MediaMessage (gb.media)
This class represents a GStreamer message received on a 
MediaPipeline bus.
You get them by handling the MediaPipeline 
Event event.
A message has a type, a name, and a collection of key / value pairs.
Constants
| AsyncDone | Constant for a message posted by control when they complete an asynchronous state change. | 
| AsyncStart | Constant for a message posted by control when they start an asynchronous state change. | 
| Buffering | Constant for a buffering message type. | 
| ClockLost | Constant for a clock lost message type. | 
| DurationChanged | Constant for a duration changed message type. | 
| Element | Constant for an element-specific message. | 
| Eos | Constant for end of stream message type. | 
| Error | Constant for an error message type. | 
| Info | Constant for an information message type. | 
| Latency | Constant for a latency message type. | 
| NewClock | Constant for a new clock message type. | 
| Progress | Constant for a progress message type. | 
| Qos | Constant for a quality of service message type. | 
| RequestState | Constant for a request state message type. | 
| SegmentDone | Constant for a segment done message type. | 
| Start | Constant for a stream start message type. | 
| StateAsync | A synonymous for the AsyncDone constant. | 
| StateChanged | Constant for a state changed message. | 
| Status | A synonymous for the StreamStatus constant. | 
| StepDone | Constant for a step done message type. | 
| StepStart | Constant for a step start message type. | 
| StreamStart | Constant for a message indicating the start of a new stream. | 
| StreamStatus | Constant for a stream status message type. | 
| Tag | Constant for a tag message type. | 
| Toc | Constant for a table of contents message type. | 
| Warning | Constant for a warning message type. | 
Properties
| Count | Return the number of key / values pair stored in the message. | 
| Key | Return the key of last enumerated value stored in the message. | 
| Keys | Return an array of the keys of all values stored in the message. | 
| Name | Return the name of the message. | 
| Type | Return the type of the event as a MediaMessage constant. |