TwitterInAnApp uses a 3rd party browser component called Chromium (part of the Google Chrome Embedded Framework project).
This component is the barebones browser, with a few additional supporting files to support the basics of Web Browsing where there are components containing FREE (not paid for) licenses for rendering images / video etc.
Unsupported images/video content are usually protected by licenses which requires a royalty or license fee to be paid to the holders of the Codec / Protocol rights. Providing support for these could be both time consuming and costly.
That’s not to say these won’t be supported in the future.
The Google Chrome project, and browser, has a financial backing meaning that the appropriate licenses have been applied for and components built into the browser to support the appropriate formats.
There’s a distinct possibility that some components may be external to the browser and you might be able to copy the files into the application directory for TwitterInAnApp. It’s a long shot though!