Yes capture of HDMI screen output is supported on 814x as well. There is no usecase on 814x that demonstrates this but you can refer
/dvr_rdk/mcfw/src_linux/mcfw_api/usecases/ti816x/multich_hd_sdi_dvr.c
multich_hdsdidvr_set_capture_prm
code under #ifdef MULTICH_HDSDIDVR_SIMULATE_HD_CAPTURE
for example usage