Joiner for DJI documentation

Install Joiner for DJI

Joiner for DJI runs on macOS 14 Sonoma or later, on Apple silicon and Intel Macs. After buying, download the app zip from your Polar receipt, unzip it, and drag Joiner for DJI to your Applications folder.

The app is signed and notarized by Apple. Confirm Open at the normal first-launch prompt.

The app works without a license key. The key in your receipt turns on automatic updates: enter it in Joiner for DJI → License…. Once a day, the app checks for a new version, shows what’s new, and installs it with Install and Relaunch. Joiner for DJI → Check for Updates… checks right away. A key works on 3 Macs. To move it to another Mac, choose License… → Deactivate This Mac first. Your receipt always has the latest version, too.

Scan the card

Take the card out of the drone and put it in your Mac’s card reader. The start screen says “Drop your drone’s card or a folder here”, and gets a button with the card’s name, like Scan NO NAME. Click it and the app looks for videos on the card.

For flights you already copied to your Mac:

Drop a card, a folder or video files on the window.
Click Choose Folder… and pick a card, a folder or the video files themselves. File → Open Folder… (⌘O) does the same.
Click Downloads, Desktop or Movies.
Click Add Folder… to keep a folder you often copy your footage to on the start screen. Right-click it to remove it.

The app also remembers the last 5 folders you scanned. They show under Recent on the start screen, and in File → Open Recent. Right-click a recent folder for Keep on This Screen, Remove from Recent and Clear Recent Folders.

The first time, macOS asks whether Joiner for DJI can read files on the card. Click Allow. macOS asks the same for Desktop, Documents and Downloads. The app never reads any of them until you click.

How a drone splits a flight

A DJI drone starts a new file every time the video reaches about 4 GB. Each file is named after the moment it started and a counter, and each has its own .SRT flight data file and .LRF low-quality copy:

File	What it is
`DJI_20260712101530_0007_D.MP4`	Part 1, started at 10:15:30
`DJI_20260712102508_0008_D.MP4`	Part 2
`DJI_20260712103446_0009_D.MP4`	Part 3
`DJI_20260712101530_0007_D.SRT`	The flight data of part 1
`DJI_20260712101530_0007_D.LRF`	The low-quality copy of part 1, for the DJI phone app

Older drones name their files DJI_0001.MP4, DJI_0002.MP4, with DJI_0001.LRF next to them. The app reads both styles.

Nothing in these names says which files belong to one flight, so the app works it out. Files are offered as one flight when they’re in the same folder, have consecutive numbers and the same video settings, and each one starts where the one before it ends.

The list

After a scan, the window lists what it found, in two parts.

At the top are the flights your drone split, under a header like “3 recordings were split into several files”. Each flight is one row with a thumbnail, the name of the file it will become (DJI_20260712101530_0007_D joined.MP4), and a line like “DJI · 3 files, 9.11 GB, 22 min · with .SRT subtitles”. Click Show the 3 files to see its parts, each with its size and length.

Since the app’s grouping is a guess, every flight starts unticked, with the reason under it: “These 3 files look like one recording: each one starts where the one before it ends. Tick the box if they belong together.” Tick the ones you agree with. The app never joins a guess on its own.

Below are the other videos, the ones in one piece, like short clips. Each row has a checkbox, a thumbnail, the file name, and a line with the date, the length and the size. They start unticked. Select All and Select None are in the header.

What else the scan found, like a file that can’t be read, is in an Also found line under the list. Click it for the details.

Videos from another camera in the same folder are listed too, and can be joined the same way.

Preview a video

Click a row and its video plays in a small panel over the bottom right corner of the list. The checkbox and the grip don’t select a row, so ticking and dragging work as before.

A video in the list plays that file.
A flight plays its first part, and the panel’s title says so, like “DJI_20260712101530_0007_D.MP4 · part 1 of 3”.
A row that says Joined and checked plays the joined file.

The video starts on its own with the sound off. The speaker button in the panel’s title turns the sound on. The up and down arrows move to the next row, and Space plays and pauses. Close the panel with its close button or with Escape.

When a video can’t be played, the panel says “This video can’t be previewed.” and the video can still be joined.

Join

The Join button says what it will do:

Join 1 Recording or Join 2 Recordings when only flights are ticked
Join 3 Videos into One when only other videos are ticked
Join 2 Recordings and 3 Videos when both are

Each ticked flight becomes its own file. Ticked videos become one more file, in the list’s order, with a row at the top of the videos for it.

The bar under the list says where the files go: Save joined files to Movies. That’s your Movies folder unless you click Change…. Under it, the app adds up the space the joins need, like “Needs 9.11 GB. Macintosh HD has 182.4 GB free.” When the disk doesn’t have enough, the line turns red and starts with “Not enough space”, and the Join button stays off until you untick something or choose another disk.

When you save to a folder on the card itself, the bar warns you: “This folder is on the card itself. The joined files will take up space there.”

While it joins, the bar shows “Joining 1 of 2” with the file’s name, and each row shows its stage: Reading, Copying, then Checking. Cancel stops it and leaves nothing half-done behind.

The .SRT flight data

A drone’s .SRT file holds its flight data for every moment of the video, and its times start from zero in each part.

When every part of a flight has its .SRT, the app merges them into one file next to the joined video, with the same name: DJI_20260712101530_0007_D joined.SRT. The lines of each part are moved by the length of the parts before it, so the joined .SRT lines up with the joined video. The text of every line is kept as the drone wrote it. The merged file is checked too, and the row says “The .SRT subtitles were joined and checked too, into DJI_20260712101530_0007_D joined.SRT.”

