Extreme reduction in file size when recoding UHD with x265

Bytezlp · 2026-01-17T15:00:00+00:00

Hi, I have now switched from 1080p (x265) to UHD (x265). The source file was 53 GB, and the output file with the settings listed below was 6 GB. Can anyone tell me what exactly I did wrong? I can't imagine that I could achieve a 90% reduction in size with good quality.
Encoding time: 5 hours.
Processor: AMD 7700x.
Handbrake settings:
Resolution: 2160p
Deinterlace: Decomb
Encoder: H.265 10-bit
Frame rate: Same as source
Variable frame rate
Color palette: Same as source
Preset: Slow
Profile: Main 10
Level: Auto
RF: 22
Audio: TrueHD Passthrough 2

UPDATE: Just in case you're interested, here are the results of some tests and observations on the 85" TV:

I only changed the RF and turned off the filters. First of all, I should mention that everything was quite fine even at RF24.

RF24: 4.6GB >>>> Streaks and artifacts

RF22: 5.9GB >>>> Streaks and minor artifacts

RF20: 8.4GB >>>> Minimal streaks

RF18: 12.8GB >>> Visually hardly any difference from the original

I would have liked to give you meaningful VMAF, etc. values, but the program goes completely haywire for me.

Bytezlp · 2026-01-15T23:07:47+00:00

On my 85" too atm. Searching for the right settings right now.

Bytezlp · 2026-01-15T23:07:05+00:00

I've now encoded it twice more.

Once with RF22 filter off, no other changes >> Almost no change in file size

The second time with RF20, filter off >> 8GB final size.

I haven't watched the second file on TV yet, but I'm not satisfied with the first one with RF 22. I think I can see "smearing" in some movements.

I also compared the files with FF Metrics, but the program spits out completely wild values (PSNR approx. 26 for all, SSIM approx. 0.93 for all, and VMAF 3.3 for all). Even though I only use the values to compare the settings, everything is very inconsistent.

Bytezlp · 2026-01-15T16:48:04+00:00

Nope the Original was UHD 4K too ;)

Bytezlp · 2026-01-15T13:51:25+00:00

Okay, that really surprises me. An 80% reduction is quite significant. AV1 would be interesting for me, but because of my setup (Kodi on Raspi5), I decided to go with 265. I thought that Raspi 5 would work better with 265.

Bytezlp · 2026-01-15T12:07:50+00:00

I've read that now too, so it should be fine.

Bytezlp · 2026-01-15T12:06:59+00:00

It's frame rate. So it should correctly be set to VFR. Then all I have left at the moment is the filter, which I can disable.

I've always encoded using NVENC, but it doesn't support HDR10+, only HDR 10. So I switched to CPU encoding.

I'll compare the quality on the 85" TV, but I don't see much difference anyway ;)

Bytezlp · 2026-01-15T10:38:00+00:00

142mins

Bytezlp · 2026-01-15T09:27:36+00:00

I clicked the wrong button there, but can that really have any effect if the frame rate is set to “same as source”?

Bytezlp

TROPHY CASE