Videos on most sites make use of progressive downloading, which means that the video is downloaded to my computer, and easy to trace. There are lots of extensions out there
Easy youtube-dl example on macOS (in the command line Terminal; Windows supported too):
# List variants (resolutions/bitrates)
$ youtube-dl -F https://bitdash-a.akamaihd.net/content/MI201109210084_1/m3u8s/f08e80da-bf1d-4e3d-8899-f0f6155f6efa.m3u8
[generic] f08e80da-bf1d-4e3d-8899-f0f6155f6efa: Requesting header
[generic] f08e80da-bf1d-4e3d-8899-f0f6155f6efa: Downloading m3u8 information
[info] Available formats for f08e80da-bf1d-4e3d-8899-f0f6155f6efa:
format code extension resolution note
audio-English_stereo mp4 audio only [en]
628 mp4 320x180 628k , avc1.42c00d, video only
928 mp4 480x270 928k , avc1.42c00d, video only
1728 mp4 640x360 1728k , avc1.42c00d, video only
2528 mp4 960x540 2528k , avc1.42c00d, video only
4928 mp4 1280x720 4928k , avc1.42c00d, video only
9728 mp4 1920x1080 9728k , avc1.42c00d, video only (best)
# Choose a variant to download, and use its format code below
$ youtube-dl --format 628 https://bitdash-a.akamaihd.net/content/MI201109210084_1/m3u8s/f08e80da-bf1d-4e3d-8899-f0f6155f6efa.m3u8
...
frame= 5257 fps=193 q=-1.0 Lsize= 6746kB time=00:03:30.16 bitrate= 263.0kbits/s speed=7.73x
video:6679kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.998669%
[ffmpeg] Downloaded 6907810 bytes
[download] 100% of 6.59MiB in 00:29
$ open f08e80da-bf1d-4e3d-8899-f0f6155f6efa-f08e80da-bf1d-4e3d-8899-f0f6155f6efa.mp4
Use the browser's Developer Tools > Network to get the m3u8 (HLS manifest) URL when starting a streaming video.