ruby-****@sourc*****
ruby-****@sourc*****
2004年 3月 2日 (火) 18:37:57 JST
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REMOTE_ADDR = 195.207.101.112
REMOTE_HOST =
URL = http://ruby-gnome2.sourceforge.jp/?tut-gst-pads-caps
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= Capabilities of a Pad
Since the pads play a very important role in how the element is viewed by the outside world, a mechanism is implemented to describe the pad by using capabilities.
We will briefly describe what capabilities are, enough for you to get a basic understanding of the concepts.
== What Is a Capability
A capability is attached to a pad in order to describe what type of media the pad can handle.
A capability is named and consists of a MIME type and a set of properties.
Below is a dump of the capabilities of the element mad, as shown by (({gst-inspect})). You can see two pads: sink and src. Both pads have capability information attached to them.
The sink pad (input pad) is called 'sink' and takes data of MIME type 'audio/mp3'. It also has three properties: layer, bitrate and framed.
The source pad (output pad) is called 'src' and outputs data of MIME type 'audio/raw'. It also has four properties: format, depth, rate and channels.
Pads:
SINK template: 'sink'
Availability: Always
Capabilities:
'mad_sink':
MIME type: 'audio/mp3':
SRC template: 'src'
Availability: Always
Capabilities:
'mad_src':
MIME type: 'audio/raw':
format: String: int
endianness: Integer: 1234
width: Integer: 16
depth: Integer: 16
channels: Integer range: 1 - 2
law: Integer: 0
signed: Boolean: TRUE
rate: Integer range: 11025 - 48000
== What Are Properties
Properties are used to describe extra information for capabilities. The properties basically consist of a key (a string) and a value. There are different possible value types that can be used:
* an integer value (Fixnum, Bignum);
* an integer range value (Range);
* a boolean value (TrueClass, FalseClass);
* a list value (Array);
* a float value (Float);
* a float range value (Range);
* a string value (String).
== What Capabilities Are Used for
Capabilities describe in great detail the type of media that is handled by the pads. They are mostly used for:
* Autoplugging: automatically finding plugins for a set of capabilities;
* Compatibility detection: when two pads are linked, GStreamer can verify if the two pads are talking about the same media types.
== Getting the Capabilities of a Pad
A pad can have a chain of capabilities attached to it. You can get the capabilities chain with Gst::Pad#caps or Gst::Pad#each_caps:
pad.each_caps do |caps|
puts "Capability name " + caps.name + ", MIME type " + caps.mime
end