Est-ce que c'est correct et compréhensible en anglais?

If the subtitles are not synchronized with your version of movie, do not use first line of subtitles as the first synchronization point, as it is set to appear slightly before the first sentence is actually spoken in movie. Instead, for the purpose of synchronisation, use second, third or any other line from the movie’s beggining.

I need help from native English speaker.

If the subtitles are not synchronized with your version of movie, do not use first line of subtitles as the first synchronization point, as it is set to appear slightly before the first sentence is actually spoken in movie. Instead, for the purpose of synchronisation, use second, third or any other line from the movie’s beggining.

I need help from native English speaker.

* ** If the subtitles are not synchronized with your movie's version, do not use the first subtitles' line as first synchronization's point. This one is set up to appear slightly before the first sentence is expressed in the movie. For synchronisation's purposes, use the second, third or any other line from the movie’s beginning instead. ***

Je ne suis pas english native speaker, mais comme personne ne t'a répondu, je me suis lancée 😉

* ** If the subtitles are not synchronized with your movie's version, do not use the first subtitles' line as first synchronization's point. This one is set up to appear slightly before the first sentence is expressed in the movie. For synchroniZation's purposes, use the second, third or any other line from the movie’s beginning instead. ***

Je ne suis pas english native speaker, mais comme personne ne t'a répondu, je me suis lancée 😉

Merci beaucoup.

I'm neither native English speaker, nor native French speaker. 🙂

Yes, the paragraph is comprehensible. I would add the word "the" in two places (noted in bold) to make the sentence correct.

If the subtitles are not synchronized with your version of movie, do not use the first line of subtitles as the first synchronization point, as it is set to appear slightly before the first sentence is actually spoken in movie. Instead, for the purpose of synchronisation, use the second, third or any other line from the movie’s beggining.

Thanks a lot but I've already "published" my text.

And this was my final version:

If the subtitles are not synchronized with your video, do not use the first subtitles line as first synchronization point, as it is set up to appear slightly before the first sentence is spoken in the movie. For synchronization purposes, use the second, third or any other line from the movie’s beginning instead.