If you dont want to see any autoplay videos and GIFs on your account timeline or anywhere on twitter then you can disable it by doing some simple changes. To disable this feature in desktop, tap on your profile pic and choose Settings that located at the top the page. Next Scroll down to the Content section and Uncheck Video tweets. Save it by clicking on Save Changes button and you are done.
For IOS devices, go to the Me tab and click on gear icon at the lower right corner and tap Settings. In General section of Settings, you will see Video Autoplay option. You can select whether you want to play videos on Wifi only or Never want to play video automatically. Click on Done to save settings.