In November of last year, the company began to roll out auto-captions on a limited scale, which use speech recognition to automatically transcribe what’s said in a video. And now, it’s going to enable the feature for all videos uploaded to YouTube where English is spoken.This move will engender a lot of goodwill for Google, and rightly so, for enabling deaf people to consume video content that they otherwise couldn't. Even if the transcription is poor (and I've seen some pretty bad transcripts from humans covering live events), it's better than nothing.
More importantly, this will give Google more text to scan and analyze. The system will have a better idea of what each video is about and therefore be better at suggesting related videos. It will also make it easier for Google to correctly target advertising based on the content of each video. More relevant advertising leads to higher clickthrough rates and more money for Google's bottom line.