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Beginners guide to Digital Cinema Packages (DCP)

posted 17 Nov 2014, 04:54 by Ben Edwards   [ updated 14 May 2015, 15:59 ]
DCPs are how Digital Cinema Servers play films. a DCP is the digital equivalent of a 35mm film print. They are actually a directory/folder with a number of files in them. They are generally loaded onto the server (a process called ingesting) by plugging in a Hard Drive (USB2 or a faster CRU drive). 

I offer a very affordable Digital Cinema Package (DCP) Mastering/Creation service as it is very time consuming and prone to errors (DCP problems are the main reasons film festivals have problems playing films).  If you want to create your own DCP-o-Matic is a great free piece of software but allow yourself a lot of time (several days) and find a cinema you can test your DCP in.

The DCP actually contained a JPEG 2000 for each frame and a uncompressed WAV file for each audio channel.  JPEG 2000 holds a better quality image than standard JPEG but is very processor intensive to create.  Even on a fairly powerful computer (Quad core 3Ghz) it can take over 15 hours to create the 70 minute DCP.  DCPs contain a lot of data and gives a extremely high quality image.  A typical feature length film is over 150 gigabytes.  There is a quality setting in a lot of the software.  a 'bandwidth' of 50 gives quality similar to blu-ray and a 175 is roughly what feature films use.  It is no quicker to produce a DCP of a lower quality but the files are smaller (the bandwidth is Mbps so a 175 bandwidth gives a DCP more that 3 times larger).  50 does have the advantage that a feature length film can be distributed on a large memory stick.

INPUT FORMATS

To create a DCP you start with a video file (either with the audio tracks included or separate audio files or files).  Below the various video and audio formats are discussed.

VIDEO
DCP creation software can generally accept a variety of formats.  The format you should use depends on the source material the film was shot on.  For very high quality source (shot on Red or Arri Alexa) it is worth starting with 10 bit uncompressed 'YUV' video.  For other top end cameras (including Canon C300) prores 422 HQ or Avid DNxHD 180 are appropriate.  It is possible (but not ideal) to use H.264 (.mp4) but you should use a very high bitrate.  

AUDIO
Again DCP software can generally accept most popular audio formats but as they use the below format it is a good idea to start with it:

Format: Waveform Audio (WAV)
Audio codec: Uncompressed
Sample Rate: 48000 Hz
Channels: stereo (or 5.1, in which case a file for each channel can be provided)
Sample size: 24 bit

It is best to supply a audio files mixed to -12 Db or even a little lower.  If the audio level is too high you will get pooping (where the audio breaks up and crackles).  The Dolby audio decoders tend to have a 'fader' level ranging from 0-10.  If your mix is too low (even by a few Db) it will not be possible to play loud enough.  It can be tricky to get it right as -18 will probably give you a far too low level even at a fader level of 10.  If your mix does not peek between -12 and -13 some DCP authoring software can adjust the level but you need to know accurately what Db the mix peeks at.

COLOURSPACE/GAMMA
The colourspace refers to how many colours (and what colours) are used for the video.  Computer monitors normal use sRGB but broadcast monitors use Rec.709 (or even P2 for high end cinema).   Gamma refers to the brightness of the image (this is a oversimplification as it uses curves but it gives the general idea).  If set up properly a Gamma of 2.2 is generally used for computer monitors and Rec.709 also often also uses 2.2.  Digital Cinema uses Rec.709 but has a Gamma of 2.6. The DCP creation software will convert to Rec.709/2.6 but it is important to know what the source material is so the software can be set up.  If you made the video yourself on a computer monitor sRGB/2.2 is best to use.  If the video was properly graded the person doing the grading should be able to tell you.

FRAME RATE
24 is the best framerate for Digital Cinema but 25 is also an option (see Framerate section of Delivery Options Below).  The DCP software should be able to do frame rate conversion for you and this should work well. This is done a lot for broadcast TV (i.e. most films are converted from 24 to 25fps) and you will not notice.  Ideally you should shoot in the same framerate as you edit and create the DCP in but simple conversion is very rarely noticeable (and only for films with a lot of fast movement such as action films).   The best option is to export the video file in the framerate you want the DCP to be so you can view the film at the new framerate and make sure there are no issues.

Lastly if different files are delivered for video and audio they must be exactly the same length (i.e. if they are lain down in a editing system they should be the exactly the same length).  It is a lot safer to start with a single file with audio and video. If the sound mix was done in a separate program than the video was edited it is easy to accidentally to get slightly different length files (partly as video works in frames and audio in time).

DELIVERY OPTIONS

There are two types of DCP, the original interop and a newer SMPTE.  interop only suportes 24fps but only newer DCP servers support SMPTE (which can support other framerates such as 25/30).

What type of DCP you create will depend on where you are distributing it and the framerate of your edit. If it is for a specific case you should ask them what server they use and if it supports 25fps (if your source is 25)  and create a SMPTE.  24fps Interlop is the best if you are delivering to multiple unknown venues but if your source material is 25fps SMPTE 25fps is probably the best option if you can confirm the venue support it. It is possible to put two versions on the same drive so for 25fps material a 25fps SMPTE and a 24fps Interlop is a good idea.  It will mean 2 DCPs need to be created so it may cost twice as much as it takes doubled the processing time. 

ENCRYPTION(KDM KEYS)
It is possible to have encrypted DCPs but these will require a key to be sent to each venue which unlocks the DCP for a specified number of days (The process also requires the venues to send the ‘certificate’ for their server to you).   There will geenraly be a cost for creating eatch certificate (£10-£20).

A much simpler option is to not encrypt the DCP and this is probably the best option unless you are doing a full cinema release. Some independent cinema releases are distributed uncompressed as it is very difficult to turn them into a format that can be played without a full digital cinema setup (costing over £20,00).  Some film festivals will only accept uncompressed DCPs.

MEDIA
There are a number of options here:
  • USB stick - This is best for short films
  • Portable USB Drive - This is a good budget option for longer films.  Portable (2.5") drives are populer as they are smaller so cheaper to post.
  • CRU Drives - These drives allow material to be ingested into the server quickly but are more expensive.
As a side note all DCP servers can read Linux formates drives  (although some can read Windows NFS drives).  These have to be specially formatted to a specific Linux type.  USB sticks are generality windows formatted (vFAT/FAT32) as should be able to be read on all servers.

Formatting Linux drives requires running Linux and is covered half way down http://www.knuterikevensen.com/?p=437