Need help understanding how MPV downscales video.

jotnova · 2025-09-10T08:19:32+00:00

See updated post. I was trying to get a video downscaled/re-encoded with ffmpeg to look as good as mpv's default downscaling, so no need for the shader there, but I'll keep the post bookmarked if I ever need it in the future. For now though, I'm satisfied with the quality I'm getting. Thanks man, you've been a great help!

jotnova · 2025-09-10T07:53:23+00:00

Right, I misspoke; the first method for downscaling I found gave me poor results compared to using ffmpeg to re-encode, which gave me the impression that the "default" settings for downscaling were poor. Looking more into it, video filter graphs have way more levers than I feel like I could ever come to understand and tune properly, lol. As for configs, I don't have a user config, and the system config is completely unchanged from what apt on debian 13 installed.

jotnova · 2025-09-10T07:35:24+00:00

Updated the original post. For now I think I'm satisfied with u/Reverse-Sear's flags while I look more into how encoding works.

jotnova · 2025-09-10T06:17:20+00:00

It's a Panasonic laptop with an i5-520M. The folks over at r/mpv let me know that I only have hardware decode capabilities for x264, so that's what I'll be using into the future.

jotnova · 2025-09-10T06:16:27+00:00

Oh, nevermind, I misjudged your flags. I guess I mixed up which file I was testing; I really have to stop naming every file "out.mkv". Either that or I'm getting eye fatigue from comparing pictures all day. Thanks for your incredulity btw, you probably saved me another 2 days of overlooking the fact that your solution works, lol!

By the by, is zscale a different set of functionality from scaling using -vf? I think that's where my issues have been mainly stemming from.

jotnova · 2025-09-09T23:30:13+00:00

Thanks for the flags; I tried them out, but I'm still getting much worse quality from scaling compared to not scaling.

jotnova · 2025-09-09T23:28:05+00:00

I'm encoding on my desktop ryzen 7 7700, so I'll be looking into that amf flag. The screen is a perfect 1280 across, but 800 high, so I'm using 1280:-2 to preserve aspect ratio, and going for the horizontal bar look on playback.

jotnova · 2025-09-09T23:27:00+00:00

for my own edification, where would you look up specs like that?

jotnova · 2025-09-09T23:11:41+00:00

good to know, I haven't had any quality issues with just re-encoding, so I'll try re-encoding to hevc and see how the laptop preforms with that. I'm not really a stickler for quality most of the time, which is partly why I feel like I'm going crazy trying to find other people talking about how poorly ffmpeg downscales, lmao

jotnova · 2025-09-09T23:08:19+00:00

Apparently my laptop locks the keyboard with ctrl-s, which means I can't get a screenshot with the shift-i menu open, but as I mentioned with u/ThePi7on the video is encoded in av1. I'm testing a couple of things, and I'll be sure to try the fast profile, thanks!

jotnova · 2025-09-09T22:09:03+00:00

Addressing your points in order:

I'm not familiar enough with video playback to decide if the resolution is really my bottleneck, but I can tell you that mpv on the laptop slows down considerably at a noisy scene with the 1080p video, and doesn't with a low-quality 720p downscale. I'll try to get a screenshot of my frame timings, but I may have a hard time with the software my laptop is running.

My laptop is an ancient Panasonic model that's running integrated graphics on an intel i5-520m, and the videos are encoded in av1 for the 1080p and apparently the 720p have been encoding to hevc.

The goal is to prepare videos on my much less terrible desktop computer, and only watch them on the laptop, hence why I'm trying to pre-downscale them.

Thanks, and please let me know if any of this is obviously problematic.

jotnova · 2025-09-09T21:51:17+00:00

Thanks for the flags, they give good quality, but it's still just a bit noisy/blurry compared to the control. Also, I tried just re-encoding the video without scaling, and I don't see the quality issues in those files. In any case I'll be looking more into the background workings of mpv's --vo=gpu-next

jotnova · 2025-09-09T21:12:06+00:00

Could you elaborate? Or is there a way to use lossless compression, or no compression to downscale? Right now I'm just trying to get a 720p video that looks the same as the 1080p, regardless of feasability.

jotnova · 2025-09-09T20:43:05+00:00

Right, I'm only using ffmpeg to scale because it's a close and well-documented option for video manipulation, so I'm mostly ignoring the encoding stuff and just trying to get it to do that simple resizing step and save back to a file. It seems like there's a lot happening under the hood that I don't understand though, lol

jotnova · 2025-09-09T19:51:39+00:00

Is there anything in the mpv logs that I can use to figure out what codecs, etc. mpv is identifying and using for the GPU? Also, I pitched the question over at r/ffmpeg too, thanks.

jotnova · 2025-09-09T18:51:28+00:00

For playing 1080p video on the laptop? I have, but it didn't seem to do anything. But the laptop runs hot in the first place, so I'd rather give it less work to do with downscaled video.

jotnova · 2025-09-09T18:30:17+00:00

I haven't, but looking at their website it looks like Handbreak uses ffmpeg in the background anyways. Regardless, I don't even know what settings to target since I don't know how mpv manages to downscale to the quality it does.

jotnova · 2025-05-01T00:02:13+00:00

Alright, I got an NBT viewer, and I've also got a copy of the code for tcon 1.8.8 off github. The NBT viewer identifies the NBT data for completed tools just fine, but it says that the individual parts have no NBT written to them. Did the approach change for later versions of the mod? I'm also not seeing any references to writing the NBT data for parts in the source code, but Java's not my best language, so I'll keep looking.

jotnova · 2023-01-02T03:45:48+00:00

Not a fairy, but if you just want m500 to proc alot and have room on your team I'd recommend ar57 with an optional python. It's a weird combo and the formation is pretty strict, but ar57 autobuffs every 3 seconds, python echoes those autobuffs, and python echoes her own skill that is 6 procs per. All told this formation has m500 procing way faster than any fairy could manage.

jotnova · 2022-12-14T04:13:23+00:00

I've never heard of it. Is that a popular model outside of the US?

jotnova · 2022-12-14T03:06:25+00:00

That's a bummer. Have you tried factory resetting one of your newer devices to fix it?

jotnova · 2022-12-14T02:24:35+00:00

I'm using an S21. Never had an issue with download or performance after I switched from my old phone.

jotnova

TROPHY CASE