Is the file size of my DCP too large or too small?

Comparing compressions between projects, is like comparing file size to pumpkins
Creative Commons photograph courtesy of CharlesAPhillips63

What size should a Digital Cinema Package be? While is my file so big? Is my output so tiny I should worry about the quality? The most common questions we get at Ask the DCP Master are about file size. But fear not – we can help!

How Large Can a DCP File Size Be?

Regardless of resolution, most DCP’s have a bitrate limit of 250 Mb/s. That’s more than eight times the data of a typical Blu-ray. Best practices are not to go right to that cap, but it gives us an maximum file size – no matter if it’s a 2K or a 4K DCP. At 250 Mb/s an hour of video would come out to 113 GB per hour.

All audio in DCP is 48,00khz, 24-bit, and uncompressed. That roughly works out to 500 MB per hour, per audio channel.

There’s some other elements inside a DCP (metadata, captioning assets…) but the files are so small, we can generally ignore them.

So a 90 minute DCP (any frame rate or resolution), with a 5.1 soundtrack would have a maximum file size of about 174 GB.

If your file is larger than this range – it is almost certainly not a valid DCP and playback will likely fail.

How Small Can a DCP File Size Be?

DCP’s use variable JPEG2K compression which means there’s no real “lower limit” on file size. The more you compress a film, the smaller it will be – but also the lower quality the image will be. There’s no agreement on “best practice” for minimums – even among major movie studios.

As a rough rule-of-thumb, here at The DCP Master, we pay special attention to any Digital Cinema Print that is less than 0.75 GB/minute.

What Is The “Best” Compression Setting For My Film?

Unfortunately there is no “one size fits all” answer to this. A large part of what we do is determining what level of compression is appropriate for each project. The type of material, resolution, frame rate, aspect ratio all play a part. A moody, lengthy, two-shot will compress differently from a vibrant kinetic action scene. 3D and 2D films have very different considerations as well.

This is one of the reasons we recommend filmmakers not use automated plugins. Often these tools have limited (or nonexistent) encoder controls. When filmmakers output a package that they know is wrong they often have no way to investigate or correct the problem.

Are There Any Exceptions To File Size Limits?

The limits for DCPs are the same regardless of resolution or aspect ratio (so the math is the same if it’s a 2K scope or a 4K full container project). But there is an exception for some HFR (High Frame Rate) projects at 60 fps or above. These projects need special equipment to play back correctly however.

 
Do you have questions to help size up the confusing world of Digital Cinema? Don’t worry Ask The DCP Master is here to help. Check out our most common questions, or ask your own.

Are you an independent filmmaker, distributor, or festival looking for professional, indie-friendly, DCP services? Visit TheDCPMaster.com to see what we can do for you!