I used the summarizer to summarize this video (it's a webinar replay, I snagged the CDN link):
https://dt9xom8irs6kr.cloudfront.net/u202642/1400016-123699939588596388.mp4
It gave me a great summary. However, when I clicked on the Discuss Further button, this now redirects to a new Assistant thread instead of the Discuss Doc tool. Assistant could not read the video, replying "We are sorry, we are not able to extract the source." (this was Claude Sonnet 4, if it matters)
I'm not sure what pipeline is in place for providing Assistant models with the content of video files like this, but this appears to be a regression from the original Discuss Doc tool, which would be able to answer questions about it.