Apple specifies the external drive for iPhone ProRes recording in four ways: it must be formatted with exFAT, it must not be password-encrypted, it must be connected with a USB 3 cable rated at least 10 Gbit/s, and it must sustain a write speed of at least 220 MB/s for 4K60 ProRes or 440 MB/s for 4K120 ProRes.
Those are not guidelines. They come from Apple's own ProRes support article, and the drive-speed one has a visible failure mode: "If you attach a slower external storage device, you might get a Slow Recording Speed message."
The requirements, at a glance
Every cell below is Apple's wording from About Apple ProRes on iPhone.
| Requirement | What Apple specifies |
|---|---|
| File system | "Your external storage device must be formatted with exFAT." |
| Encryption | "Password-encrypted drives aren't supported." |
| Cable | "Use a USB 3 cable with speed of at least 10 Gbits per second." |
| Write speed, 4K60 ProRes | "at least 220 MB per second" |
| Write speed, 4K120 ProRes | "at least 440 MB per second" |
| Power draw | Apple's footnotes pair each speed tier with a drive that supports "maximum power draw of 4.5 W" |
| Before each 4K120 session | "You must reformat your external storage device before beginning each 4K120 ProRes recording session to ensure optimal performance." |
| Free space on the iPhone | "you need at least 10 percent of your device's storage to be free" |
Two of these get skipped constantly when people shop for a drive.
The first is the reformat rule. Apple does not say "format it once." It says you must reformat before beginning each 4K120 session, "to ensure optimal performance." That turns the drive into a working scratch disk rather than an archive: whatever you shot has to come off it before the next 4K120 take.
The second is power draw. The speed footnotes name 4.5 W alongside the MB/s figure, so a drive's spec sheet has to satisfy both halves. Bus-powered enclosures vary a lot here, and a drive that meets the speed number is not automatically inside the power number.
Why an external drive is in the picture at all
ProRes is enormous compared with what the phone normally records. Apple's one comparison is: "ProRes files are up to 30 times larger than HEVC files." Note the "up to" — that is a ceiling, not a multiplier you can apply to a clip and get a prediction.
The ProRes support article and the user guide's ProRes page do not give a per-minute megabyte figure at any resolution, so if you need a storage budget, check the official documentation and measure a short test take yourself rather than trusting a number from a forum.
Internal recording is also capped by the phone's own storage tier. Apple's table ties resolution and frame rate to capacity: a 128 GB device is listed at 1080p HD at 30 fps and 25 fps, while 256 GB, 512 GB, 1 TB and 2 TB models add 1080p at 60 fps and 4K at 30, 25 and 24 fps. The user guide states the 128 GB case bluntly: "On iPhone 15 Pro models and iPhone 16 Pro models with 128 GB, recording to internal storage is only available at 1080p at 30 fps."
The high frame rates are where external recording stops being optional. Apple's user guide says "iPhone 16 Pro models, iPhone 17 Pro models, and iPhone 18 Pro models can record 4K at 120 fps when connected to a compatible external storage device," and the iPhone 17 Pro tech specs list ProRes as "up to 4K at 120 fps with external recording."
What to do when the drive can't keep up
If you are seeing Slow Recording Speed, work down this list in order.
- Check the format, not just the speed. exFAT is required. A drive that arrived formatted for a Mac or a PC's default file system meets neither the letter of Apple's requirement nor, in the 4K120 case, the reformat-before-each-session rule.
- Check the cable. Apple specifies the cable separately from the drive — at least 10 Gbit/s, USB 3. A charge-oriented cable in the bag is the single cheapest thing to rule out.
- Drop from 4K120 to 4K60. The requirement halves, from 440 MB/s to 220 MB/s. If the drive was marginal, this is the difference between a usable take and a warning.
- Record internally at a rate your capacity supports. Consult the resolution-and-capacity table above before you assume the phone will take it.
- Turn ProRes off for the shot you do not need it for. Apple: "If you turn ProRes off in the Camera app, the video format defaults to either High Efficiency Video Coding (HEVC) or Most Compatible (H.264). To set this format, open Settings, tap Camera, tap Formats, and then choose a format."
