Can someone please help me understand what I did with my video files?

Hi, I record video lessons for my website.

The first video lessons were made with QT screen capture with a little video of me in the corner. They were huge .mov files, but somehow I managed to shrink them.

For example, the first was a 13GB .mov file, but the version of it I uploaded onto my website is a 119MB 55-minute .mp4 video at 720 resolution.

I remember I had issues with the audio not being in sync after exporting it from iMovie.

I also remember using some app with a sheep (possibly?) that someone suggested here where I could select... something. Compression rate... I don't remember.

Now I just finished recording a second batch of videos. This time I took the video and audio of me with my phone, and the screen capture with Quicktime. When I export the video from iMovie the audio is synced, but I ended up with a 1.25GB 15-minute .mp4 video at 720 rez.

I was hoping I could upload 1080p videos given the quality of most videos nowadays, but they are just huge. On my website, I can only upload zip files of up to 1000MB.

Now I resaved a video at low quality 720 and it's still 637MB for 19 minutes. Plus the text on the PDF is fuzzy.

How was I able to get a 55-min .mp4 video at 119MB?

Thanks,

Sergio