pvplayer（OpenCores學習–PVPlayer 引擎設計[親測有效]）

OpenCores學習–PVPlayer 引擎設計[親測有效]-

OpenCores學習(3)–PVPlayer 引擎設計[親測有效]PVPlayer引擎是PVPlayerSDK的心臟。它接收和處理所有PVPlayerSDK從用戶和管理PVMF播放多媒體所需的組成及相關業務的請求。其任務應用和簡化高級控制。這個PVPlayer引擎也偵測,處理,和過濾事件和信息生成多媒體播放操作控制。3

PVPlayer引擎是PVPlayer SDK的心臟。它接收和處理所有PVPlayer SDK從用戶和管理PVMF播放多媒體所需的組成及相關業務的請求。其任務應用和簡化高級控制。這個PVPlayer引擎也偵測,處理,和過濾事件和信息生成多媒體播放操 作控制。

3.1 PVPlayerInterface API

PVPlayer用戶界面PVPlayer引擎通過PVPlayerInterface接口類來確定是否有一種適配接口用 戶和PVPlayer引擎。PVPlayerInterface是一種OSCL-based接口和遵循公共接口,除了多媒體播放特定api,PVPlayerInterface提供方法檢索SDK信息、操縱和取消的命令。并描述PVPlayerInterface API,指的是一種PVPlayerInterface API文檔生成的支持的標記。

3.2異步操作

The PVPlayer engine processes most commands initiated by API calls asynchronously. There are some commands that are processed synchronously and they can be differentiated by the return value. Synchronous commands return a PVMF status code which tells the user whether the command succeeded or not and if it did fail, what the error was. All asynchronous commands return a command ID. For the user to be notified of asynchronous command completion, the user must specify a callback handler when instantiating PVPlayer engine via the factory function. When the asynchronous command completes, PVPlayer engine calls the callback handler with the command ID for the command, command status, and any other relevant data. To process the command asynchronously, the PVPlayer engine is implemented as an active object, which gets to run according to the active scheduler running in the thread. The PVPlayer engine expects scheduler to be available when instantiated and the engine itself will not directly create a thread or scheduler.

With asynchronous commands, there is a possibility of commands not completing in expected time. To deal with this issue, PVPlayer engine provides standard PV SDK APIs to cancel a specific or all issued commands. The user of PVPlayer SDK can use these APIs to cancel any request that did not complete in time or are not needed due to changing circumstances. In PVPlayer engine, it might have to deal with lower level components that behave asynchronously. To prevent an unresponsive lower level component from blocking PVPlayer engine operation, PVPlayer engine has timeout handling for any asynchronous commands that it issues. When timeout does occur, the asynchronous command is canceled and is handled appropriately (e.g. command failure, error event).

3.3事件處理

The PVPlayer engine notifies the user of errors and other information not related to API calls as unsolicited events. The notification is handled by making a callback on handlers specified by the user of PVPlayer engine. There are two callback handlers, one for error events and one for informational events, that must be specified by the user when instantiating PVPlayer engine via the factory function.

3.4引擎框架

下面的圖表說明了應用程序使用PVPlayer引擎的接口PVPlayerInterface時直接適配。PVPlayerFactory處理實例化組件和destory的PVPlayerEngine對象。所有PVPlayer引擎的api提供PVPlayerInterface。PVPlayerEngine采用三種回收處理過的應用,PVCommandStatusObserver,PVInformationalObserver,PVErrorEventObserver,通知申請上述指令完成同步誤差和信息的事件。

引擎設計” alt=”OpenCores學習(3)–PVPlayer?引擎設計”>

圖二類圖

3.5狀態機

引擎設計” alt=”OpenCores學習(3)–PVPlayer?引擎設計”>

圖三狀態機

PVPlayer引擎實例化后狀態為IDLE,在IDLE狀態時,可以調用AddDataSource()來指定需要回放的多媒體 數據,然后調用init()初始化數據并且狀態轉為INITIALIZED,在進入INITIALIZED

狀態的時候,用戶可以獲取媒體的tracks和metadata,并且可以調用AddDataSink()去指定具體的data sinks去回放.

在所有的data sinks添加后,用戶調用Prepare(),使引擎建立相關的PVMF節點,并為數據流指定多媒體播放的數據源 和數據接收器,建立需要播放的數據流隊列.用戶在PREPARED狀態時調用Start()進入到STARTED狀態,啟動多媒體播放.在調用Stop()后回到INITIALIZED狀態并且刷新多媒體數據流.

在STARTED狀態時,用戶也可以調用Pause(). Stop().調用Stop()后停止回放,刷新所有數據流,并且使引擎回到初始化狀態.調用Pause(),會停止回放,但不會刷新數據流,而且可以調用Resume()繼續從暫停的地方播放.在PAUSED狀態時可以調用Stop()使引擎回到初始化狀態.

調用Stop()回到INITIALIZED狀態后,數據隊列可以通過調用AddDataSink()和RemoveDataSink()來添加和刪除.在調用Prepare()\Start()重新回放,但是關閉回到IDLE狀態時,或需要重新打開另一個媒體文件時,需要調用Reset().因為在IDLE狀態調用RemoveDataSink()不能刪除所有數據隊列.調用Reset()后,又回到起始狀態,流程如上一樣.如果用戶想退出PVPlayer,也可以調用Reset(),在PREPARED, STARTED,PAUSED狀態時都可以調用該函數.

如果PVPlayer引擎收到錯誤信息或從其它組件傳來 錯誤事件后,引擎會發送ERROR狀態并且嘗試恢復.如果這個錯誤是不可恢復的,剛引擎會清空所有狀態和數據列回到IDLE狀態.此時用戶應該等待PVMFInfoErrorHandlingComplete informational event.

以上是這個狀態機的簡要 描述,具體參考OPENCORE源碼.