AOM AV1 and SVT-AV1 Encoders Force 4:2:0 Chroma Subsampling (I420)

Operating System Info

Windows 10

Other OS

No response

OBS Studio Version

30.1.1

OBS Studio Version (Other)

No response

OBS Studio Log URL

https://obsproject.com/logs/ygEQcKH0QiDfJy5p

OBS Studio Crash Log URL

No response

Expected Behavior

Setting the Color Format in OBS to I444 and recording using AOM AV1 or SVT-AV1 should produce a video file with 4:4:4 Chroma Subsampling.

Current Behavior

The output video file has 4:2:0 Chroma Subsampling.
Example video: https://winteris.moe/share/2024-04-01_00-30-33.mkv
MediaInfo output of Example video:

General
Unique ID                                : 67236476256232977644775950872213691578 (0x329546385FB1E5387F1F6985A5A39CBA)
Complete name                            : D:\Dev Showcases\2024-04-01 00-30-18.mkv
Format                                   : Matroska
Format version                           : Version 4
File size                                : 313 KiB
Duration                                 : 5 s 909 ms
Overall bit rate                         : 434 kb/s
Frame rate                               : 60.000 FPS
Writing application                      : Lavf60.16.100
Writing library                          : Lavf60.16.100
ErrorDetectionType                       : Per level 1

Video
ID                                       : 1
Format                                   : AV1
Format/Info                              : AOMedia Video 1
Format profile                           : Main@L5.0
Codec ID                                 : V_AV1
Duration                                 : 5 s 900 ms
Width                                    : 2 304 pixels
Height                                   : 1 296 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 60.000 FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Default                                  : No
Forced                                   : No
Color range                              : Full
Color primaries                          : BT.709
Transfer characteristics                 : BT.709
Matrix coefficients                      : BT.709

Audio
ID                                       : 2
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : A_AAC-2
Duration                                 : 5 s 909 ms
Channel(s)                               : 2 channels
Channel layout                           : L R
Sampling rate                            : 48.0 kHz
Frame rate                               : 46.875 FPS (1024 SPF)
Compression mode                         : Lossy
Title                                    : Track1
Default                                  : No
Forced                                   : No

Steps to Reproduce

1. Set Advanced > Video > Color Format to I444 (8-bit, 4:4:4, 3 planes)
2. Change Output > Output Mode to Advanced
3. Set Output > Recording > Video Encoder to AOM AV1 or SVT-AV1
4. Press Start Recording
5. Observe the output video file has 4:2:0 Chroma Subsampling upon Stopping Recording

Anything else we should know?

I think the relevant code is here, but I'm not massively familiar with OBS's codebase:
https://github.com/obsproject/obs-studio/blob/3a1035576eb6a7c60c1757b3498d97da5d7bfb3b/plugins/obs-ffmpeg/obs-ffmpeg-av1.c#L53-L65

Also, setting -profile high or -pix_fmt yuv444p has no effect. While AV1's Main Profile doesn't support 4:4:4, its High and Professional Profiles do:

Is this just a relic of the AV1 ecosystem not really supporting High/Professional Profiles until relatively recently?

Start with plugins/obs-ffmpeg/obs-ffmpeg-av1.c at the referenced lines, then reproduce the recording with I444 and AOM AV1 or SVT-AV1 using the listed OBS settings. Compare the resulting file's chroma subsampling with the expected 4:4:4 output and determine whether the encoder profile and pixel format are being passed correctly.