OpenMAX Call Sequences

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本文译自PV OpenCORE官方文档《OpenMAX Call Sequences: OHA2.1 rev.1Feb 25, 2009》。

将codec集成到PV OpenCORE多媒体框架的方法有几种：1）作为压缩多媒体输入输出(MIO)组件，2）作为节点(node)，3）作为OpenMAX组件集成到OpenMAX codecs节点中。许多codecs，特别是包含硬件加速器的codes都执行OpenMAX IL接口，并且将OpenMAX接口当成最简单的集成方法。

OpenCORE与OMX core/component的交互

1）OMX core初始化

PlayerDriver::playerThread()

->OMX_MasterInit()(pv_omxmastercore.cpp)

->_Try_OMX_MasterInit(error,status, data)

->_OMX_MasterInit(data)执行所有的OpenMAX IL Core标准函数

->OMX_Init()

OMX_ComponentNameEnum()

OMX_GetRolesOfComponent()

OMXCore Initialization

2）OMX Componentinstantiation, capabilities and port indices

After the OMX Core isinitialized, the next step is typically to instantiate a specific component andenumerate capabilities and port indices. The PV framework will:

l 利用OMX_GetHandle调用来实例化想要的OMX组件

l 利用OMX_GetParameter调用来获取OMX组件的能力和OMX组件上可用端口的数量

l 遍历可用的端口以查找输入端口的索引

l 遍历可用的端口以查找输出端口的索引

OMXComponent Instantiation through OMX_GetHandle

3）OMX componentinput and output buffer negotiation

Before any data can beexchanged, parameters for input and output buffers need to be negotiated. Toaccomplish this, the PV framework:

l 调用OMX_GetParameter来获取input port buffer参数

l 核实(verify) input buffer参数的有效性

l 调用OMX_SetParameter来设置input buffer参数

l 调用OMX_GetParameter来获取output port buffer参数

l 核实(verify) output buffer参数的有效性

l 调用OMX_SetParameter来设置output buffer参数

OMXComponent Buffer Negotiation

4）OMXTransition Loaded->Idel State

The buffer allocation ishandled as part of the allocation to the Idle state. During this transition, PVFramework:

l 调用OMX_SendCommand向OMX组件发送命令以改变组件状态(Loaded->Idel)

l 调用OMX_UseBuffer或OMX_AllocateBuffer向OMX组件发送命令。The call isused NumInputBuffer times for input port, and NumOutputBuffer for output port.

l 等待组件的EventHandler回调。这个callback通知框架组件的状态转换已经完成。

OMXComponent state transition from OMX_StateLoaded->OMX_StateIdle

5）Transition to“Executing”state and data exchange

The transition toexecuting starts the active processing of data. In this step, PV Framework:

l 调用OMX_SendCommand向OMX组件发送命令以改变组件状态(Idle->Executing)

l 等待EventHandler callback，组件的状态转换已完成

l 调用OMX_EmptyThisBuffer或OMX_FillThisBuffer向音频组件发送input或output buffers。组件利用适当的callback返回buffers。

OMXcomponent state transition from idle to execute and data exchange

6）Pausing

A common use-caseinvolves pausing and resuming. In this case, the PV framework:

l 调用OMX_SendCommand向OMX组件发送命令以改变组件状态(Executing->Pause)

l 等待EventHandler callback，组件的状态转换已完成

向OMX组件发送pause命令后，PV框架立即停止向OMX组件发送inpupt/output buffers。

In order to resume, thePV framework:

l 调用OMX_SendCommand向OMX组件发送命令以改变组件状态(Pause->Executing)

l 等待EventHandler callback，组件的状态转换已完成

当接到callback组件状态转换成Executing后，PV框架可以恢复向组件发送OMXinput/output buffers。

OMXcomponent state transition from execute to pause and back

7）Port flush(if applicable)

The port flush call istypically used with a decoder component during repositioning so that any queueddata is discarded. In this situation, the PV framework:

l 调用OMX_SendCommand向OMX组件发送命令flush所有ports。

l 等待两个来自组件input和output ports的EventHandler callback，组件已完成portsflushing。

当发送flush命令后，PV框架立刻停止向OMX组件发送input/output buffers。当收到第二个callback后，PV框架可以恢复向组件发送input/output buffers。