You have to modify the demo code to dump 8 channels. I don't know which demo code you have taken for your usecase. If it is taken from
/dvr_rdk/demos/mcfw_api_demos/mcfw_demo/demo_vcap_venc_vdis.c
you should modify
/dvr_rdk/demos/mcfw_api_demos/mcfw_demo/demo_vcap_venc_vdis_bits_wr.c
void *VcapVenc_bitsWriteMain(void *pPrm)
Change below code according to the channels you want to dump
if(pBuf->chnId== gVcapVenc_ctrl.fileWriteChn && fileWriteState == FILE_WRITE_RUNNING)