Introduction (1) (sorry, no cool logo/graphic yet, ideas?) GStreamer is a library and set of tools to build arbitrary, reconfigurable filter graphs. It derives from the OGI Pipeline and DirectShow (docs, no experience), and is in its second generation (first was completed/abandonded *in* Atlanta on the way to the Linux Expo). 0.1.0 release is scheduled for Oct 31, 1999. Will cover Background, Goals, Design, and Futures Why do we need this? launch reads the command line to create the graph, from .so's Connections (queues) are made by launcher, lots of switchout code Argument handling is messy, at start-time only ...thus there is basically only one state: running There is no real master process capable of seeing the whole pipeline as a graph, so wiring A->B->C with some backchannel (parameter, not data stream) from C to A is hard Channels try to do IPC, file, and network I/O, excess abstraction Goals (1) Provide a clean way to both build graphs and write new elements Make things easier by providing auto-connect, stock sub-graphs Include tools sorely lacking in OGI pipeline, like editor, saves Enable Linux to catch up with M$'s world, allowing commercial plugins to a stable API (as of 1.0) so we don't end up with N wheels from N-M different people (multiple projects) Overview (1) Object hierarchy capable of run-time discovery, based on GtkObject Deeply nested parent-child relationships enable threads, blackboxes Buffers can point to anything, are typed, and can carry metadata Plugins can be loaded at any point, and registry reduces loads Symbiotic editor lets you design/run/save graphs visually What are filter graphs? (1) Filters take data in and spit data out, doing something to it Filters have N>=0 inputs and M>=0 outputs Filter graphs are many filters connected together, like a circuit The goal is typically to move data from 'left' to 'right', towards some kind of user-visible conclusion, i.e. audio or video Architecture (3?) - Graphs of Elements (here lies screen-grab from editor) Element is core Object, Bins hold (and are) Elements Pads are fundamental to an Element, are cross-wired with pointers Since Bins hold Elements, and Bins are Elements, Bins hold Bins 'Ghostpads' provide interfaces for Bins without native interfaces # Threads are type of Bin that actually run in separate threads - States (table of states, invariants, and descriptions) COMPLETE Element has all needed information RUNNING Element has acquired resources, ready to go DISCOVERY ... (unimplemented) PREROLL ... (unimplemented) PLAYING Element is actively trading data PAUSED Special state where things just don't run (?..) States are used to keep elements in check - Buffers Buffers designed to be versatile, with arbitrary typing/metadata Has pointer to data, length, so can point to someone else's data Type system (crude so far) ensures buffers don't go stray Metadata can be attached, such as the audio parameters Ref-counting and copy-on-write avoids most copies, not complete Sub-buffers can be created from bigger buffer, limitting copies Gtk+ Object System (2) - Pros C-language object system, well tested (Gtk+, Gnome...) Arguments of any fundamental type, read/write, built-in hooks Signals used for hooks into object events, overridable Run-time discovery of args, signals (quarks) - Cons No multiple-inheritance, though I haven't *needed* it There are some holes (can't attach quarks to *eveything*) - Design Classes, instances are structs; 1st item is parent class Type system allows clean casting, ^^^^^^ Arguments are set/get by string, use functions to do the work, thus setting an arg might trigger a redraw of the GUI Signals are strings, use marshallers, various firing methods Basic GStreamer objects (1) - Elements (show class,instance structs) Very simple, just provides a means to handle pads, state - Bins (show class,instance structs) Supports children, handles group state transitions Pads (1) Pad list type, direction, and chaining function ptr When creating a sink pad (!src) you set the chaining function gst_pad_connect() sets the peers, and copies chain function to src Passing buffer to a src pad transparently calls the chain function (graph goes here...) Sources (1) Source provides functions to push data Regular push() function just takes next N bytes and sends them Async push_region() grabs N bytes at offset O and sends them EOF signal [will] reset the state from PLAYING down to !RUNNING "location" argument is global by convention, for filenames...URIs Connections (1) Special type of Filter that Threads (1) Special case of Bin that actually creates a thread transparently When RUNNING, thread exists, mutex/cond used to go [!]PLAYING Automatically determines how to start sub-graph Looks for both Sources and Elements wired to Connection Will cooperate with Pipelines when threading is not available Typing and Metadata (1) - Types Based on MIME types, set up as quarks, and dealt with as int Usable entirely at run-time, since they're registerable by plugins - Metadata Also registered as an int, but must be compile time due to structs Have refcounts and CoW semantics, since they travel with buffers Plugins (1) Plugin architecture designed around class system Arguments and signals provide interface over standard base class Each Element defined by ElementFactory, which is queried by name At plugin load, any number of ElementFactories and Types registered Element registers against Type as source or sink Editor (2+?) (show filter graph snapshot, a different one, more complex) Built as a parallel object hierarchy on top of GNOME Canvas Every object in filter graph has equivalent in editor, plus some Canvas is designed with groups and signal-propagation, so... Why not build the whole thing as subclasses of CanvasGroup? ...because updates get messy/recursive (the way I *was* doing it) Solution is to modify objects so they own Group rather than being Relatively trivial modification, but requires lots of repointering Still a genealogical mess of parents and children... XML The goal is to use XML heavily, with an eye towards DOM Used for both saving and providing pre-build components Both graph and editor will have namespace, they'll interleave A generic save function will exist for Elements, with hooks Saving an EditorElement will also save Element Also used for a plugin registry, to avoid loading all plugins leaky bucket is trivial applications - generic conferencing tool (repluggable codecs), mixing environment (data flow graphs)