How to get camera preview frame after every 500ms

Question

I am developing sample application which gives me color code of pointed image or object via Camera in android. My application is similar to this application and I am using this

Answer 1

You can calculate the elapsed time in onPreviewFrame(). For example:

    boolean isFirstTime = true;
    long startTime = 0;
    PreviewCallback callback = new PreviewCallback() {
        @Override
        public void onPreviewFrame(byte[] data, Camera camera) {
            // TODO Auto-generated method stub
            if (isFirstTime) {
                isFirstTime = false;
                startTime = SystemClock.currentThreadTimeMillis();
                decodeYUV420SP(pixels, data, previewSize.width,  previewSize.height);  
                listener.OnPreviewUpdated(pixels, previewSize.width, previewSize.height);
            }
            else {
                long currentTime = SystemClock.currentThreadTimeMillis();
                long elapsedTime = currentTime - startTime;
                if (elapsedTime >= 500) { // trigger your event
                    startTime = currentTime;
                    decodeYUV420SP(pixels, data, previewSize.width,  previewSize.height);  
                    listener.OnPreviewUpdated(pixels, previewSize.width, previewSize.height);
                }
            }
        }
    };

Do not forget to reset the boolean value and start time when you switch the preview status.

Answer 2

Nothing will guarantee precise 500ms - camera hardware is not set to respond immediately. Still, you can be rather close to that. First of all, open the camera from a background Handler thread (see https://stackoverflow.com/a/19154438/192373).

public void onPreviewFrame(byte[] data, Camera camera) {
    long releaseTime = SystemClock.currentThreadTimeMillis() + 500;
    decodeYUV420SP(pixels, data, previewSize.width,  previewSize.height);  
    listener.OnPreviewUpdated(pixels, previewSize.width, previewSize.height);
    resetBuffer();
    SystemClock.sleep(releaseTime-SystemClock.currentThreadTimeMillis());
}

This assumes that decodeYUV420SP() and OnPreviewUpdated() together take much less than 500ms.