DCP-o-matic-combiner is a free, open-source Mac utility that packages your finished film or video project into a DCP — the encrypted, standardised format that professional cinema projectors actually play.
What is DCP-o-matic-combiner?
DCP-o-matic-combiner is the companion tool to DCP-o-matic that merges multiple separately-encoded DCP reels into a single, ready-to-deliver Digital Cinema Package. Where the main DCP-o-matic application handles the transcoding of raw video, audio tracks, and subtitle streams into JPEG2000/PCM reels, the combiner's job is the final assembly step — stitching those reels together with a corrected playlist and package metadata so the result plays as one seamless feature on a theatrical server.
If you have ever tried to hand a cinema a hard drive only to be told your package is malformed, DCP-o-matic-combiner is what stands between you and that embarrassing conversation.
What does DCP-o-matic-combiner do best?
It excels at taking the pain out of multi-reel assembly — a task that is otherwise a hand-crafted XML nightmare. Independent filmmakers, film-festival programmers, and post-production houses on tight budgets reach for this tool when they need to combine an intermission-split feature, a multi-language DCP with separate audio reels, or a programme of short films into one deliverable package without paying for a full DCI-compliant mastering suite.
- Reel merging — combine two or more encoded DCP reels into a single composition playlist
- Metadata correction — rewrites the asset map, volume index, and CPL so the package validates cleanly
- Subtitle integration — handles separate subtitle MXF tracks alongside picture and sound
- KDM awareness — preserves encryption metadata so existing KDMs remain valid on the merged package
- Lightweight footprint — no subscription, no dongle, no background services phoning home
Is DCP-o-matic-combiner free?
Yes — DCP-o-matic-combiner is completely free to download and use for any purpose, including commercial film deliveries. The entire DCP-o-matic suite is open-source software maintained by Carl Hetherington, released under the GPL. There is no "pro" tier, no watermark on outputs, and no feature locked behind a paywall. Donations to the project are welcomed on the official site, and I would encourage anyone who ships a feature film with it to throw a few pounds the developer's way.
Who should use DCP-o-matic-combiner?
The primary audience is independent and micro-budget filmmakers who are mastering their own DCPs rather than paying a post house to do it. If your workflow already uses DCP-o-matic for encoding, the combiner slots in naturally as the last step before you write to an NTFS-formatted drive and hand it over to the projectionist. It is also useful for festival technical managers who need to re-package screening programmes on the fly, and for film-school students who need to understand the DCP format without access to commercial tools like Clipster or easyDCP.
It is decidedly not a beginner tool in the broader sense — you need to understand what a CPL, PKL, and MXF are before you can use it confidently — but within that audience it removes an enormous amount of tedious, error-prone manual XML editing.
How does DCP-o-matic-combiner compare to alternatives?
The honest answer is that there are very few direct free alternatives. easyDCP is the industry-standard GUI tool but costs several hundred euros per year. OpenDCP is another open-source option but development has slowed considerably and it lacks the active maintenance that DCP-o-matic enjoys. Commercial mastering suites like Clipster or SGO Mistika are in an entirely different price bracket aimed at broadcast post-production pipelines.
For the specific task of combining pre-encoded reels, DCP-o-matic-combiner has no meaningful free competitor on macOS. The main trade-off versus a paid tool is validation depth — a commercial suite will catch every DCI compliance issue before the file leaves your machine, whereas with the combiner you are relying on your own knowledge and, ideally, a separate DCP validation pass with a tool like ClairMeta or dcp_inspect before delivery.
What are the limitations worth knowing?
DCP-o-matic-combiner is a focused utility, not a full mastering suite. It does not perform colour grading, frame-rate conversion, or loudness normalisation — those happen upstream in DCP-o-matic or your NLE. The GUI is functional rather than polished; this is clearly software written by an engineer for engineers, and it shows. Occasional rough edges in the interface are worth tolerating for what you get in return: a genuinely capable, professionally-oriented free tool that film festivals around the world actually rely on.
