Here's a file demonstrating the problem

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Assigning it to me since bringert@ is not a project member.

I looked at the AVCaptureDevice docs (https://developer.apple.com/documentation/avfoundation/avcapturedevice?language=objc) to figure out which of the MediaTrackSettings (https://w3c.github.io/mediacapture-image/#mediatracksettings-section) could be implemented.

DOMString whiteBalanceMode;
double colorTemperature;

Looks like these can be implemented with 
https://developer.apple.com/documentation/avfoundation/avcapturedevice/1386369-whitebalancemode?language=objc (iOS 4.0+, macOS 10.7+) and friends.

DOMString exposureMode;

https://developer.apple.com/documentation/avfoundation/avcapturedevice/1388858-exposuremode?language=objc (iOS 4.0+, macOS 10.7+) should be usable for setting exposureMode.

In manual mode, https://developer.apple.com/documentation/avfoundation/avcapturedevice/1624606-exposureduration?language=objc needs to be set to control exposure time. But it's not clear from https://w3c.github.io/mediacapture-image/#mediatracksettings-section how to actually control "manual" mode exposure. Maybe there needs to be an exposureTime member in MediaTrackSettings?

DOMString focusMode;
double focusDistance;

See https://developer.apple.com/documentation/avfoundation/avcapturedevice/1389191-focusmode?language=objc (iOS 4.0+, macOS 10.7+) for setting focusMode

focusDistance can be read with https://developer.apple.com/documentation/avfoundation/avcapturedevice/1624643-lensposition?language=objc and set with  
https://developer.apple.com/documentation/avfoundation/avcapturedevice/1624617-setfocusmodelockedwithlenspositi?language=objc but these APIS seem to be limited to iOS 8.0+

sequence<Point2D> pointsOfInterest;

There is
https://developer.apple.com/documentation/avfoundation/avcapturedevice/1385853-focuspointofinterest?language=objc and
https://developer.apple.com/documentation/avfoundation/avcapturedevice/1388777-exposurepointofinterest?language=objc, but it's not clear from the MediaTrackSettings docs how to indicate what pointsOfInterest is for. I guess we'd just have to use MediaTrackSettings.pointsOfInterest to set both AVCaptureDevice focusPointOfInterest and AVCaptureDevice exposurePointOfInterest.

double            exposureCompensation;

Probably https://developer.apple.com/documentation/avfoundation/avcapturedevice/1624651-exposuretargetbias?language=objc (iOS 8.0+) and https://developer.apple.com/documentation/avfoundation/avcapturedevice/1624637-setexposuretargetbias?language=objc (iOS 8.0+)

double            iso;

https://developer.apple.com/documentation/avfoundation/avcapturedevice/1624649-iso?language=objc (iOS 8.0+)

double            brightness;
double            contrast;
double            saturation;
double            sharpness;

These seem like postprocessing options that aren't supported by AVCaptureDevice. Maybe that can be done with some other part of AVFoundation.

double            zoom;

https://developer.apple.com/documentation/avfoundation/avcapturedevice/1624611-videozoomfactor?language=objc (iOS 7.0+)

boolean           torch;

See https://developer.apple.com/documentation/avfoundation/avcapturedevice/1386035-torchmode?language=objc (iOS 4.0+ macOS 10.7+)

Nothing on this issue is Google confidential. Adding allpublic to open access.