Projector can display streaming video and audio media such as YouTube links when the device is connected to the internet. If you add a web link attachment to a plan item, and that web link points to a streaming media type that is supported by Projector, then Projector will stream and play the media when the slide is selected.
YouTube
You can attach a YouTube link to a plan item by using the PCO Services Files screen, by either adding a web Share link that you have copied from the youtube.com site (with the Link section of the Files screen), or by browsing for the YouTube video within the YouTube section of the Files screen. Consult the PCO Services Uploading, Linking, and Creating Files help article for more information.
Vimeo
Projector can play a streaming Vimeo video, but only if it has been given a private link by the owner of the video (requiring a paid Vimeo plan). If you browse for a Vimeo video through the PCO Services Files screen (Vimeo section), Projector cannot play it, since it will require using an authenticated Vimeo player, which Projector does not support (nor does PCO Service's Media Player, for that matter). If you have access to a Vimeo private link, then you can add it via the PCO Services Files screen using the Link section. Consult the Vimeo Video privacy, explained blog post for more information.
Other Streaming Media (links)
Projector can also play any supported media type that is made available from a streaming server via a publicly available web link that requires no authentication to access. You add those links to a plan item via the PCO Services Files screen using the Link section.
Copyright Issues
Protecting the copyright of the media file owners is an important thing to consider when using streaming media, since it is likely that such media will not be covered under the general Copyright releases of services like CCLI. Please consult the PCO Services Copyright Concerns help article to guide you in better understanding Copyright issues.