Below is the background story...
Initially, I assumed that the embed code would simply be copied into the HTML file for the slide verbatim, so I tried various options for the YouTube URL as explained in <
https://developers.google.com/youtube/player_parameters>. After some testing, I've realized that the 'autoplay' option is indeed honored. So as soon as the slide that contains a video is shown during online presentation, then the YouTube video in it starts to play automatically on the receiving end as well as on my side. So far, so good.
However, I've also realized that the 'start' and 'end' options are ignored. Even though the 'end' option is not supported, there's a manual workaround: after showing the audience as much as I want them to see, I can move on to the next slide, which terminates the video playing. Still, without the support for the 'start' option, I cannot start playing the video from where I want them to start seeing it.
Then the surprise---I was stunned to learn that the presenter can pause and resume video playing, and it is properly reflected on the audience's side. This made me believe that my initial assumption that the embed code would simply be inserted into the slide for HTML was wrong and some sophisticated processing is done on the embed code. Perhaps options are parsed and event listeners are attached to the video player on the presenter's side (via Iframe Player API <
https://developers.google.com/youtube/iframe_api_reference>?) so pausing and resuming can be properly duplicated on the audience's side.