Encoding and Delivering Content for Digital Cinema
By Helmut Lottenburger, DI Workflow & Application Specialist
Thanks to recent stereoscopic 3D movie releases Digital Cinema in Australia has finally gained some momentum. The demand for digital content such as show events, advertisements and movies has skyrocketed in the last six months.
Unfortunately, encoding and delivering content to a digital cinema server is not as easy as delivering a DVD. The world of Digital Cinema is dominated by acronyms. Even when deciphered most of them can still cause confusion. The widely used buzz word Digital Cinema Package or DCP, for example, is not a “package” at all. It has no resemblance to a zip file, it is not a tape, not a formatted hard drive and it’s certainly not just one single file.
Even a simple Digital Cinema Package can look intimidating to a novice eye.
Very often you may find additional subtitle XMLs included as well.
In addition to essential data like video and audio, a so-called “Digital Cinema Initiative compliant” DCP also contains metadata. Some of it is used for security reasons and some of it to ingest and allow playback on the server.
Having said that, not every package generated by a DCI compliant application will be played by every server. It is a bit like russian roulette and there is a good chance that your DCP will be rejected by a playback system. Encoding applications with high reliability may be costly, but they will ensure that your delivery doesn’t end in a disaster.
So what to do when asked to encode your final edit or production into a DCP? What are the pitfalls to look for when focusing on content creation for D-Cinema as part of your business?
Time is Money
The higher the demand for d-cinema encodings, the higher the competition. To offer competitive prices you need a highly efficient encoding pipeline. Ideally you want to import your source files into an application and kick-off the encoding. When done, copy the content onto your hard drive and send it to the client.
Unfortunately it isn't that easy in the D-Cinema world. All content you receive must be encoded into JPEG2000 files which are again wrapped into a specific MXF container. The JPEG2000 codec is very demanding and on a stand-alone high-end workstation this is often an overnight process for movies.
Before delivering your content you will want to QC it and check for colour shifts or encoding errors. Doing this in realtime is impossible without a dedicated system to decode your DCP. Additionally, your trusted RGB display device (for example your calibrated broadcast monitor) won’t be of any use. All encoded data for digital cinema resides in a X’Y’Z’ colorspace with a gamma of 2.6. When displayed on a standard RGB monitor, it will have a greenish and washed out look.
To do a decent QC you need a realtime decoder and a colorspace converter. Both products will need to be good enough to perform these tasks accurately and reliably.Note that using such a video monitor setup does not replace a proper d-cinema system. It will, however, ensure that there are no major mistakes in your encoding, like damaged image files or visible gamma offsets.
In most cases a quality check will require you to take the DCP to a cinema server and view it on a projector. Usually this costs additionally time and money which you could have spent on something else.
A Digital Cinema Package is colour independent. It therefore needs to be converted to RGB for viewing on standard display devices.
An unconverted X’Y’Z’ image will have a greenish tint on a RGB monitor.
One key for me, several for you
If the the content needs to be encrypted a whole new level of complexity is added to the process. The basics of asymmetric encryption need to be understood and QC is further limited to authorised devices only.
The basic concept behind asymmetric encryption is to enable the playback on one system only, while at the same time allow multiple encodings from a variety of sources. This means that one unique private key is held by the cinema server and a second (public) key is given out to content distributors. In short: Many can encrypt but only one can decrypt the content.
The management of several dozen or even hundreds of keys for all the cinemas out there can be a business model for itself and you have to ensure meticulous house-keeping when dealing with all these so-called Key Delivery Messages.
3D - Double the trouble
Stereoscopic 3D in Digital Cinema is achieved by interleaving left and right eye, e.g. L/R/L/R/....
Reviewing a 2D DCP is already quite tricky but to QC a stereoscopic encoding in 3D you certainly always need a d-cinema playback system. A 3D DCP is one single stream of interleaved left and right eye at 48fps. Usually this signal is transmitted over a Dual-SDI link and only very few 3D monitors on the market can display such an input without prior image processing.
Solutions and products for creating your own DCP can be found for every budget. If you are doing only a few encodings per month and have a good understanding of video technology, most of these applications should suit you. However, keep in mind that very few products on the market will offer you a flexible end-to-end workflow.
Digistor believes that the turnkey workstation DVS Fuze is the only product to offer an efficient and flexible workflow for focusing on D-Cinema encoding as part of your business. Using DVS Fuze, almost any incoming data can be scaled, encoded and encrypted in a single realtime process. Once this is done, you simply load it back into the same machine and QC it. The whole process of decoding and decrypting is done automatically. Colorspace transformations to RGB are fool-proof and all settings can be done in an Avid-style user interface. Neat!
And yes, 3D DCPs can be encoded as well. Furthermore, you can even view it on any available 3D display device or directly on your computer screen with coloured glasses. Feel free to contact us if you have any questions!
- Record & Playout of all SMPTE video formats
- Drag data into the timeline, set Fuze into Slave-Mode and use it as a VTR replacement!
- Image sequences (DPX, TGA, TIFF, etc)
- Quicktime, MXF (DNxHD), MPEG-1, MPEG-2 & more.
- All formats are natively supported and available instantly for editing
Digital Cinema Encoding in Realtime!
- Import the above formats
- Apply scaling, edit the data and do color conversions
- Setup your d-cinema reels freely
- JPEG2000 encoding and MXF wrapping
- Encryption for multiple d-cinema severs
- Import any DCP, edit it in the timeline and output it again
- If you have the key delivery message you can even do this with an encrypted DCP
- Check your content on a Broadcast monitor if you don’t have a d-cinema handy. All colour conversions are done automatically.
Stereoscopic 3D features in realtime!
- Create 3D DCPs and play them back as well
- Merge Left and Right eye video data in realtime
- Import a (encrypted) DCP and split it into Left/Right eye again
- ALL stereo modes are supported (Anaglyph, Interlaced, Top/Bottom, Side-by-Side)
- DVI video output and 4x HD-SDI interfaces