How to ouput MJPEG only when calling Venc_snapshotDump()

Hello,
We're implementing "snapshot" feature with DVR_RDK 4.0 on ti8168 board. When setting MJPEG for primary channels of encoder, the data keeps outputting. However, in order to reduce CPU usage, we hope data outputs only when calling Venc_snapshotDump(). How can we config it in encode chain?

Note. we have tried to set pLinkDynPrm->targetBitRate=0, but got the same result. (Data is always outputted.)

Thank you.

for( i = 0; i < gVencModuleContext.vencConfig.numPrimaryChn; i++ )
{

pLinkChPrm = encPrm.chCreateParams[i];
pLinkDynPrm = &pLinkChPrm->defaultDynamicParams;

pChPrm = &gVencModuleContext.vencConfig.encChannelParams[i];
pDynPrm = &pChPrm->dynamicParam;

pLinkChPrm->format = IVIDEO_MJPEG;
pLinkChPrm->profile = 0;
pLinkChPrm->dataLayout = VCODEC_FIELD_SEPARATED;
pLinkChPrm->fieldMergeEncodeEnable = FALSE;
pLinkChPrm->enableAnalyticinfo = 0;
pLinkChPrm->enableWaterMarking = 0;
pLinkChPrm->maxBitRate = 0;
pLinkChPrm->encodingPreset = 0;
pLinkChPrm->rateControlPreset = 0;
pLinkChPrm->enableSVCExtensionFlag = 0;
pLinkChPrm->numTemporalLayer = 0;

pLinkDynPrm->intraFrameInterval = 0;
pLinkDynPrm->targetBitRate = 100*1000;  // 0
pLinkDynPrm->interFrameInterval = 0;
pLinkDynPrm->mvAccuracy = 0;
pLinkDynPrm->inputFrameRate = pDynPrm->inputFrameRate;
pLinkDynPrm->qpMin = 0;
pLinkDynPrm->qpMax = 0;
pLinkDynPrm->qpInit = -1;
pLinkDynPrm->vbrDuration = 0;
pLinkDynPrm->vbrSensitivity = 0;

}