Media API Basics

The QNX Momentics development suite requires version 1.1 of the Media API. (The version released at the QNX 2000 conference (version 1.0) isn't compatible).

The Media API consists of a set of states, commands, and data structures that're needed for a plugin to switch from one state to the other. This information is defined in the MvPluginState structure in the <Mv.h> header file.

Plugin states

The following is a list of valid plugin states. A description of each state is in the MvCommandType Descriptions appendix.

MV_CLOSED
MV_DEAD
MV_NOTREADY
MV_OPENING
MV_PAUSED
MV_PLAYBW
MV_PLAYING
MV_PREFETCHING
MV_SCANBW
MV_SCANFW
MV_SLOW
MV_STEP
MV_STOPPED

Command types

The following list details some of the command types defined in <Mv.h>. All commands are mutually exclusive, that is, you can't make two commands into one. A description of each command is in the MvCommandType Descriptions appendix.

CMD_PLUGIN_ANGLE
CMD_PLUGIN_CLOSE
CMD_PLUGIN_DIRECT_AUDIO
CMD_PLUGIN_DISPLAY_GUI
CMD_PLUGIN_GET_STATUS
CMD_PLUGIN_MENU
CMD_PLUGIN_MUTE
CMD_PLUGIN_OPEN_URLS
CMD_PLUGIN_PAUSE
CMD_PLUGIN_RESERVED_0
CMD_PLUGIN_SCAN_BACK
CMD_PLUGIN_SCAN_FORWARD
CMD_PLUGIN_SEEK_RELATIVE
CMD_PLUGIN_SEEK_TO
CMD_PLUGIN_SELECT
CMD_PLUGIN_SELECT_AUDIO
CMD_PLUGIN_SELECT_DOWN
CMD_PLUGIN_SELECT_LEFT
CMD_PLUGIN_SELECT_RIGHT
CMD_PLUGIN_SELECT_SUBTITLE
CMD_PLUGIN_SELECT_UP
CMD_PLUGIN_SEND_MESSAGE
CMD_PLUGIN_SET_GUI_STATUS
CMD_PLUGIN_SET_PARAMETER
CMD_PLUGIN_SET_WINDOW
CMD_PLUGIN_SLOW_MOTION
CMD_PLUGIN_START
CMD_PLUGIN_STEP
CMD_PLUGIN_STOP
CMD_PLUGIN_USER_0

Switching between plugin states

Generally, the flow of execution for a plugin is for phplay to:

• load the plugin and call MvInit() to initialize
• send commands to play, stop, etc.,
• terminate and unload the plugin.

The following diagram details how states switch between the media player and the plugins:

A generalized Plugin State Transition Diagram.

Note 1

The phplay media player doesn't allow you to do this because play and pause are the same button, but the plugins can handle this.

Note 2

When you want to play a media file, the application must send CMD_PLUGIN_OPEN_URLS to the plugin. If the player doesn't need to change plugins to play the file, it sends CMD_PLUGIN_CLOSE followed by the CMD_PLUGIN_OPEN_URLS command.

Note 3

After a CMD_PLUGIN_OPEN_URLS command has been sent, the player waits for the plugin to change its state to MV_STOPPED, and then it sends CMD_PLUGIN_SEEK_TO with an offset of 0 to reposition the file pointer to the beginning of the file.