Resolution, frame rate and file size in dual camera video
Dual camera recording tops out lower than single-camera recording, and that is not an app being lazy. Two live camera pipelines share one hardware budget, so the settings you can pick are constrained by what the pair costs together, not by what one camera could manage alone. Understanding what each setting actually changes makes it easy to pick the right one.
There are three numbers worth knowing: the capture resolution of each camera, the size of the canvas they are composited onto, and the bitrate the result is encoded at. They are independent, and confusing them is where most of the confusion about “why is my dual video not 4K” comes from.
Capture resolution: what 720p and 1080p mean here
DualCam offers two capture settings, which select the format each camera runs at: 1280 pixels wide for 720p and 1920 pixels wide for 1080p. Both cameras are set to the same one, and both are locked to 30 frames per second so the two streams stay in step.
This is the setting that costs hardware budget. 1080p roughly doubles the pixel throughput per camera compared with 720p, and it is the setting most likely to be refused on an older supported device or dropped when the phone gets hot. On any long or important take, 720p is the setting that finishes.
Canvas size: what actually gets written
The composited canvas is a separate thing from the capture resolution. DualCam writes 1080 pixels wide, with a choice of two heights: 1920 for standard 9:16, or 2340 to fill a modern iPhone display edge to edge. That is the resolution of the video file you end up with, regardless of whether the cameras were capturing at 720p or 1080p.
Higher capture resolution therefore does not give you a bigger file — it gives you a sharper one, because there is more detail available to draw into the same canvas. This is especially visible in a picture-in-picture inset, where a small window is being sampled down from the source frame anyway, and in split layouts, where a quarter of each source frame is cropped away before it is drawn.
File size: about 75 MB per minute
DualCam encodes the composited video at approximately 10 Mbps using H.264 High profile. That works out to roughly 1.25 megabytes per second, or about 75 MB per minute of video — a little over 4 GB per hour. The audio track adds a mono AAC stream at 96 kbps, which is under a megabyte per minute and does not meaningfully change the arithmetic.
Because the canvas size is fixed, this rate does not change when you switch capture resolution. A minute of dual video costs about the same on disk at 720p and at 1080p; what changes is how much detail is in it.
Rough capacity, at a glance
DualCam requires at least 200 MB free to start a recording, and stops an in-progress recording when free space drops under 100 MB, so the last fraction of the disk is not usable recording time.
- 1 GB free ≈ 13 minutes
- 5 GB free ≈ 66 minutes
- 10 GB free ≈ 2 hours 13 minutes
Why not 4K?
A multi-camera session is not just two independent recordings. Every camera in the session must run a format that explicitly supports multi-cam, and the combined cost of all inputs must stay within a hardware budget. In practice that budget is what rules out the very high formats: the same phone that will happily record 4K from one camera cannot pay for two high-resolution streams plus a real-time compositing pass plus an encode of the result.
A dual-camera app that advertised 4K would either be shipping something that fails on most devices, or quietly redefining what the number means. Choosing an honest ceiling and behaving predictably at it is the better trade.
Which setting to use
- Short takes, good conditions, cool phone, plenty of space — 1080p, for the extra detail in insets and cropped split halves.
- Long takes, hot weather, an older supported iPhone, or anything you cannot reshoot — 720p. Finishing matters more than sharpness.
- Anything you will crop or reframe later — 1080p, because you are throwing away pixels afterwards.
- Anything destined straight for a short-video feed at phone size — 720p is genuinely hard to fault after platform re-encoding.
Common follow-up questions
Why is 1080p unavailable on my iPhone?
Because the resulting multi-camera configuration exceeded the hardware budget on your device. DualCam measures the cost after reconfiguring and reverts to the previous setting rather than letting the session fail. It is a per-device limit.
Can I change resolution while recording?
No. Resolution, mute and the countdown are locked once recording starts, because they determine how the output file is constructed. Layout, inset placement and filters can all be changed mid-take.
What format is the file?
An MP4 with H.264 video and, unless you recorded muted, a single mono AAC audio track. Nothing exotic — it plays and uploads everywhere.
Want to just do this?
DualCam records the iPhone front and back cameras at the same time and writes one finished MP4 while you shoot. Free, no account, no ads, nothing leaves the phone.