NotReadableError: Failed to allocate videosource

NotReadableError is the spec compliant error thrown by Firefox when webcam access is allowed but not possible.

Most commonly this happens on Windows because the webcam is already in use by another app. Firefox will throw this error on both Windows and Mac even though only on Windows processes get exclusive access to the webcam.

The error can happen for other reasons:

Although the user granted permission to use the matching devices, a hardware error occurred at the operating system, browser, or Web page level which prevented access to the device.

Chrome throws TrackStartError instead. It also throws it for other reasons. Chrome tabs can share the same device.

Source: common getUserMedia() errors .

Please make sure your camera is not been used by some other application (chrome, ie or any other browser).I wasted half my day searching for a solution, and in the end, found out my camera was used by other application.

I've encountered same issue on Windows 10, no other apps using my video device. The problem was that in Windows 10 in Settings->App permissions (in left column) there is a setting for microphone and camera (Allow apps to access your mic/camera) which needs to be turned on. It does not matter that you don't find your browser in app list below this setting, just enable it here and voila.