In the case of auto, WhatsApp will detect the best compression algorithm for that specific video.
WhatsApp has started testing a new feature that lets users share videos in high quality. The name of the feature is 'Video Upload Quality' and it's currently under development, hence it's not available for the public.
According to The Verge, the feature will be available for users in a future update. This new feature has been currently released as part of WhatsApp Android Beta version 188.8.131.52.In a future update, users will be able to choose the video upload quality by picking one of 3 options, namely, Auto (recommended), Best Quality, and data saver.
In the case of auto, WhatsApp will detect the best compression algorithm for that specific video. Then another feature is the best quality one that lets WhatsApp always send the video using the best quality available.
There's also the data saver option that's enabled in Android settings and allows WhatsApp to compress videos before sending them. This new feature will come in handy to users as WhatsApp users currently don't have the option to select the quality of videos before sharing them with their contacts.
As per The Verge, in other WhatsApp-related news, it has been recently reported that WhatsApp is testing a new privacy feature that allows users to send media that has the ability to disappear once the receiver has seen the message.