Camera frames in a service / background process
android, android-camera, android-service
Solution
You can send the preview to a SurfaceTexture instead (`setPreviewTexture()`). This won't disappear when the app is paused. Requires API 11+.
You can see various applications of this technique in Grafika, which is generally doing video or GLES manipulation rather than stills, but the idea is similar.
Problem
For scientific measurements, I would like to access the camera frames from a service. The idea is to analyze the images coming from the camera in real-time under some conditions. Since the phone might be restarted or simply locked, it should be possible to start the process from a service. For now, I was satisfied by using a `Camera.Callback` and the `onPreviewFrame` callback, but it appears that it only works if my application is running in foreground. More precisely, the camera requires a valid `SurfaceView` in order to call the `onPreviewFrame` function. And a `SurfaceView` created in an Activity is destroyed when the activity is minimized / finished. I just cannot find a way to get the frames from a background process. Actually, it works on a `Galaxy Note 10.1`, but the `Galaxy S4` requires a valid SurfaceView. Is there a way to achieve this? There are many topics about this on StackOverflow, but none worked for me.