Trouble synchronising script start with the start of a video playback

[jkh13]

I am trying to synchronise LEDs flashing with a video being played using a Raspberry Pi 3B+ and the Python wrappers for libVLC. For example, I want the LED to flash red at exactly 2000ms of video playback and green at 5500ms etc.

I can get the timings in-between the LED flashes accurate enough in Python (to within a few ms) but I cannot seem to synchronise the start of the video playback with the start of the timing for the LEDs. I have already tried a few things

1) Initialise the video player, load the media, sleep in the script a few seconds to let the player start and load the media. Call play() and immediately start the LED timings.
-- The playback is always delayed after play is called for 100+ms it seems causing the LEDs to trigger earlier than wanted

2) Query for State.Playing using player.get_state() in a while True loop and starting the LEDs immediately after detection
-- The state change seems to be delayed by 100+ms despite the getState being called in a busy loop, this causes the LED routine to start late

3) Adding a few seconds of black screen to the start of the video, calling player.get_time() after a second or so and sleeping for the duration until the 'start' of the real part of the video
get_time() doesn't seem to give accurate timings, it appears to only update itself every 300ms or so giving it a large window where it is off the actual video progress.

Are there any alternatives I should be considering here? Any way to get more accurate timing for when to start the LED routine? I preferably want the delay to be less than 30ms so that the difference is mostly imperceptible to the eye..

For reference here is some code I have been trying so far:

[1]

Code: Select all

player = vlc.MediaPlayer() player.toggle_fullscreen() media = vlc.Media('/home/pi/Downloads/test.mp4') player.set_media(media) sleep(5) player.play() startLedRoutine()

[2]

Code: Select all

player = vlc.MediaPlayer() player.toggle_fullscreen() media = vlc.Media('/home/pi/Downloads/test.mp4') player.set_media(media) sleep(5) player.play() while True: if player.get_state() == vlc.State.Playing: break startLedRoutine()

[3]

Code: Select all

player = vlc.MediaPlayer() player.toggle_fullscreen() media = vlc.Media('/home/pi/Downloads/test.mp4') player.set_media(media) sleep(5) player.play() sleep(5) # 10 seconds of black screen has been added to the start of the video sleep(10 - player.get_time() * 1000) # sleep for the remainder of the time before 10s is reached startLedRoutine()