Getting error: " javascript error: Cannot read property" when tracking HTML video current Time using the combination of JavaScript and Selenium

Question

I would like in interval to track video play progress in a HTML video.

Based on the tutorial, the HTML video DOM timeupdate event can be achieved by something like below:

from selenium import webdriver
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.common.by import By
from selenium.webdriver.support import expected_conditions as EC
import time

chrome_options = webdriver.ChromeOptions()
browser = webdriver.Chrome(executable_path=r"\Browsers\chromedriver.exe",
                           options=chrome_options)


browser.get("https://www.youtube.com/watch?v=nXbfZL5kttM")

WebDriverWait(browser, 70).until(EC.element_to_be_clickable(
(By.XPATH, "//button[@aria-label='Play']"))).click()

javascript_to_execute = ' return document.getElementById("ytplayer").currentTime();'
for x in range(0, 2):
    time_current = browser.execute_script(javascript_to_execute)
    print(time_current)
    time.sleep(1)

However, I got the following error

Message: javascript error: Cannot read property 'currentTime' of null

May I know where did I do wrong. Appreciate for any hint or help. Thanks in advance

Answer 1

The following code should work thanks to the suggestion made from OP1. To obtain the currentTime of a HTML video using JS, the following can be considered.

The JS code, to extract the video current time is

"return document.getElementsByTagName('video')[0].currentTime;"

The above JS can be executed using the method execute_script

   time_video = browser.execute_script("return document.getElementsByTagName('video')[0].currentTime;")

To investigate whether the above implementation is able to obtain the video timing, say, in the middle of the video. We first jump to a position, say 180 sec from the starting point using the code below.

player_status = browser.execute_script("document.getElementsByTagName('video')[0].currentTime += 180;")

The full code are as below;

from selenium import webdriver
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.common.by import By
from selenium.webdriver.support import expected_conditions as EC
import time

chrome_options = webdriver.ChromeOptions()
browser = webdriver.Chrome(executable_path = r"some_path\Browsers\chromedriver.exe",
                           options = chrome_options)


browser.get("https://www.youtube.com/watch?v=nXbfZL5kttM")

WebDriverWait(browser, 70).until(EC.element_to_be_clickable(
    (By.XPATH, "//button[@aria-label='Play']"))).click()
print('Fast forward')
player_status = browser.execute_script("document.getElementsByTagName('video')[0].currentTime += 80;")
print('Get Current time')
time_video = browser.execute_script("return document.getElementsByTagName('video')[0].currentTime;")