Aug 13 (Reuters) - Facebook Inc (FB.O) on Friday rolled out end-to-end encryption for voice and video calls on Messenger, adding another layer of privacy to its widely used communications platform. Facebook"s WhatsApp and Messenger services already have end-to-end encryption on personal texts messages sent by users. The social media giant has gradually been adding audio and video features to its portfolio of messaging services. These features have gained popularity in the past year as people sought to stay in touch virtually during the coronavirus pandemic. "We"ll also kick off a limited test with adults in certain countries that lets them opt-in to end-to-end encrypted messages and calls for one-on-one conversations on Instagram," Facebook said in a blogpost, adding that the security feature will also be tested in the coming weeks on Messenger"s group chats.