Quality settings do nothing

[billbeans]

mpv version and platform

Debian 12 bookworm
mpv v0.38.0-757 (compiled it myself using https://github.com/mpv-player/mpv-build)

mpv v0.38.0-757-gf6d931301b Copyright © 2000-2024 mpv/MPlayer/mplayer2 projects
 built on Sep  9 2024 18:42:23
libplacebo version: v7.349.0 (v7.349.0-9-gefb89342)
FFmpeg version: N-116987-g071c499026
FFmpeg library versions:
   libavcodec      61.13.100
   libavdevice     61.2.100
   libavfilter     10.2.102
   libavformat     61.5.101
   libavutil       59.36.100
   libswresample   5.2.100
   libswscale      8.2.100

Description

I can't make heads or tails of the quality settings, they don't seem to work. No matter what I set them to, I get a very poor quality video if the clip is longer than a couple of minutes.

This time, I set the target filesize to 0 (what does 'filesize' even mean, bitrate in kbps?), and the CRF to 50 with Two Pass OFF in an attempt to encode a video, much like I would do in Handbrake. But the video comes out looking like shit. So I set CRF to 25 and the file size was the exact same and the video looked the exact same (shit). This clearly shouldn't happen, there's a difference between CRF 50 and CRF 25, no matter the format.

Log file

Here is a log of me opening mpv and doing the same thing, only this time I used CRF 10. It didn't matter, the video came out exactly the same as when I used the other values mentioned above. It was a 3 hour raw gameplay video @ 4K 60fps, and I needed about 2 mins of footage:

Output Format = WebM
Two Pass = no
Apply Current Video Filters = no
Scale Height = 720
Strict Filesize Constraint = no
Write Filename on Metadata = no
Target Filesize = 0 (constant quality)
CRF = 10
FPS = source
Force Square Pixels = no

log.txt