Search for releases that specify "HEVC" and "AAC 2.0" and avoid anything labeled "BRRip" (which implies higher bitrate source but often isn't).
300 MB MKV movies are almost exclusively from online communities, often labeled with terms like: 300 Mb Mkv Movies
The 300 MB MKV movie offers several benefits to film enthusiasts: Search for releases that specify "HEVC" and "AAC 2
Avoid 1080p files at 300 MB. They are mathematically impossible to look good due to the pixel density. 480p (DVD quality) is the sweet spot for this file size. specialized encoding tools are required:
If you want to compress your own movies to this size, specialized encoding tools are required: