Python script to relatively adjust the volume of a roku TV, can be used in combination with http://devtools.web.roku.com/RokuRemote/

roku_vol.py

import os, sys

# You can hardcode the IP here if it does not change much
ip = "192.168.1.111"

args = sys.argv
del args[0]

if len(args) == 0:
    print("Needs one or two arguments, eg:")
    print("\tpython3 roku_vol.py {relative_volume}")
    print("\tpython3 roku_vol.py {relative_volume} {ip_address}")
    exit()

if len(args) == 1:
    args.append(ip)

amount, ip = args
amount = int(amount)

if amount < -20 or amount > 20:
    print("relative_volume must be between -20 and 20 (run the script multiple times for other ranges)")
    exit()

dir = "Up"
if amount < 0:
    dir = "Down"

# the actual curl command we'll run amount times
cmd = f"""
curl 'http://{ip}:8060/keypress/Volume{dir}' \
-X 'POST' \
-H 'Accept: application/json, text/plain, */*' \
-H 'Origin: http://devtools.web.roku.com' \
-H 'Referer: http://devtools.web.roku.com/' \
-H 'User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.4 Safari/605.1.15'
"""

for x in range(abs(amount)):
    os.system(cmd)