chrome://media-internals is a tool to dig into the guts of the Chrome audio/video stack.It currently displays 3 things:
MediaLog contains helper methods for creating MediaLogEvents, and ContentMediaLog implements its AddEvent() function to send a MediaLogEvent to the browser process as an IPC message. A single instance of MediaLog is associated with each WebMediaPlayer. This instance currently gets passed down to PipelineImpl and BufferedResourceLoader and can easily be handed off to other potential data sources (it’s RefCountedThreadSafe).
MediaInternals is a singleton attached to the IO thread. The IPC messages from ContentMediaLog get passed to it, and it handles notifications from AudioRendererHost. It lives in chrome/, but it implements the MediaObserver interface in content/, allowing AudioRendererHost and RenderMessageFilter (the IPC message handler) to call it.
MediaInternalsUI is a WebUI component that hosts chrome://media-internals. There’s not much of interest here, just lots of proxying function calls across threads.
chrome://media-internals contains most of the logic. It handles MediaLogEvents, NetLog events, and updates from AudioRendererHost. It infers the contents of the media cache from NetLog events (cache_entry.js, disjoint_range_set.js) and displays a log of events (event_list.js) and properties (media_player.js) of each active media player. I also displays time measurements between pre-defined events (metrics.js) and some basic information about audio streams from AudioRendererHost.