Thanks for getting back to me. I am sorry I was not more clear in my question.
In the article by Amy  (Community Manager) that is referred to in the title of this question , there is a section called “Watch this: Enjoy enhanced video loading and playback.” She says, “You can also preview videos with larger file sizes…”
I followed the only link provided for more information <Learn how to use our new video enhancements>  which took me to “How to play video and audio files in Dropbox.” The link there for <Video and audio playback FAQs>  has a link to <Learn about supported file types that can preview in Dropbox> . In the section describing “File types that preview as a video,” it says that for the preview to work, the “file must be smaller than the size limit listed in the chart.”
The chart shows different file types, but nothing about size limits:
.3gp .m2t .mpg .vob
.3gpp .m4v .mts .webm
.3gpp2 .mkv .mxf† .wmv
.asf .mov .ogv
.avi .mp4 .rm
.dv. .mpeg .ts
Thus my original question: What are the size limits for video files to preview?
(BTW, there is nothing in the first information link that is provided in the article  about any of the other “new video enhancements” that are described: fast forward and rewind controls, closed captioning, read transcription, new scrubbing features, etc..)