I don't know either. I thought that maybe there are some additional codecs installed along with the program that can somehow influence the preview performance. I'm just trying to find a solution at all costs because it is so frustrating especially knowing that it worked fine, but now the preview with XAVC is sluggish as hell.

It would be great if there was someone willing to suggest some possible solutions.

With me 4K 50p XAVC-S files play in my previeuw screen in preview/best in full framerate without problems on my laptop from signature. Look

To help you maybe you can provide also such a screenshot or otherwise the MediaInfo plus the Vegas properties of your sourcefiles, the preview settings of your files and the location of your sourcefiles.

I installed every single driver, K-little codeck pack,

That is the most worst thing you could do. Those codecs have maybe overwritten your installed Vegas files.

With me 4K 50p XAVC-S files play in my previeuw screen in preview/best in full framerate without problems on my laptop from signature. Look

I know :) It worked for me as well (completely smooth even with full preview screen) until I reinstalled the Windows, and the Sony Movie software. It has to do something with the file format, because when I use the AVCHD then the preview works great. I tried recording two exactly the same videos with Sony a6400. The first in XAVC S ans thge second one in AVCHD. Only the first one causes sluggish preview.

Here are some of the settings.

That is the most worst thing you could do. Those codecs have maybe overwritten your installed Vegas files.

Thank you for the advice. I've already uninstalled the codecs, and reinstalled Sony Movie Studio.

Sorry, but I answered you because your title of the question was about VMS Pl 16.
The screenshots are from the old Sony VMS PL 12, I have not installed anymore.
If you give the same screenshots of VMS Pl 16 maybe I can help you.

@PaulD It's not Sony Movie Studio any more. It's Vegas Movie Studio which has been owned by Magix for a few years now.

As j-v mentions we need VMS16 screenshots in particular Media Properties to see which plug In is being used by VMS16 with XAVCS.

DVDA shouldn't have any effect but the version you get with VMS16 is much better as it's the Pro DVDA7. Magix dropped the Studio version.

Hello again,

Here are the screenshots from the VMS16:

 so4compoundplug.dll plug in is being used with the XAVCS.

What I've managed to determine so far is that the problem is caused most likely by Vegas software settings, because the XAVC S files can be previewed without any problems in the Windows Movie Maker.

Hardware is ok for sure. I used the same computer before and it worked fine with MOvie Studio software, so there has to be a way to solve it.

If you look at the ''Preview Device'' tab you can see that there is Windows Graphics Card selected. I have an external AMD graphic card, and it is not possible to choose it from the drop down list. Apart from the Windows Graphic Card option there is also available: OHCI Compliant IEEE 1394/DV and that's all. However the AMD card is visible under the ''Video'' tab for the GPU acceleration.

It is not only the preview that doesn;t work as it should, but there is also something wrong with rendering the XAVCS files. It takes forever to render just 30 sec of the clip. Before I reinstaled the software I had been able to render 30 min of the footage in XAVCS format as fast as now 1 min clip. It is 30 times slower.

Any help would be very appreciated guys.

Pls see section 6 and the linked post in it.

And also set in the Options/Preferences/ Video the amount of Dynamic RAM preview max on the default 200 or 0.

Thank you so much for the advices guys I really appreciate that, but I've tried them all already. Someone on YouTube recommended to disable the so4 plug-in. Yesterday I tried to set it to FALSE in the Internal tab,but it didn't help. The same applies to the dynamic RAM preview. I tried 0, 200, 2000. 4000 values and nothing worked. What I noticed however is that when I uncheck the ''Scale output to fit display'' in the Preview Device tab, then the preview performance improves a little bit, but it is still far from what I remember when I was working with this software a few months ago.

Have you tried resetting yet? Often worth a try at least "if it worked before". "Reinstalling keeps pretty much all the old settings" though I gather you may not have reinstalled v.16 yet.

If you end up reinstalling Vegas, I would restore a previous system image first. Then video drivers.

The registry junk left behind by K-lite is harder to get rid of than a case of bedbugs.

After 10 hours I'm finally done. Everything works as it should again. I purchased a brand new SSD drive and installed a fresh Windws 7 on it, then I upgraded to Windows 10, installed all necessary drivers. After that the preview works flawlessly.

Thank you again for your help guys, but it looks like either I must have messed up something when I was reinstalling the operating system a few days ago or my old SSD is damaged.