Live automatic captions are slowly being rolled out to predicted English channels with over 10,000 subscribers. 

Automatic captions are shown on Android and iOS devices and on computers. To learn how to turn captions on or off, follow these steps.  

After the live stream ends, live automatic captions will not remain and automatic captions will be generated based on the video on demand (VOD) process. LASR is specifically for an in progress live stream.

Troubleshoot live automatic captions

If the stream doesn't show automatic captions, it could be due to one or more of the following reasons:

• The feature hasn’t been enabled for the channel, as we are slowly rolling out to channels with more than 10k subscribers.
• Channel is streaming in ultra low or low latency (such as a mobile live stream). Live automatic captions are only available for normal latency streaming. 
• The language in the video is not yet supported by automatic captions.
• The video has poor sound quality or contains speech that YouTube doesn't recognize.
• There are multiple speakers whose speech overlaps or multiple languages at the same time. 

* Nguồn: Youtube