Google's Android developers have been tipped about a software bug which results in abnormally high CPU usage when using the Nexus 5's camera. A developer chimed in on Google's bug tracker, saying that the company has fixes ready for a future maintenance update. He explained that a recent update to Skype makes the app access the camera regularly (in the background) in a way that triggers high CPU usage. This results in battery drain, slowdown, and inability to access the camera app.
The googler believes that this isn't a bug in Skype itself, and other apps which handle camera data through a specific Android process can also cause the bottleneck. The developer could not provide an estimate for a maintenance update's release. Until it's ready, he suggested rebooting the phone to resolve the problem temporarily. Uninstalling Skype is also a good option, at least for the few of you who can get by without it.
The programmer also said that the problem might appear in other KitKat-running devices that have the same Qualcomm imaging chip as the Nexus 5, but it will be up to their respective manufacturers to issue fixes due to differences in software.
For reference, here's the full quote from the developer:
We believe we have fixes for the current high CPU reports on N5 due to mm-qcamera-daemon, and they will be included in the next maintenance update. At this point, we don't need more reports of the problem, with some exceptions I'll detail below.
We've had scattered reports of persistent high CPU usage of mm-qcamera-daemon since our last maintenance update, and based on those, found a number of bugs that were then fixed.
More recently, there's been a significant increase in the frequency of reported problems. These may be related to a recent update to Skype, which seems to access the camera regularly from its background service in some way that triggers this bug (note, we don't currently believe there's a bug in Skype itself). Investigating this, we've identified a few additional fixes that we hope resolve this issue for good. However, since the high CPU usage is an intermittent problem, we're continuing to test our fixes to verify the problems are gone.
Unfortunately, I can't provide an estimate for when the maintenance update will be ready, due to all the testing we need to do for this and other fixes. Until then, rebooting the phone is the only way to stop the high CPU usage/lack of camera function once it starts.
Uninstalling Skype may substantially reduce the likelihood of this bug appearing, but I realize Skype is a very important application for many people. Other camera-using applications may trigger this bug as well, but that's been relatively rare. Most applications also do not access the camera when not in the foreground, so they will only trigger issues when actively used.
I'd also like to note that instances of high CPU use of mm-qcamera-daemon on other devices besides the N5 need to be reported to their manufacturers - while those devices also use a Qualcomm chip for their camera processing (and thus have a mm-qcamera-daemon process), each has differences in their software and issues with them do not necessarily mean the N5 has the same problem, and vice versa.
If you are seeing high CPU use of mm-qcamera-daemon, and you have not used the camera at all, or installed an application like Skype that has a background service that accesses the camera (typically, applications that provide video chat may do this), we would like to know about it.
Otherwise, for Skype and other typical camera applications, we believe we have fixes identified, and you don't need to add more information to this bug - remember, any note added here will send updates to dozens of people.