If you're in a web page with a player the track you are playing is probably located within the page somewhere. That's true even when you're using a remote playlist, and even when the player is not Yahoo! Media Player.
Wherever the track is anchored, there's usually something which explains what it is. If it's a song this might say the title, artist name, and album name. If it's a podcast or videoblog there might be an episode number or date, a title for the blog entry, maybe show notes describing the theme, an explanation of who the interviewee is, that kind of stuff. There is often an image associated with the media; for example album art, a poster frame, or a photo of an interviewee. This info is usually an unstructured blob of text rather than structured metadata, but that doesn't mean the info is useless. To the contrary: it is very rich in comparison to the normal metadata you'd get in a desktop media player. Because it is so rich it's impossible for us to pull it all into the player for display next to the track controls. And why should we even try? Web pages exist for the sole purpose of carrying out this task, so the player shouldn't attempt to duplicate their functionality. What we should do instead is point the user to the relevant location in the page.
Find In Page shows you where the current track is in the page.
When you hit this button, the player scrolls the page so that the source of the current track is at the center of the screen. It also temporarily changes the play/pause button in the text to an animated gif which draws your eye to the right place.
To take this feature out for a spin, go to Ian Roger's blog (which has the unstable development version of the player, which you need because the feature isn't in the stable public build at the time of this writing), wait for the player to appear (which can take a little while, and yes we know about the performance problem), open the player all the way (which takes two clicks, and yes we are working to turn this into one click), and hit the
Find In Page button. Then open the playlist, select one of the songs further down (which will be buried far below the fold), and hit the button again.
What's interesting about this button is that it is a solution to a problem which doesn't exist in desktop media players. Old school players either have metadata or they don't, and if they do it is structured enough to be displayed in the player. In the browser there is no common way to do metadata, though the hAudio microformat may eventually fix that. Even if there was a way to do it, structured metadata in fields in a player will never equal the expressive power of plain old HTML. HTML has color, imagery, and some control over fonts. It can have social features. It can link to related documents. It can embed widgets with dynamic data or display interactive star maps. Metadata in an old school media player is just a spreadsheet.
The original HTML for a link is also within the flow of the page, so it shows the context of the media within the overall document. Context can carry info about chronology, about the person who selected the media, about the reason the media was selected, and a million other things that are good to know. Carrying all this information is something an old school media player can never do, but it's something which browsers excel at. Audio and video are being absorbed into a new hybrid medium, and the "Find In Page" feature is part of this migration of media from audio or video files in isolation to audio and video integrated into web pages as a whole.