Delivery is a separate problem from capture. A ProRes master is not something you hand to a client over chat, and Apple notes what happens if you try to open it somewhere unsupported: "Apps might transcode a ProRes video to a smaller H.264 format if ProRes isn't supported." If you are going to end up with an H.264 copy anyway, it is better to make that copy deliberately, with control over resolution and bitrate, than to let an unknown app decide.
Try it right here
Runs in your browser. Your file is not uploaded anywhere.
This runs entirely inside your browser tab — the file is read from disk, re-encoded locally, and handed back. Nothing is uploaded, which matters more than usual when the source is a multi-gigabyte camera original. If you only need the container changed rather than the whole file re-encoded, MOV to MP4 covers that case, and compress video gives you the manual controls instead of a preset.
Model, mode and version gotchas
You need iOS 15.1 or later. Apple's requirement line reads: "To use Apple ProRes, you need iOS 15.1 or later and one of these iPhone models:".
The two official pages list different models. The support article's model list starts at iPhone 17 Pro Max and iPhone 17 Pro and does not include iPhone 18 Pro. The user guide's ProRes page does cover iPhone 18 Pro, including a first-run step: "To turn on Apple ProRes on iPhone 18 Pro models, tap Configure Pro Video Storage, set the amount of storage to reserve, tap Update Pro Video Storage, then tap. You only have to do this the first time you turn on Apple ProRes." The same split shows up at 4K120: the support article's table marks that row "iPhone 17 Pro models and iPhone 16 Pro models only," while the user guide includes iPhone 18 Pro. Treat the user guide as the newer of the two and open both before buying hardware.
Non-Pro iPhones are not in this conversation. The iPhone 17 Pro tech specs list "Video formats recorded: HEVC, H.264, ProRes, and ProRes RAW"; the iPhone 17 specs list "Video formats recorded: HEVC and H.264." The port differs too — USB 3 up to 10 Gb/s on the Pro, USB 2 up to 480 Mb/s on the non-Pro.
Three capture modes are excluded. Apple states it twice, in near-identical words: "You can't use ProRes with Cinematic mode, slo-mo mode, or time-lapse video," and, in the user guide, "ProRes isn't supported in Cinematic, Time-lapse, or Slo-Mo mode."
Dynamic range options differ by generation. Apple: "iPhone 15 Pro models, iPhone 14 Pro models, and iPhone 13 Pro models support ProRes recording using the built-in storage of your iPhone in high dynamic range (HDR), in standard dynamic range (SDR), or in Log encoding. iPhone 17 Pro models and iPhone 16 Pro models support ProRes recording in either HDR or in Log encoding."
FAQ
What write speed does an SSD need for iPhone ProRes? At least 220 MB per second for 4K60 ProRes and at least 440 MB per second for 4K120 ProRes, per Apple's ProRes support article. Apple's footnotes pair those figures with a maximum power draw of 4.5 W.
Does the drive have to be exFAT? Yes. Apple states the external storage device must be formatted with exFAT, and that password-encrypted drives aren't supported.
Do I really have to reformat the drive every time? For 4K120 ProRes, that is what Apple says: reformat before beginning each 4K120 recording session to ensure optimal performance. That sentence names the 4K120 session specifically; for other ProRes modes, check the official documentation.
How many GB per minute does ProRes use? Apple's ProRes pages give no per-minute figure. The only relative statement on them is that ProRes files are "up to 30 times larger than HEVC files" — check the official documentation for anything more specific, and shoot a test clip to size your own drive.
Why does my Mac or PC struggle with the resulting files? For ProRes RAW specifically, Apple points Windows users to a plugin: "To enable playback of ProRes RAW and ProRes RAW HQ video files in compatible applications on Windows systems, install Apple ProRes RAW for Windows." For everyday review copies, transcoding is usually the faster answer — the same logic applies to HEVC files that won't play in Google Drive.
More spec-and-limit breakdowns live in the limits section, and the full set of browser-based converters is at Clapr tools. Figures cited from Apple's ProRes support article and iPhone user guide, checked 16 September 2026 — Apple revises these pages, so verify against the official documentation before buying a drive.
