different sound volume and watching a movie in the middle of a webinar

Please kindly let me know…

We held a webinar today, and received a few comments from the audience.

1. Sound volume of an uploaded movie:

When we played a movie (uploaded on GTW), the sound volume was OK on PC, but the sound was extremely small on iPhone.
Why does the sound volume change depends on the device?

Is there any way to deal with this problem from the organizer’s side? Or is it a system issue?

2. Watching a movie in the middle of a webinar:

If someone join the webinar in the middle of a session, and a movie was playing…

If on PC, you can watch from the middle of the movie, where it’s playing in real time;

However, if on iPhone n(or other smart phones), the movie starts from the beginning, even though it’s already a half way through in real time.

Therefore, when we move on to Q&A session after the movie, the movie stops in the middle for those who are watching on iPhone,

If you need more explanation or clarification, please call me anytime.

These problems are critical as I organize webinars.