2 (sorry, no cool logo/graphic yet, ideas?)
3 GStreamer is a library and set of tools to build arbitrary,
4 reconfigurable filter graphs. It derives from the OGI Pipeline
5 and DirectShow (docs, no experience), and is in its second
6 generation (first was completed/abandoned *in* Atlanta on the
7 way to the Linux Expo).
8 0.1.0 release is scheduled for Oct 31, 1999.
9 Will cover Background, Goals, Design, and Futures
11 launch reads the command line to create the graph, from .so's
12 Connections (queues) are made by launcher, lots of switchout code
13 Argument handling is messy, at start-time only
14 ...thus there is basically only one state: running
15 There is no real master process capable of seeing the whole
16 pipeline as a graph, so wiring A->B->C with some backchannel
17 (parameter, not data stream) from C to A is hard
18 Channels try to do IPC, file, and network I/O, excess abstraction
20 Provide a clean way to both build graphs and write new elements
21 Make things easier by providing auto-connect, stock sub-graphs
22 Include tools sorely lacking in OGI pipeline, like editor, saves
23 Enable Linux to catch up with M$'s world, allowing commercial
24 plugins to a stable API (as of 1.0) so we don't end up with N
25 wheels from N-M different people (multiple projects)
27 Object hierarchy capable of run-time discovery, based on GtkObject
28 Deeply nested parent-child relationships enable threads, blackboxes
29 Buffers can point to anything, are typed, and can carry metadata
30 Plugins can be loaded at any point, and registry reduces loads
31 Symbiotic editor lets you design/run/save graphs visually
32 What are filter graphs? (1)
33 Filters take data in and spit data out, doing something to it
34 Filters have N>=0 inputs and M>=0 outputs
35 Filter graphs are many filters connected together, like a circuit
36 The goal is typically to move data from 'left' to 'right', towards
37 some kind of user-visible conclusion, i.e. audio or video
40 (here lies screen-grab from editor)
41 Element is core Object, Bins hold (and are) Elements
42 Pads are fundamental to an Element, are cross-wired with pointers
43 Since Bins hold Elements, and Bins are Elements, Bins hold Bins
44 'Ghostpads' provide interfaces for Bins without native interfaces
45 # Threads are type of Bin that actually run in separate threads
48 (table of states, invariants, and descriptions)
49 COMPLETE Element has all needed information
50 RUNNING Element has acquired resources, ready to go
51 DISCOVERY ... (unimplemented)
52 PREROLL ... (unimplemented)
53 PLAYING Element is actively trading data
54 PAUSED Special state where things just don't run (?..)
55 States are used to keep elements in check
58 Buffers designed to be versatile, with arbitrary typing/metadata
59 Has pointer to data, length, so can point to someone else's data
60 Type system (crude so far) ensures buffers don't go stray
61 Metadata can be attached, such as the audio parameters
62 Ref-counting and copy-on-write avoids most copies, not complete
63 Sub-buffers can be created from bigger buffer, limitting copies
64 Gtk+ Object System (2)
66 C-language object system, well tested (Gtk+, Gnome...)
67 Arguments of any fundamental type, read/write, built-in hooks
68 Signals used for hooks into object events, overridable
69 Run-time discovery of args, signals (quarks)
71 No multiple-inheritance, though I haven't *needed* it
72 There are some holes (can't attach quarks to *eveything*)
75 Classes, instances are structs; 1st item is parent class
76 Type system allows clean casting, ^^^^^^
77 Arguments are set/get by string, use functions to do the work,
78 thus setting an arg might trigger a redraw of the GUI
79 Signals are strings, use marshallers, various firing methods
80 Basic GStreamer objects (1)
82 (show class,instance structs)
83 Very simple, just provides a means to handle pads, state
85 (show class,instance structs)
86 Supports children, handles group state transitions
88 Pad list type, direction, and chaining function ptr
89 When creating a sink pad (!src) you set the chaining function
90 gst_pad_connect() sets the peers, and copies chain function to src
91 Passing buffer to a src pad transparently calls the chain function
94 Source provides functions to push data
95 Regular push() function just takes next N bytes and sends them
96 Async push_region() grabs N bytes at offset O and sends them
97 EOF signal [will] reset the state from PLAYING down to !RUNNING
98 "location" argument is global by convention, for filenames...URIs
100 Special type of Filter that
102 Special case of Bin that actually creates a thread transparently
103 When RUNNING, thread exists, mutex/cond used to go [!]PLAYING
104 Automatically determines how to start sub-graph
105 Looks for both Sources and Elements wired to Connection
106 Will cooperate with Pipelines when threading is not available
107 Typing and Metadata (1)
109 Based on MIME types, set up as quarks, and dealt with as int
110 Usable entirely at run-time, since they're registerable by plugins
112 Also registered as an int, but must be compile time due to structs
113 Have refcounts and CoW semantics, since they travel with buffers
115 Plugin architecture designed around class system
116 Arguments and signals provide interface over standard base class
117 Each Element defined by ElementFactory, which is queried by name
118 At plugin load, any number of ElementFactories and Types registered
119 Element registers against Type as source or sink
121 (show filter graph snapshot, a different one, more complex)
122 Built as a parallel object hierarchy on top of GNOME Canvas
123 Every object in filter graph has equivalent in editor, plus some
124 Canvas is designed with groups and signal-propagation, so...
125 Why not build the whole thing as subclasses of CanvasGroup?
127 ...because updates get messy/recursive (the way I *was* doing it)
128 Solution is to modify objects so they own Group rather than being
129 Relatively trivial modification, but requires lots of repointering
130 Still a genealogical mess of parents and children...
132 The goal is to use XML heavily, with an eye towards DOM
133 Used for both saving and providing pre-build components
134 Both graph and editor will have namespace, they'll interleave
135 A generic save function will exist for Elements, with hooks
136 Saving an EditorElement will also save Element
137 Also used for a plugin registry, to avoid loading all plugins
142 leaky bucket is trivial
143 applications - generic conferencing tool (repluggable codecs), mixing
144 environment (data flow graphs)