GStreamer随笔1 - Element+Pad

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前言

        GStreamer(Gst)最初做为一个多媒体框架在业界闻名，基于插件(plugins)的流水线(Pipeline)管理使得其在多媒体处理中极其灵活。插件化的需求在AI领域也有应用场景，GStreamer在AI领域(Nvidia AI 框架DeepStream)的应用也非常广泛。

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一、GStreamer框架

What is GStreamer?

https://juejin.cn/post/7025435937500823582

1. gstreamer tools：gst-inspect用于查看插件的相关信息，gst-launch用于命令行启动创建一个应用链路，gst-editor没有用过；

2. gstreamer core framework：GStreamer核心框架，体统整个框架的管理，核心模块包括element，event，buffer，bus，pipeline，clock，synchronization等；

类型	发送	接收	应答
message	element	bus
event	Application, element	element
query	application	element	Application
buffer	element	element

3. gstreamer plugins：多种类型的插件，包括协议类，数据源，格式转换，编解码，滤波，数据宿，以及三方插件(AI插件).

二、基础概念

        在使用Gst之前，我们先熟悉几个基础概念，以便更好地了解GStreamer工作原理。

1. Element

Gstreamer- 元素(Elements)_gstreamer 释放element-优快云博客

/**
 * GstElement:
 * @state_lock: Used to serialize execution of gst_element_set_state()
 * @state_cond: Used to signal completion of a state change
 * @state_cookie: Used to detect concurrent execution of
 * gst_element_set_state() and gst_element_get_state()
 * @target_state: the target state of an element as set by the application
 * @current_state: the current state of an element
 * @next_state: the next state of an element, can be #GST_STATE_VOID_PENDING if
 * the element is in the correct state.
 * @pending_state: the final state the element should go to, can be
 * #GST_STATE_VOID_PENDING if the element is in the correct state
 * @last_return: the last return value of an element state change
 * @bus: the bus of the element. This bus is provided to the element by the
 * parent element or the application. A #GstPipeline has a bus of its own.
 * @clock: the clock of the element. This clock is usually provided to the
 * element by the toplevel #GstPipeline.
 * @base_time: the time of the clock right before the element is set to
 * PLAYING. Subtracting @base_time from the current clock time in the PLAYING
 * state will yield the running_tim