1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
|
SOMEWHAT OUTDATED, design still holds though
--------------------------------------------
1. Introduction
---------------
The type system is used to attach meaning to the bytes in a GstBuffer.
A plugin can decide to add metadata to the GstBuffer, this metadata
will carry an associated typeid.
Types are also used by the plugins to expose the type of their pads to
the type system.
Types are essential for autoplugging.
We will explain the inner workings of the type system in this document, as
well as the API used in the plugins.
2. major types
--------------
major types are identified with mime types and are used to denote a
family of types.
More specific information about the type is given using properties. This
will allow us to be very specific without creating a lot of mime types.
3. API
------
Both a simple array based specification and a real API will be
provided to build the capabilities.
In the array based approach, we basically build an array of pointers.
Some macros will be available to specify ranges, boolean values, lists
and id's. (not sure if this can be done)
#define GST_TYPE_INT_RANGE(a, b) GST_TYPE_RANGE,(a),(b)
#define GST_TYPE_BOOLEAN(a) GST_TYPE_BOOLEAN,(a)
#define GST_TYPE_LIST(a...) GST_TYPE_LIST,(##a),NULL
for example:
static GstTypeCapsFactory mpg123_sink_caps[] = {
"audio/mp3",
"layer", GST_TYPE_INT_RANGE (1, 3),
"bitrate", GST_TYPE_INT_RANGE (8, 320),
"framed", GST_TYPE_BOOLEAN (true),
NULL
};
will expand to the array:
static GstTypeCapsFactory mpg123_sink_caps[] = {
"audio/mp3",
"layer", GST_TYPE_RANGE,1,3,
"bitrate", GST_TYPE_RANGE,8,320,
"famed", GST_TYPE_BOOLEAN,true,
NULL,
};
when we register the caps factory, the strings will be converted
into GQuarks and be stored into a GData Keyed Data List.
This will result in a GstTypeCaps structure:
struct _GstTypeCaps {
guint16 id; // if of the major type
GData *properties;
}
4. example using arrays
-----------------------
mpg123: an mpeg audio decoder.
// a factory for the major type we use
static GstTypeFactory mp3factory = {
"audio/mp3", // major type
".mp3 .mp2 .mp1 .mpga", // extenstions
NULL, // typefind function
};
// capabilities of the sink pad
static GstTypeCapsFactory mpg123_sink_caps[] = {
"audio/mp3",
"layer", GST_TYPE_INT_RANGE (1, 3),
"bitrate", GST_TYPE_INT_RANGE (8, 320),
"framed", GST_TYPE_BOOLEAN (true),
NULL
};
// capabilities of the source pad
static GstTypeCapsFactory mpg123_src_caps[] = {
"audio/raw",
"rate", GST_TYPE_INT_RANGE (8000, 48000),
"channels", GST_TYPE_INT_RANGE (1, 2),
NULL
};
static GstTypeCaps *sinkcaps = NULL, *rawcaps = NULL;
static gst_mpg123_init (GstMpg123 *mpg123)
{
mpg123->sinpad = gst_pad_new ("sink", GST_PAD_SINK);
gst_element_add_pad (GST_ELEMENT (mpg123), mpg123->sinkpad);
gst_pad_set_caps (mpg123->sinkpad, sinkcaps);
...
}
GstPlugin *plugin_init (GModule *module)
{
...
plugin = gst_plugin_new ("mpg123");
gst_plugin_add_type_factory (plugin, mp3factory);
...
sinkcaps = gst_type_register_caps (mpg123_sink_caps, NULL);
rawcaps = gst_type_register_caps (mpg123_src_caps, NULL);
...
}
mpeg2dec: an mpeg video decoder that can do mpeg1 and mpeg2.
static GstTypeFactory mpegfactory = {
"video/mpeg", // major type
".mpg .mpeg", // extenstions
NULL, // typefind function
};
static GstTypeCapsFactory mpeg2dec_sink_caps[] = {
"video/mpeg",
"mpegtype", GST_TYPE_LIST (
GST_TYPE_INT(1),
GST_TYPE_INT(2),
),
NULL
};
static GstTypeCapsFactory mpeg2dec_src_caps[] = {
"video/raw",
"fourcc", GST_TYPE_LIST (
GST_TYPE_INT32 (0x32315659),
GST_TYPE_INT32 (0x32...),
),
"width", GST_TYPE_INT_RANGE (16, 4096),
"height", GST_TYPE_INT_RANGE (16, 4096),
NULL
};
static GstTypeCaps *sinkcaps = NULL, *rawcaps = NULL;
GstPlugin *plugin_init (GModule *module)
{
...
plugin = gst_plugin_new ("mpeg2dec");
...
sinkcaps = gst_type_register_caps (mpeg2dec_sink_caps, NULL);
rawcaps = gst_type_register_caps (mpeg2dec_src_caps, NULL);
...
}
5. capabilty compatibility
--------------------------
Two pads are compatible if:
- The major types are equal
- range of the sink pad contains the range of the src pad
|
