openmax IL 学习

二、Omx架构：

 

二、Omx 使用：

1、initialize.

OMX_Init();

 

2. get componenthandle.

OMX_GetHandle();

For example:

OMX_CALLBACKTYPE videodeccallbacks = {

    .EventHandler =videodecEventHandler,

    .EmptyBufferDone =videodecEmptyBufferDone,

    .FillBufferDone =videodecFillBufferDone

  };

/*getting video decoder handle*/

OMX_GetHandle(&videodechandle, "OMX.vender.video_decoder.h264",NULL, &videodeccallbacks);

/*getting color converter component handle*/

OMX_GetHandle(&colorconv_handle, "OMX.ven.video_colorconv.ffmpeg",NULL, &colorconv_callbacks);

/** getting sink componenthandle  */

OMX_GetHandle(&fbdev_sink_handle,"OMX.ven.fbdev.fbdev_sink", NULL, &fbdev_sink_callbacks);

 

3. set up the tunnelbetween the components.

OMX_SetupTunnel(  OMX_HANDLETYPE hOutput,  OMX_U32 nPortOutput,  OMX_HANDLETYPE hInput,  OMX_U32 nPortInput) ;

 

For example:

OMX_SetupTunnel(videodechandle,1, colorconv_handle, 0);

OMX_SetupTunnel(colorconv_handle,1, fbdev_sink_handle, 0);

 

videodecà Colorconvàfbdev_sink

 

4.control components.

            Thereare two type of communication control:

1)send command.

a.      OMX_CommandStateSet  /**< Change the component state */

b.     OMX_CommandFlush,       /**< Flush the data queue(s) of acomponent */

c.      OMX_CommandPortDisable, /**< Disable a porton a component. */

d.     OMX_CommandPortEnable,  /**< Enable a port on a component. */

 

2)Send data.

a.      OMX_CommandMarkBuffer,  /**< Mark a component/buffer forobservation */

 

5. components stateMachine.

    OMX_StateIdle,        /**< component initializationhas been completed successfully and the component is ready to to start. */

    OMX_StateExecuting,   /**< component has accepted the startcommand and is processing data (if data is available) */

    OMX_StatePause,       /**< component has received pausecommand */

    OMX_StateWaitForResources,/**< component is waiting for resources, either after                       preemption or before itgets the resources requested. See specification for complete details. */

For example:

OMX_SendCommand(videodechandle,OMX_CommandStateSet, OMX_StateExecuting, NULL);

 

6. buffer control.

/*will send a buffer full of datato an input port of a component. The buffer will be emptied by the component andreturned to the application via the EmptyBufferDone call back*/

OMX_EmptyThisBuffer()

/*will send an empty buffer to anoutput port of a component.  The bufferwill be filled by the component and returned to the application via theFillBufferDone call back*/

OMX_FillThisBuffer();

/* will request that thecomponent use a buffer (and allocate its own buffer header) already allocated

    by another component, or by the IL Client*/

OMX_UseBuffer();

/*will request that the componentallocate a new buffer and buffer header.*/

OMX_AllocateBuffer();

/*will release a buffer headerfrom the component which was allocated using either OMX_AllocateBuffer orOMX_UseBuffer.*/

OMX_FreeBuffer();

For example:

 OMX_EmptyThisBuffer(videodechandle,pInBuffer1);

OMX_FillThisBuffer(videodechandle,pOutBuffer1);

 

7. data flow betweendifferent component.

For example:   decoder àcolorConv

/*set pOutBuffer1 to the decodercompoment output buffer*/

OMX_FillThisBuffer(videodechandle,pOutBuffer1);

/*read the compressed data fromfile to pInBuffer1*/

fread(pInBuffer1->pBuffer,1, buffer_in_size, fd);

/*put the pInBuffer1 to thedecoder component input buffer, began to decoder the data*/

OMX_EmptyThisBuffer(videodechandle,pInBuffer1);

/*will trigger this callback whendecoder decode one frame */

videodecFillBufferDone(OMX_OUTOMX_BUFFERHEADERTYPE* pBuffer){

/*we will put the decoded frameto the color converter component input buffer */

pInBufferColorConv1->pBuffer== pBuffer->pBuffer;

pInBufferColorConv1->nFilledLen= pBuffer->nFilledLen;

OMX_EmptyThisBuffer(appPriv->colorconv_handle,pInBufferColorConv1);
}

 

二、编写omx  component：

Component 需从source,filter或者sinkcomponent 派生，然后可以添加特有的属性和方法。

遵循openMax IL 规范，必须重写的函数：

omx_h264dec_component_Constructor();

omx_h264dec_component_SetParameter();

omx_h264dec_component_GetParameter();

必须实现的函数：

omx_videodec_base_component_BufferMgmtCallback();

 

 

组件的功能和其定义的端口类型密切相关，通常情况下：

只有一个输出端口的，为Source组件;

只有一个输入端口的，为Sink组件;

有多个输入端口，一个输出端口的为Mux组件;

有一个输入端口，多个输出端口的为DeMux组件;

输入输出端口各一个组件的为中间处理环节，这是最常见的组件。