Allow to index transcriptions

### Describe the problem to be solved

I've been searching some transcription strings in Google from 6-8 months videos but I don't find them. I guess, for some reason, the transcriptions are not being indexed.

Is there a way to allow crawlers to index the transcription of a video? I think it would help a lot to find videos by its content.

Thanks.

### Describe the solution you would like

_No response_

The issue names no files, tests, or entry points. First clarify how transcription text is currently exposed to crawlers and what indexing behavior is expected; then trace the relevant transcription and video-page paths. Done means transcription strings from videos can be discovered through Google search.

Written by the indexing model from the issue text.