Originally Posted by GerryTJ

To upload and Tweet a video on twitter.com:
Click the Tweet button.
Click Add media.
Choose a video file stored on your computer and click Open.
Note: You?ll be prompted if the selected video is not in a supported format. Maximum file size is 512MB. See here for more details about formats.
In the Edit window, you can trim the length of your selected video between 1 and 30 seconds.
Note: Maximum video length is 30 seconds.
Click Done when you?re finished with your edits.
Complete your message and click Tweet to share your Tweet and video.

Originally Posted by jerkules

Tweet then media.