1. 为什么gstreamer是graph-based?

2. Pipelines can be visualised by dumping them to a .dot file and creating a PNG image from that

    如何倒？

3. container和codec的区别？

   container formats: asf, avi, 3gp/mp4/mov, flv, mpeg-ps/ts, mkv/webm, mxf, ogg

4. event->structure作用是什么？

5. GstStructure的作用？

   GstStructure实质是GArray.

   是Key/Value键值对的集合（Collection）

   一般GstCaps, GstEvent, GstQuery, GstMessage会用到GstStructure.

6. GstEvent仅仅提供了几个event，并没有生命周期，谁用它呢？

    GstPad? GstElement? GstPipeline?

    The event class provides factory methods to construct events for sending and functions to query (parse) received events.