What's CMML? ------------ This is an implementation of the Continuous Media Markup Language (CMML) for VideoLAN. In short, CMML is a (XML) markup language for time-continuous data, which of course includes multimedia such as video and audio. It allows one to annotate a media file with both structured and unstructured textual data, but one of its distinguishing features--and what this code implements--is its support for embedding hyperlinks in media files. So, while viewing some media (e.g. a radio interview with a band), you could provide a hyperlink to any URL, including a standard web page or other media (e.g. the band's home page). The hyperlinks are active only for specific intervals of time while the media is playing, so for example during a radio interview, the hyperlinks can change depending on what questions the interviewer is asking and topic is being discussed. For more general information on CMML and its role in the bigger picture of extending the World Wide Web to properly support multimedia, see . For specifications of CMML, see . Usage ----- Once you have hyperlinking capability, you take on some of the capabilities of a web browser, in particular following hyperlinks, and also maintaining a browsing history where you can go backwards and forwards between pieces of media you've linked to. So, if you are viewing a file with CMML markup: * Hyperlinks are displayed as a subtitle track * Hyperlinks are followed with the VLC "activate" hotkey (by default, this is just the Enter key) * Going back and forward are done with the "history-back" and "history-forward" keys, by default Cmd-[ and Cmd-] on Mac OS X, and Ctrl-[ and Ctrl-] on all other platforms. Until the media browsing history features are made available outside of the CMML plugin, you can only use the history features while viewing a file that contains CMML markup: e.g. you cannot navigate backwards or forward in the history while viewing a standard MPEG video. This is a limitation which may be removed if the media browsing code is merged into the VLC core. Overview of the code -------------------- First: a lot of this code could be implemented, or should be implemented, in VLC's core (libvlc) rather than be part of a codec plugin, either because it's something which really should belong in the core (e.g. media browsing history, system-indepedent interface to web browser) or a generally useful thing outside of the codec plugin (e.g. XML parser, URL handling library). That's well and good, but changes to libvlc are far-reaching and affect all of VLC, rather than only affecting a single plugin. It's sensible to gradually merge this stuff into libvlc on an as-needs basis, rather than trying to refactor out huge amounts of code at once. Here's a quick overview of what the files do: * browser_open.[ch]: A very simple attempt to provide a way to open the system's web browser. * history.[ch]: Media browsing history (as described above in "Usage"). * xstrcat.h: Simple wrapper around strcat(1) which performs a realloc(1) if needed. * xarray.[ch]: extensible (growable) array, similar to a Vector in Java/C++. Could be replaced with a vlc_list_t from libvlc's src/misc/objects.c if the vlc_list_t API were made public. * xlist.[ch]: Yet Another Linked List implementation (sorry guys :), only here because XTag (see below) uses it internally. * xtag.[ch]: A very simple (but working!), lightweight XML parser. * xurl.[ch]: A small URL handling library. * cmml.c: The actual 'codec' parser, which parses the CMML data (demuxed from the incoming media stream, of course), and provides two VLC vars ("psz-current-anchor-description" and "psz-current-anchor-url") which enable intf plugins to display the CMML data to the user and let them interact with it. * intf.c: Enables media browsing functionality by displaying hyperlinks as a subtitle track, and responding to user keypresses for following hyperlinks and navigating the media browsing history. So, all the files except for cmml.c and intf.c could be made available and re-used outside of this plugin, but currently are not (for the reasons given above).