched in it's own mxf container.
BIT DEPTH 12 bit
BITRATE ≤ 250Mbit/s
CHROMA SUBSAMPLING 4:4:4
COLOR SPACE XYZ
RESOLUTIONS 2K OR 4K
ASPECT RATIONS FLAT OR SCOPE
BIT DEPTH 24 bit
SAMPLE RATE 48KHZ OR 96kHz
CHANNELS max. 16
Depending on the workflow and available processing power, encoding time of the image can vary greatly. The DCP's image codec jpeg2000, short j2k, and RED's REDCodeRAW share a similar modern wavelet architecture and demand higher computing power for encoding and decoding than other codecs.
Similar to the proprietary decoder card for working with material from the RED cameras, j2k hardware encoders like the Clipster were the fastest option to encode DCPs for a while. Today's highly optimized software encoders like EasyDCP and FinalDCP can exceed the speeds of hardware solutions using parallel processing, GPU acceleration and distributed rendering on multiple machines. The Openjpg codec, open source DCP-creation software like OpenDCP or DCP-o-matic is based on, become more optimized as well.
The wavelet codec jpeg2000 can also be decoded at lower resolutions, like REDCodeRAW. A 4K DCP can be played back in a 2K theatre and vice versa, but with cost in image quality.
Since most theaters, especially art house cinemas, are equied with smaller 2k screens, where an upgrade to 4k would be of no benefit to the audience. Since the maximum bit-rate is 250Mbit/s, a 2k extract of a 4k DCP would only use 1/4 of the data rate (63 Mbit/s). Therefore 2k-DCPs will offer highest image quality in most cases for independent cinema projects.
DCP servers in the cinema have an USB port and an internal SATA interface. Post-production houses and Projectionists naturally prefer to work with a drive for the SATA carrier, usually the DX115 DC by CRU, which allows for a faster creation and transfer in the cinema. The deluxe DCP would be replacing the HDD with a more reliable and lighter SSD. SSD also have the advantage of even higher read/write speeds.
For several years a studio release would have been distributed on a 3,5" HDD in a DX115DC carrier in a bulky pelican case. Today's delivery of the heavy hard plastic cases are replaced by slim cardboard boxes to save shipping costs.
For independent films, 2.5" USB HDDs are the standard and the logical economical solution.
INTEROP AND SMPTE DCPs
The newer SMPTE-standard is now widely accepted and offers better compatibility between DCP-hardware vendors. The drawback of interop was it's limitation to 24fps. Documentary films in Europe for example are often shot in 25 fps. The necessary frame rate conversion to 24 fps was a considerable invasive procedure, especially for the sound. A 4% slower playback rate, changes the pace and lowers the sound by about a half tone, and if pitch corrected, artifacts are introduces. Today the SMPTE standard allows 25fps and preserves the original speed of those pictures.
3 options exist: Soft subtitles either rendered in realtime by the DCP server using the CineCanvas system or pre-rendered as PNG images or hard coded subtitles burned into the image during encoding of the DCP. Festivals typically strongly recommend burned-in subtitles.
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