I recently completed what was perhaps the most time consuming and technically challenging project of my career to date. The task was to create a number of videos for a large UK retailer, which would be shown at their annual conference to commemorate their 30th anniversary. The event was to take place at a major London cinema and would be comprised mainly of video content, with the managing director speaking briefly between each video to introduce the next section.
It was decided that since the content would be shown on one of the largest cinema screens in Europe, we should shoot everything in 4K resolution. This presented a few challenges in itself, not least of all the total amount of editing storage I’d need for the project. In all, it came to over 4.5TB!
Whilst I could tell you all about the time consuming editing process, which in itself took over 350 hours, I’m going to focus here on the technicalities of actually getting the video and audio out of the editing software and into a format which the cinema system could play back.
The 5.1 Mix
I edited all of the videos in Adobe Premiere Pro, maintaining the 4K resolution throughout the process. When each video was ready for mixing, I exported it in Avid DNxHD format at 720p resolution, retaining its 23.976fps frame rate. Pro Tools can’t yet handle video in 4K resolution and even if it could, 720p is fine for most audio post production work anyway and it avoids having to use massive video files during the mix. The Avid video engine is optimised for use with DNxHD so video problems are minimised when using video of that format within a Pro Tools session.
I originally intended to mix everything in 7.1 but it was eventually decided that 5.1 would be more practical for this project, partly because the videos would subsequently be shown a couple of times in smaller venues where they only had a 5.1 sound system anyway. Earlier in the process of filming, I had done some test exports and surround mixes which I was able to take to the cinema and try out. After a little experimentation, I decided that mixing to the EBU R-128 loudness spec of -23LUFS would actually work really well for playback in the cinema. I did all of the mixes in Pro Tools 12 using an Avid S6 control surface.
Pro Tools Channel Order Vs SMPTE Channel Order
One consideration when mixing in Pro Tools for cinema is that Pro Tools always uses the Film channel layout (L, C, R, Ls, Rs, LFE). Whilst you can re-configure the channel mappings for output from your audio interface, anything you actually mix down will be in the standard Film channel order. Cinemas run all of their content from media servers and these systems expect the audio to be in the SMPTE channel configuration which is L, R, C, LFE, Ls, Rs. This was a challenge which I’d have to fix later in the process. More on that shortly. I used the Waves WLM Plus loudness metering plug-in for all of my mixes and once everything was done and the loudness was on target, I bounced each soundtrack down to an interleaved 5.1 WAV.
Importing The 5.1 Mixes Back Into Adobe Premiere Pro
In order to combine the completed mixes with the full quality video, I imported them all back into Premiere and synced them with the video. Premiere Pro allows for 5.1 audio tracks so this was a straight forward process. Once everything was in place and I’d watched it through a few times, I exported the video with its soundtrack, in Avid DNxHD format at its native resolution of 4096 x 2160. I used DNxHD because it is perceptually lossless and retains the colour information in the video.
Creating DCP Files
Everything you watch in a modern digital cinema is played back from a format called Digital Cinema Package, or DCP for short. Whilst it is possible to take a laptop along and plug the HDMI output into the projector, this is not a great way of doing it and you won’t be able to run the videos at full resolution plus you might be restricted to stereo sound, depending on how that particular system is set up. For this reason, I chose to encode the video files to DCP format so they could be loaded onto the cinema server system. There are various pieces of software available to create DCP files, including a plug-in for Adobe Media Encoder called Wraptor. On the recommendation of the cinema manager though, I chose to use some free software called DCP-o-matic. I was apprehensive about using free software for something as critical as this but after doing some test encodes and playing them back in the cinema, I actually found that the results were great and played back perfectly.
One of the key features of this software, from my point of view, was the ability to re-map audio channels. This allowed me to re-allocate the audio channel mappings so that the resulting file would reflect the SMPTE 5.1 channel layout rather than the Film layout which Pro Tools uses. DCP-o-matic is straight forward to use and I was able to drag and drop the master video file into it, configure a few settings on both the video and audio side and click encode.
Getting The Files Onto The Cinema Server
Perhaps the simplest part of this whole production was loading everything onto the cinema server. I dropped all of the DCP files onto a USB drive formatted as ExFAT, plugged it into the server system and dragged the files off. I’m pleased to say that they worked perfectly, which was a relief because we only finished loading the files 30 minutes before the event! Fortunately, the conference itself went extremely well and everything looked and sounded great. I was glad to rest for a few days afterwards though!