Offline and online editing explained: proxies, conform and reel identity

What “offline” and “online” actually mean

Offline editing is the creative pass: the decisions about which take, in what order, cut where. Online editing is the finish: conform, colour, titles, visual effects and the final render for delivery. The distinction is not about quality of work — it is about which copy of the footage the work is done on. Offline runs on lightweight stand-in media; online runs on the full-quality camera originals.

The words are inherited from videotape. In the 1980s an editor cut on cheap dubs in an “offline” suite, then walked the decision list into an expensive “online” bay where the master tapes were assembled frame-accurately for broadcast. The machinery is gone; the division of labour survived, because it was never really about tape. It was about doing the slow, exploratory, change-your-mind work on media that is fast to handle, and reserving the full-resolution media for the one pass where it matters.

Why the split survives in a RAW world

It would be reasonable to assume modern hardware killed the offline/online split. It did the opposite. Camera data outran the machines that edit it. A single hour of 8K BRAW or R3D is hundreds of gigabytes; a laptop will not scrub it, and a shared project cannot pass it around. So the edit happens on proxies — ProRes Proxy mirrors at roughly 20 GB per camera-hour instead of hundreds — and the camera originals sit untouched until finish. That is an offline/online workflow, whether or not anyone calls it one. The mechanics of generating and attaching those proxies are covered in the RAW proxy workflow guide.

Two forces keep the split in place. The first is weight: you cannot carry RAW to a coffee shop, but you can carry proxies anywhere. The second is division of labour: the editor cuts, and a colourist or finishing artist conforms and grades, often on a different machine in a different room. Both forces point to the same architecture — edit on light media, finish on heavy media, and build a reliable bridge between them.

The bridge is identity, not file paths

Here is the idea that everything else depends on: the connection between a proxy and its camera original is not the folder it lives in. Move the media, rename the folders, copy the drive to a new machine, and a path-based link snaps. What survives is identity — three pieces of metadata that travel inside the files themselves:

• Filename (the clip’s own name, e.g. A001C012_240815_R2XY), which must be identical on the proxy and the original.
• Start timecode — the frame the clip begins on, so an NLE can line proxy and original up frame-for-frame.
• Reel / tape name — the roll the clip came from, the field that disambiguates two cameras that both start a card at A001C001.

That is the identity triple. A conform relinks by matching it, not by matching folder positions, which is why the single most destructive habit in post is renaming original files after the offline is under way. Rename the proxy’s display name in a bin all you like; touch the source filename and you have quietly cut the wire the finish runs on.

What a conform actually does

A conform is the act of rebuilding the locked edit against the online media. Nothing about the creative decisions changes: the same clips, the same in and out points, the same order, the same duration. What changes is the media each edit event points at — from the proxy that carried the cut to the full-resolution original that carries the finish. The finishing application reads a description of the edit, finds each source clip by identity, and lays the timeline back down frame-accurately at full quality.

The description of the edit is an interchange file. It is the offline’s only export that matters for finishing, and it carries a list of edit events: for each one, the source clip, its source in/out timecode, and its position on the record timeline. It does not carry the media — that is the whole point. It carries the decisions, and the media is found again on the other side by identity.

The three interchange routes

There are three formats a conform usually travels on, and they carry different amounts of the edit. Choosing the right one is a downstream decision: send what the finishing seat reads best.

EDL (CMX3600). The oldest and most universal. A plain-text list of edit events keyed on source timecode and reel name, one event per line. It carries almost nothing but the cut — no effects, essentially one video track, an eight-character reel limit inherited from tape — and that spartan quality is exactly why it is bulletproof for a pure picture conform or a round-trip to a grading application. When the job is “rebuild these shots at full res and grade them,” an EDL rarely lies.

XML (FCPXML and the older Premiere/FCP7 xmeml). The middle route: it carries multiple tracks, references clips by file and timecode, and preserves at least some effects, speed changes and titles. It is also the format most exposed to dialect problems — a file written by one application and read by another can lose the parts the reader does not understand. Which format carries which parts, and why there is no direct XML path between Final Cut and Premiere, is the subject of the FCPXML vs Premiere XML guide.

AAF. Avid’s interchange and the standard hand-off into audio post. It carries multitrack audio with edits and some processing intact, and it can embed or link media, which is why the mix almost always crosses to a digital audio workstation as an AAF rather than an EDL or XML.

Alongside these sits the humble ALE — not a conform format in itself, but the metadata log that carries tape and source-file identity into the finishing system, so the relink has the reel names it needs to match against. When conforms fail on identity, an ALE is often what repairs them.

The handoff: what to lock before online

A clean conform is set up at the offline end, not rescued at the online end. Before the interchange leaves the edit:

• Lock picture. Online assumes the cut is final. Every change after conform is re-conform work, and re-conform is where notes and versions start to drift.
• Export a reference movie alongside the interchange — a single flattened render of the locked cut, with burn-ins for timecode, clip name and version. It is the finishing artist’s ground truth: if the conform matches the reference frame-for-frame, it is right. A 30-minute cut at H.264 10 Mbit/s is roughly 225 MB, so the reference travels easily.
• Confirm the originals are available and unchanged — same filenames, reels intact, nothing re-wrapped or renamed since the proxies were made.
• Confirm a single project frame rate. A conform that spans 25 and 23.976 fps material is a conform waiting to slip, for reasons the frame-rate mismatch guide lays out in full.
• Include handles. A few frames either side of every cut give the finish room to adjust an edit or add a dissolve without going back to the offline.

Done right, the online session opens the interchange, relinks against the originals, matches the reference and moves straight to grade. Everything above is what turns that from a hope into a routine.

How conforms die

• Originals were renamed. The identity triple broke, and the relink matches nothing — or worse, matches the wrong clip. Rename in bins and proxy display names, never on source media.
• Reels collide or go missing. Two cameras both named A001, or an EDL truncating an over-long reel to eight characters, and the conform links the right timecode to the wrong roll.
• Frame rate was mixed or misread. A single misjudged rate flag turns every timecode into a lie; if the offline was cut across rates, the finish inherits the drift. See the timecode drift guide for how a wrong rate re-interprets an entire reel.
• Effects did not cross the dialect. Speed ramps, warps and third-party effects that an XML round-trip cannot describe come back flattened or gone; plan to re-create them in the finish rather than trust them through the interchange.
• Retimes rounded. A 43.7% speed change stored as an integer somewhere lands a frame off; check every retimed shot against the reference, not against faith.
• Audio arrived at 48.048 kHz. Pull-up and pull-down sample rates ride through a conform silently and surface as sync that wanders across a reel.

Every one of these is an identity or metadata failure, decided long before the online seat. A conform is only as trustworthy as the offload and organisation that fed it — which is why the offline/online split is really a discipline about carrying identity intact from the card onward, a chain the dailies workflow guide follows end to end.

Where Launchr Post fits

The offline/online split only works if the identity triple survives every hop between the card and the finish — and that is precisely the thing manual workflows lose. Launchr Post keeps it intact on your Mac: it offloads with checksum verification, generates proxies that carry the same filename, start timecode and reel as the originals, and exports the editor package with the interchange files and a burned-in reference movie the finish can conform against. When the cut is locked, the originals are exactly where the relink expects them, named exactly what the relink is looking for. And when the finished master comes back, the same chain carries on to client review and approval — the last link between a conform and a sign-off.