Question / Help Huge output size?

[ItsaMeC3]

3 weeks ago I recorded a 90 minute long video and it came out at 4.07gb, which is fine.
Yesterday, however, I tried to record another video - same settings, same length... But it came out at 43gb. Now I can't record anything without it having a ridiculous file size. A 05:32 video now has a size of 4.33gb. As far as I know my settings haven't changed.

I'm trying to record in 1080 for YouTube, if anyone can advise of a solution to this problem of mine.
TIA.
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Running OBS 21.1.0 64bit
PC Specs:
CPU: AMD FX-8350
GPU: Asus GeForce GTX 1050Ti
Ram: 16gb ddr3
MoBo: Gigabyte GA-78LMT-USB3
OS: Windows 10 Home
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OBS Settings:
Output->Recording
Output mode: Advanced
Type: Standard
Format: mp4
Audio Tracks: 1
Encoder: x264

Rate Control: CRF
CRF: 15
Keyframe Interval: 0
CPU Usage Preset: ultrafast
Profile: Main

 

[DEDRICK]

CRF: 15

That is essentially lossless

The way CRF works is it allocates as many bits as it needs to maintain a set image quality. 23 is the default, as you go lower the larger the file gets, I wouldn't go lower than 20

Still scenes will use very little bitrate, a scene with a ton of movement will require a substantial amount of bitrate, so there is no constant, predictable filesize. Depending on what you were recording before it is entirely possible your settings haven't changed but your source has.

 

[ItsaMeC3]

CRF: 15

That is essentially lossless

The way CRF works is it allocates as many bits as it needs to maintain a set image quality. 23 is the default, as you go lower the larger the file gets, I wouldn't go lower than 20

Still scenes will use very little bitrate, a scene with a ton of movement will require a substantial amount of bitrate, so there is no constant, predictable filesize. Depending on what you were recording before it is entirely possible your settings haven't changed but your source has.

Tthe 90min/4gb recording was of Castle Crashers, the 90min/40gb recording was Rocket League. I'll try raising the CRF and see if it helps. Thanks for the advice!

 

[Harold]

Low motion recordings will have lower filesizes when using one of the quality based bitrate selections.

And you absolutely should NEVER be saving directly to mp4.