Does Video HDR affect only the preview or also the captured image?

Question

AVCaptureDevice has a property called isVideoHDREnabled. Does it affect only the preview, or also the captured image? The documentation doesn't say.

I would like my app to automatically take HDR images if iOS determines that it's warranted for the scene being photographed. Is there any downside to enabling it when supported?

I understand that this isn't supported on all device/camera combinations. The question is what it does when it is.

Answer 1

Quoted from the Apple developers guide (iPhone 6/ iPhone 6 Plus):

Single-Shot (Video) HDR

AKA “streaming HDR” or “video HDR”. The iPhone 6 and 6 Plus support continuous, streaming high-dynamic-range video as opposed to the more traditional method of fusing a bracket of still images with differing EV values into a single high dynamic range photo. The HDR support is built right into the sensor. This capability is referred to as “Video HDR” in the API. All AVCaptureDeviceFormat objects for the front-facing camera support video HDR. On the back-facing camera, the 540p30, 720p30, 1080p30, and 1080p60 formats support video HDR.

So is not only previewed, also the HDR video content is saved. As far as I understand, there should be not downsides in the HDR Single-Shot / Video HDR Formats, but as you can see in your documentation link tables, not highest resolutions are supported in HDR mode (VHDR), so you'll have to choose between the advantages and drawbacks of sacrificing resolution to improve the dynamic range.