Steps
1. In Twitter apps, Tap a Share icon in the lower-right .
2. Tap a Share Tweet via...
3. Tap a CopyLink icon.You can copy link of Twitter video you want to download.
4. In Web Browser,open the page of Twtitter Video Downloader.Paste the link you just copied into the Text Box,then tap or click the Start button.
5. Tap or click the DOWNLOAD button.The Video will open in a new tab.
[for iPhone] First you'll need to get the Dropbox app.
Tap the ✖ in its upper-left corner to close video.
Tap the Share icon at the bottom-center on the screen.
Tap the Save to Dropbox icon.You can save the video to Dropbox.