If your i9 has an iGPU try to enable it for decoding.

That said, some transitions are just too computationally intensive to preview smoothly in VEGAS today. Create a selection and hit shift + b to create a ram preview.

General
Complete name                            : D:\P1003842.MP4
Format                                   : MPEG-4
Format profile                           : Base Media / Version 2
Codec ID                                 : mp42 (mp42/hvc1)
File size                                : 2.70 GiB
Duration                                 : 4 min 0 s
Overall bit rate                         : 96.2 Mb/s
Frame rate                               : 50.000 FPS
Encoded date                             : 2023-04-12 17:55:44 UTC
Tagged date                              : 2023-04-12 17:55:44 UTC

Video
ID                                       : 1
Format                                   : HEVC
Format/Info                              : High Efficiency Video Coding
Format profile                           : Main 10@L5.1@High
Codec ID                                 : hvc1
Codec ID/Info                            : High Efficiency Video Coding
Duration                                 : 4 min 0 s
Bit rate                                 : 95.9 Mb/s
Width                                    : 3 840 pixels
Height                                   : 2 160 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 50.000 FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 10 bits
Bits/(Pixel*Frame)                       : 0.231
Stream size                              : 2.69 GiB (100%)
Encoded date                             : 2023-04-12 17:55:44 UTC
Tagged date                              : 2023-04-12 17:55:44 UTC
Color range                              : Limited
Color primaries                          : BT.709
Transfer characteristics                 : BT.709
Matrix coefficients                      : BT.709
Codec configuration box                  : hvcC

Audio
ID                                       : 2
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 4 min 0 s
Source duration                          : 4 min 1 s
Bit rate mode                            : Constant
Bit rate                                 : 128 kb/s
Channel(s)                               : 2 channels
Channel layout                           : L R
Sampling rate                            : 48.0 kHz
Frame rate                               : 46.875 FPS (1024 SPF)
Compression mode                         : Lossy
Stream size                              : 3.60 MiB (0%)
Source stream size                       : 3.60 MiB (0%)
Encoded date                             : 2023-04-12 17:55:44 UTC
Tagged date                              : 2023-04-12 17:55:44 UTC

Camera is Panasonic GH5 markII

And your project settings?

I understand that some difficult transitions can be a problem. Frames slow down even on simple crossfades. I was hoping that with such equipment it would be full of comfort. Edius, Premier, Davinci - work perfectly. I love VEGAS, I don't want change.

VEGAS can struggle with 10-bit HEVC + Fx (or multicam, etc.)

Definitely have the iGPU handle decoding in preferences/ file io if you haven't already. Hopefully VEGAS can make better use of GPU resources in the future.

is this the setting you mean? If so, it is enabled. Without this, the preview does not exist. Maybe 10 frames per second. I am surprised that such a powerful program in 2023 can not work in 4K. Proxy is on old hardware and not on new high-end components. Even a $1000 graphics card doesn't do anything. Funny.

In your File I/O HEVC decoding must be checked for your goal

When this option is selected, the preview is a nightmare.

@Lukasz-Pecak Hi, can you click your icon at the top of this page - My Profile & fill in your Signature with the full name of your CPU, GPU & amount of RAM, also inc the Windows & Vegas version, this will then show at the bottom of your comments, thanks 👍

ok :)

@Lukasz-Pecak Thanks, I have to 'shift + b to create a ram preview' as RogerS says for most transitions to get full fps on playback, & some but not all 10bit files can play really badly,

Got to ask, you said 'Even a $1000 graphics card' but I googled your card - if it's the same one it can be bought for £50 & is 10yrs old, Did you make a spelling mistake?

How old is AMD Radeon R9 200 Series?

The Radeon R9 290 and R9 290X were announced on September 25, 2013.

With shift + B it's not a job :(. The card at the moment is R9 200. When I had the RTX 3090 GAMING X TRIO 24GB GDDR6X the problem was exactly the same. So different cards did not give any difference. It was cheaper. In Davinci the difference was huge.
Vegas can't use the potential of the GPU

GeForce RTX 3080 GAMING OC LHR 10GB GDDR6X was the same problem.

Any reason you're shooting HEVC? AVC/h264 edits better. However, for smooth playback of 10 bit video, you may have to make proxies. right click on media in the media pool, "create video proxy", let that process complete, then set your preview quality to "preview". you'll have smooth playback.

is this the setting you mean? If so, it is enabled. Without this, the preview does not exist. Maybe 10 frames per second. I am surprised that such a powerful program in 2023 can not work in 4K. Proxy is on old hardware and not on new high-end components. Even a $1000 graphics card doesn't do anything. Funny.

Yes, that's right for settings. Keep legacy HEVC unchecked.

I have the same settings (also have a 13th gen CPU) and while most media plays fine some 10-bit HEVC is still too challenging for VEGAS. No the graphics card won't help either. You have to make proxy files or shoot a different format.

Really that's what figuring out a workflow is about - what works with the software and hardware you have today. If you insist on this file format and not making proxies I'd suggest a different NLE.

In panasonic GH5 II or Gh6 is the most suitable format today. There is nothing better and more popular. It's not 8K. It's standard 4K. I'm shocked Vegas can't do that. Before writing on the forum, I checked all possible settings. It took me a long time. I thought someone did. From what I can see, Vegas is suitable for the old FullHD. Proxy is good for short recordings. I occasionally do 2.5 hours. Time for a change of beloved Vegas. They are not technologically up to date.

Lukasz, it may not preview that well in HD either- did you test it?

With your powerful CPU you could make VEGAS proxies relatively fast I think, or batch convert it all to a more editing-friendly format before importing it. ProRes is a better option for such recordings (it's 10-bit, 4K, etc.) and VEGAS plays it back perfectly. My understanding is that the GH6 can record in Apple Prores 422 which is a much better editing format.

FullHD is ok. But it's a 15-year-old format. Creating a proxy will give me 2 as much data. I do not need it. I understand if Edius, Premier, Davinci would also run slow. it is not. Vegas lags behind the competition. I have always defended vegas and claimed it was the best editing program. Time for changes. My CPU does what it can. Unfortunately, the limit is Vegas.

The other thing is the constant crashing. Very slow 4K render. Premier does it 2x faster. My love for Vegas is passing. :(

You can delete proxy files when you're done with the project. Sort the media by file type in Windows Explorer.

Each NLE has its strengths and weaknesses. Resolve is very GPU-heavy and doesn't work well on lesser systems. Others pre-cache data to perform better.

HEVC performance isn't great in VEGAS, it's widely known and sure we'd like it to be improved. Are you going to wait around for that or get back to editing?

The other thing is the constant crashing. Very slow 4K render. Premier does it 2x faster. My love for Vegas is passing. :(

Use the NLE that's right for you today. Nobody says you have to use VEGAS if it's not the tool for you.