When a part has no .SRT, the video is still joined, and the row says why the subtitles weren’t: “DJI_0002.MP4 has no .SRT file next to it, so the subtitles can’t be joined, but the video can.”

Names

A flight keeps the drone’s name with ” joined”, like DJI_20260712101530_0007_D joined.MP4.

Videos you tick are named after the day they were recorded, like 2026-10-08.MP4. When they were recorded over several days, the name has the first day and the last: 2026-10-08 to 2026-10-15.MP4.

Joiner for DJI never replaces a file. When the name is taken, the row says “Name already used” and explains it: “A file named DJI_20260712131010_0015_D joined.MP4 is already in Movies. It won’t be replaced.” Click Save as DJI_20260712131010_0015_D joined 2.MP4 to use the next free name.

To call a joined file something else, click Rename… on its row after the join. Type the new name and press Return, or Escape to leave it as it was. The extension stays the same, and the joined .SRT gets the new name too.

The order of the other videos

The other videos are listed by the date they were recorded, oldest first, and they’re joined top to bottom. To change the order, drag a row by the grip at its right edge, or right-click it and choose Move Up, Move Down, Move to Top or Move to Bottom. Sort by Date puts the date order back.

The parts of a flight can’t be moved. Their order comes from the drone.

After the join

When a join works, its row says Joined and checked, with Show in Finder, Rename… and Move Originals to Trash… next to it. The bar sums up the run, like “4 files were joined and checked, in Movies.” and “Your original files weren’t changed.”

The app writes the joined video under a hidden temporary name. Then it reads it back from the disk and compares it with the parts, piece by piece: the picture, the sound and the drone’s own data. Then it asks macOS to open the video, and its length has to be the length of the parts added together.

Only then does the file get its name. If anything is off, the temporary file is removed and the row says Not joined with the reason. Your parts are where they were.

Free the card

After a join that says Joined and checked, you can remove the originals. Click Move Originals to Trash… on the row for that join, or in the bar for every join of the run.

The originals are the parts, plus their .SRT files when the app merged them into one. When the .SRT files weren’t merged, they stay.

Nothing moves until you confirm. The confirmation says what’s about to happen, like “Move the 17 original files to the Trash?”, and Keep Originals is the default button, so Return, Escape and Space never remove anything.

On a memory card, the Trash is on the card. macOS keeps a card’s trashed files in a hidden folder on the card itself, so they keep taking up space until you empty the Trash. The confirmation says so: “In the Trash, they stay on NO NAME and keep taking up space there until you empty the Trash.”

When every original is on a card or a drive that can be taken out, the confirmation adds Delete Now. It frees the space right away, and it can’t be undone. On your Mac’s own disk there’s no Delete Now, only the Trash.

Right before it removes anything, the app looks at the joined file once more. It has to be where it was saved, with the same size and date. If you moved it or edited it in the meantime, the originals stay and the row tells you why. A rename with Rename… is fine, since the app follows the new name.

The small preview files

Next to each video, a DJI drone saves an .LRF low-quality copy. When the videos go, the confirmation has a box, ticked for you: “Also remove the 10 small preview files the camera made (546.6 MB)”.

Ticked, the .LRF files go the same way as their videos: to the Trash with Move to Trash, deleted with Delete Now.
Unticked, they stay where they are.
Only the .LRF files of the videos being removed go, matched by name in the same folder. Another video’s .LRF, and files with the same name in another folder, stay.
When the videos have no .LRF files left, there’s no box.

A small file that can’t be removed stays where it is, and the row lists it with macOS’s reason, like “DJI_20260712102508_0008_D.LRF was left where it is.”

After it’s done, the row says Originals in the Trash or Originals deleted, and the line under the summary says what went, like “17 original files are in the Trash on NO NAME. They take up space there until you empty the Trash. The 10 small preview files the camera made went with them.” Files in the Trash can still go back with the Finder’s Put Back.

What it reads

Joiner for DJI reads MP4, MOV and AVI videos.

The videos you join have to be recorded with the same settings, like the same picture size. Making different ones fit would mean rebuilding every frame, so the app never offers them as one flight, and refuses ticked videos that don’t match, naming the odd one out.

It doesn’t trim or convert videos. It never changes, renames or removes an original, unless you confirm moving it to the Trash or Delete Now.

Troubleshooting

Parts that should be one flight show up apart

The app only puts files together when each one starts where the one before it ends. A file that can’t be read breaks the chain, and it’s listed under Also found. The parts on either side of it show as separate flights, or as single videos. You can still tick single videos and join them into one, in the order you want.

The folder couldn’t be read

If you clicked Don’t Allow when macOS asked, the window says “Joiner for DJI couldn’t read Downloads. You can allow it in System Settings > Privacy & Security > Files & Folders, then try again.” Click Open System Settings, turn on the folder for Joiner for DJI, then click Try Again.

Nothing to Join

The scan found nothing the app can join. Check that you picked the right card or folder. A DJI drone keeps its videos in a folder like DCIM/100MEDIA. The sentence under Nothing to Join says what was found instead.

Not enough space

The bar says how much the joins need and how much the disk has, and the Join button stays off. Untick something, choose another disk with Change…, or make room on the disk.

A card formatted as FAT32 can’t hold a file over 4 GB, so the app refuses to save a bigger joined file there and asks you to choose another disk.