A ten-minute video on an iPhone always works. A ninety-minute one — a concert, a lecture, a rehearsal, a conference talk — fails often enough that most people who do it regularly have lost at least one.
The failures are not mysterious. There are five of them, and four are avoidable before you press record.
1. Storage: do the arithmetic first
Apple publishes the sizes, and they are on the phone in Settings → Camera → Record Video. Per minute, using HEVC:
| Setting | Per minute | 90 minutes |
|---|---|---|
| 1080p / 30 fps | ~65 MB | ~5.7 GB |
| 1080p / 60 fps | ~100 MB | ~8.8 GB |
| 4K / 24 fps | ~135 MB | ~11.9 GB |
| 4K / 30 fps | ~170 MB | ~15 GB |
| 4K / 60 fps | ~400 MB | ~35 GB |
When the disk fills, the recording stops — mid-sentence, with no warning worth the name. Check free space beforehand and leave a few gigabytes of headroom for the rest of the system.
For a talking head in a dark hall, 4K buys almost nothing. 1080p at 30 fps is the setting that survives.
2. Heat
Sustained 4K encoding, a bright display, and a warm room together push the phone into thermal throttling. Past a point iOS puts up the temperature warning and shuts the camera down.
What helps, roughly in order:
- Record at 1080p / 30 fps rather than 4K.
- Take the case off. A thick case is an insulator.
- Do not charge while recording if you can avoid it — charging and encoding at once is the worst combination.
- Keep it out of direct sun and off warm surfaces.
- Dim the screen. It is a heat source as well as a battery drain.
3. Battery
Ninety minutes of camera plus ninety minutes of bright display is a lot. Three things buy back real time:
- Dim or darken the screen. On OLED iPhones black pixels are nearly off, and the display is one of the biggest draws.
- Airplane mode, if you do not need the network. A phone hunting for signal in a concrete venue is expensive.
- A battery pack, with the heat caveat above — plug in before the phone gets warm, not after.
4. Interruptions
An incoming call ends the capture session. So does anything else that takes the camera, and so does the phone locking itself.
Before a long session: turn on a Focus mode or airplane mode, check that no alarm is due, and set Settings → Display & Brightness → Auto-Lock to Never. Put Auto-Lock back afterwards — it is easy to leave it that way for a month.
5. The file itself
This is the one nobody expects, and it is the one that turns a bad evening into a lost recording.
A .mov or .mp4 file is not readable until its index is written. With a plain
recorder, that index goes in when you press stop. Everything before that point is video
data with nothing to describe it — so if the app is killed first, by a crash or a flat
battery or a force quit, what is left on disk is a file no player will open. The bytes are
there. The map is not.
Two defences:
- Stop the recording yourself. Do not let the battery decide when the session ends. If the phone is at 5% and the encore is still going, stop, save, and start a new one.
- Use a recorder that writes in fragments. Some apps finalise a small chunk every few seconds instead of holding one file open for the whole session, so an interrupted recording leaves a playable file that simply ends early.
NoLight, the iPhone camera I built for long sessions in dark rooms, writes in five-second fragments for exactly this reason, and recovers whatever was completed if the app dies mid-recording. On a 135-second test the finished file was 0.053 seconds off the wall clock.
6. The screen, if you are in a dark room
The remaining problem is social rather than technical: a viewfinder at full brightness held up for an hour and a half lights up everyone around you.
The screen cannot be switched off while an iPhone records — that is an iOS limit, covered in Can an iPhone record video with the screen off? — but it can go dark while the app stays open, which solves the same problem and helps with items 2 and 3 as a bonus.
The checklist
Before a long recording:
- Free space ≥ the table above, plus headroom
- 1080p / 30 fps unless there is a real reason for 4K
- Case off, not charging, out of the sun
- Focus or airplane mode on, no alarms due
- Auto-Lock set to Never
- Screen dimmed or dark
- A recorder that survives being interrupted
- Stop it yourself when the battery gets low