Proxies - Larger File Size

Explanation

If the original asset has already been heavily compressed (e.g. using H.264 High profile), the proxy file size will most likely be larger than the original asset.
The H.264 encoder used to create the proxy file is configured to use a "Baseline" profile to maximize decode compatibility; the trade-off is larger filesize/bitrate to maintain the quality of the original video file. Lower compression must then be used, and the proxy file transcoder may create a larger file than the original to preserve the current quality.

from here:

https://learn.fotoware.com/On-Premises/FotoWeb/Troubleshooting_FotoWeb/Why_is_the_transcoded_video_proxy_file_larger_than_the_original%3F#:~:text=The%20H.,of%20the%20original%20video%20file.

---

... the original files are highly compressed. For example, MP4 or HEVC files. If you make a proxy, the files get bigger and so the data is less compressed. This makes it easier to manipulate in editing software, because the footage doesn't have to be uncompressed every time you play it, so it's less taxing for the computer and more responsive when the editor is working with it.

 

---

from here:

https://www.reddit.com/r/VideoEditing/comments/zltpsu/can_someone_explain_proxies_to_me_like_i_was_an/