You an get the live feed straight from the HKJC here:
https://www.youtube.com/channel/UCEZ...Xe3lq7wisO-MHw
Note that the feed doesn't show up until 30 minutes before the first race.
Roku users can fetch the YouTube app and cast the stream directly from the computer or tablet to their TV. Note that it works better if the Roku and computer are both hard-wired (Ethernet) to the router.