Confirming cropping into 4K for 1080 render with no quality loss

RedRob-CandlelightProdctns wrote on 3/24/2023, 6:48 PM

I've always gone with this assumption -- would appreciate if others here would confirm this to be true.

The setup:

A project is set to 1080p
A 4K media event is dropped onto the timeline
That event is pushed in (via Pan/Crop) 30% (image is larger)
Project is set to 'Full Resolution Render', motion blur to "Gaussian', Deinterlace set to 'Blend fields', Resample set to "Disable"

The assumption:

Rendering that project to a 1080p AVC .mp4 file will have zero quality loss from the original source media, since Vegas will be smart enough to know that it's just cropping into the image and not doing any scaling.

Is this accurate?

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Comments

RedRob-CandlelightProdctns wrote on 3/25/2023, 10:26 PM

@RedRob-CandlelightProdctns It's a different workflow if you want voukoder to do the scaling. You feed it your source resolution, so 4K for you, then in voukoder it scales the image. It's in the filter settings

Hmm.. yeah, don't think that would work for me then, since my source is mixed resolutions; I can't just choose 4K and have it represent all the project content.

My typical theatre setup is 6-8 cameras, with my wide and a POV action-cam being 4K to allow for clean pushing into the image as needed ("safety" in the case of wide). My other cams I usually film 1080p, even my 4K cameras, and in-camera enable digital zoom so it pushes into the 4K sensor when needed so the camera op can get tighter. They're already shooting tight and I trust them.

RedRob-CandlelightProdctns wrote on 3/25/2023, 10:27 PM

Try applying the general recommended preset in Voukoder. You can also change the CRF from 23 to 20 or 17 etc for better quality and higher file size.

That's exactly what I did.. the default one (which I presumed was the same as the "general recommended" one -- the "use this if you're not sure which to use" one)

3POINT wrote on 3/25/2023, 11:58 PM

You can also change the CRF from 23 to 20 or 17 etc for better quality and higher file size.

Don't do that when you plan to show your renders on a (U)HDTV. Since Voukoder bitrate is strongly depending on complexity of your Video, lowering the CRF setting can cause peak bitrates which are beyond the max bitrate of your TV, resulting in shocking playback. A common issue for max quality seekers.

My advice use CRF 23 for 1080p and CRF25 for 2160p.

RogerS wrote on 3/26/2023, 12:40 AM

Try applying the general recommended preset in Voukoder. You can also change the CRF from 23 to 20 or 17 etc for better quality and higher file size.

That's exactly what I did.. the default one (which I presumed was the same as the "general recommended" one -- the "use this if you're not sure which to use" one)

I think the real default is not selecting any presets and that's what I assumed you used.

Personally I use renders for uploads to the internet and directly played back from computers hooked to a TV via HDMI or on tablets, so give it high peak bitrates.

3point's warning is a good one as how you intend to use the render also impacts the settings you choose.

RedRob-CandlelightProdctns wrote on 3/26/2023, 12:51 AM

You can also change the CRF from 23 to 20 or 17 etc for better quality and higher file size.

<...snip...> Since Voukoder bitrate is strongly depending on complexity of your Video, lowering the CRF setting can cause peak bitrates which are beyond the max bitrate of your TV, resulting in shocking playback.

What playback method would have this problem.. I mean.. TV's aren't natively playing these video files (unless on a thumb-drive maybe??).. so it'll either be a streaming service (Vimeo, YouTube, whatever) via Chromecast or a directly connected computer, and then those playback devices would deal with ABR, VBR, etc. to get it playable, ya?

RogerS wrote on 3/26/2023, 12:56 AM

Pretty sure he is referring to playing it directly on a thumb drive or NAS.

3POINT wrote on 3/26/2023, 2:35 AM

AFAIK, (U)HDTV have a limitation of 100 Mbps. Voukoder renders can easily peak this when CRF setting is too low. Voukoder CRF has no max bitrate setting, it just tries to maintain the quality of the CRF setting.

john_dennis wrote on 3/26/2023, 3:23 PM

@RedRob-CandlelightProdctns said:

"Also -- gotta admit -- I don't know how to interpret your quality/loss results (or how they are measured)... they look scientific and all, I just don't know what they mean!"

Without knowing what all the measurements mean, here is an example of a perfectly lossless render.

Date: 2023/03/26  11:44:23  
Description: Crop Test Legacy 8 bit UHD to UHD Uncompressed
Frames Processed: 330
Mean Squared Error: 0
Peak Signal to Noise Ratio: 99
Structural Similarity Metric: 1

Compare that to any render to AVC/AAC...

Date: 2023/03/25  09:06:47  
Description: Crop Test Legacy 8 bit UHD to UHD Magix AVC/AAC
Frames Processed: 330
Mean Squared Error: 5.104
Peak Signal to Noise Ratio: 41.137
Structural Similarity Metric: 0.7519

... and you'll start to see what you're losing.

The output file is a very impractical uncompressed avi. Some loss of quality from the original is the price of living in a world with limits.

General
Complete name                            : Crop Test Legacy 8 bit UHD to UHD Uncompressed.avi
Format                                   : AVI
Format/Info                              : Audio Video Interleave
Format profile                           : OpenDML
File size                                : 7.65 GiB
Duration                                 : 11 s 11 ms
Overall bit rate                         : 5 968 Mb/s
Encoded by                               : John Dennis
Copyright                                : 2023
TCOD                                     : 0
TCDO                                     : 110110000

Video
ID                                       : 0
Format                                   : RGB
Codec ID                                 : 0x00000000
Codec ID/Info                            : Basic Windows bitmap format. 1, 4 and 8 bpp versions 
                                                   are palettised. 16, 24 and 32bpp contain raw RGB samples
Duration                                 : 11 s 11 ms
Bit rate                                 : 5 966 Mb/s
Width                                    : 3 840 pixels
Height                                   : 2 160 pixels
Display aspect ratio                     : 16:9
Frame rate                               : 29.970 (30000/1001) FPS
Color space                              : RGB
Bit depth                                : 8 bits
Bits/(Pixel*Frame)                       : 24.000
Stream size                              : 7.65 GiB (100%)

Audio
ID                                       : 1
Format                                   : PCM
Format settings                          : Little / Signed
Codec ID                                 : 1
Duration                                 : 11 s 11 ms
Bit rate mode                            : Constant
Bit rate                                 : 1 536 kb/s
Channel(s)                               : 2 channels
Sampling rate                            : 48.0 kHz
Bit depth                                : 16 bits
Stream size                              : 2.02 MiB (0%)
Alignment                                : Aligned on interleaves
Interleave, duration                     : 245  ms (7.33 video frames)
Interleave, preload duration             : 250  ms