Martin,
Let me be a little bit clearer:

The URL https://www.youtube.com/embed/86TZ_vJByzk?start=1200&end=1230
in Chrome plays just seconds 1200 to 1230 in a large file as desired and
https://www.youtube.com/embed/86TZ_vJByzk?t=1200 starts properly at 1200 seconds.

If I use this URL in FV

[fvplayer src="https://www.youtube.com/embed/86TZ_vJByzk?start=1200&end=1230"caption="Hoot test" ]

it plays the whole video from start to finish. The relevant website is now at jhhootenanny.org/videos/ where this is tested.

One problem is that the WordPress code editor and block editor convert “&” to “&” even though the & is within parentheses. That is a mistake. But even just defining the start
https://www.youtube.com/embed/86TZ_vJByzk?start=1200 or
https://www.youtube.com/embed/86TZ_vJByzk?t=1200 does not adjust the start time.

Is there some way to make this work in FV?

What I am trying to accomplish is to concatenate the URL in an Access database to play one specific song in a large library of nearly 1000 hours of 3-hour concerts. I can simply play the URL in YouTube but would prefer to have it embedded in my page.

Everything above is mp4 video files. I did a lot of experimenting with FV playing mp3 audios and the times did not work there either.

Peter

In 4 days, I still do not have working code. The following works but the lightbox comes up with a tiny video.
[fvplayer src="https://youtu.be/bQJg6gcpPSo" lightbox="true;text;" caption="click on this link" splash="https://i.ytimg.com/vi/bQJg6gcpPSo/hqdefault.jpg"]
see at https://adriennessongs.com/hoot-videos/ click on test.
The option you specify to use in the editor is not available to me. Is this because I am not using the pro version?
I set the size in the editor window as 1280X720, but that effects the video, not the lightbox. I need the video to come up in the lightbox at 1280X720 size.
Can I set the lightbox size in this code?
Please sends me the code that works.

I am still waiting for an answer. The anchor-text-with-lightbox creates a window in which the video is only about one inch wide. How do you increase the default size. In Settings, FV Player, I have default video size set to 80% height and 80% width. I tried adding size to the URL. But that does not work.

While FV Player appears to be a very good video player, I find the documentation less than minimal and am frustrated that in two days, I have yet to find out how to make this work with lightbox. Do I need to create a whole new page containing the basic short code. I need to do this for 65 videos, so I am looking for an efficient solution.