As part of the continuous evolution for the Online service platform, Microsoft has released two new specific features for Sharepoint Online.
PDF Viewing within the browser – PDF documents stored within Sharepoint can be viewed directly in browser – there is no need to download PDF files to your desktop to view. This will require the Adobe Acrobat plugin.
Streaming Large MP4 Files – MP4 Video files stored in a Sharepoint Online Library can be streamed much faster without the need to download the file first.
More Information of these updates can be found here