This method works for both Android and PC users (should also work for IOS, but not tested).

Trailers can be downloaded from www.data18.com which is a database of thousands of movies. It also has trailers for most of those movies, all from official websites.

Be aware there are two trailers usually, one "full size" of around 1½ to 2 minutes, and the other of only 20 seconds. Be sure to pick the longer version.

1) If your trailer is over 90 seconds go to https://ezgif.com/cut-video. This site is free. If it is less than 90 seconds, jump to step 4.

2) Select your file and upload it.

3) Give the start and end times that you want included. The maximum length on this site is 90 seconds. Download the cut file.

4) Go to https://turboscribe.ai/dashboard and upload your file, transcribe it and export as an SRT file. This site is free but limits you to 3 transcriptions per day of a maximum of 30 minutes each.

5) The Turboscribe file adds its logo on line 1 if you use their free version. Edit and remove it. Also edit for any errors.

6) Go to https://ezgif.com/video-subtitles

7) Upload your video.

8) Select font, colour, size. You can check how it looks after every change you make, although the default choices seem to be best. (Truc and I prefer yellow for subtitles fonts, but that's a personal choice).

9) Create the subtitles file and save it.

10) Go to the subtitles page that you posted previously or are posting. You will see a button to upload your trailer. Click on that and follow instructions.

Remember, for this website, the size limit is 20 MB maximum and the time limit is 90 seconds. If your file is longer than 90 seconds, it will be truncated. Your file will also be downgraded to 360:200 and a low bitrate. That is due to website needs.