private void startDecoderThread() {
        stopDecoderThread(); // To be safe

        if (decodeMode != DecodeMode.NONE && isPreviewActive()) {
            // We only start the thread if both:
            // 1. decoding was requested
            // 2. the preview is active
            decoderThread = new DecoderThread(getCameraInstance(), createDecoder(), resultHandler);
            decoderThread.setCropRect(getPreviewFramingRect());
            decoderThread.start();
        }
    }
Stop decoding, but do not stop the preview.
zxing-android-embedded/src/com/journeyapps/barcodescanner/BarcodeView.java