Thank you for the info! I have Vegas Pro version 20.0 (Build 411). Also, I'm on Windows 10 Home version 22H2. I don't know what camera was used to film it, unfortunately. I do know that the original video is 50 frames per second and UHD resolution if that helps.

 I don't know what camera was used to film it, unfortunately.

https://www.vegascreativesoftware.info/us/forum/faq-how-to-post-mediainfo-and-vegas-pro-file-properties--104561/

General
Complete name                            : C:\! Current Projects\Freelance\harrybenmore\original footage\Copy of Alpaca 001.mp4
Format                                   : MPEG-4
Format profile                           : Base Media / Version 2
Codec ID                                 : mp42 (mp42/mp41)
File size                                : 7.15 MiB
Duration                                 : 1 s 820 ms
Overall bit rate mode                    : Variable
Overall bit rate                         : 33.0 Mb/s
Frame rate                               : 50.000 FPS
Encoded date                             : 2023-10-04 09:14:49 UTC
Tagged date                              : 2023-10-04 09:14:50 UTC
TIM                                      : 00:00:00:00
TSC                                      : 50
TSZ                                      : 1

Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High@L5.2
Format settings                          : CABAC / 2 Ref Frames
Format settings, CABAC                   : Yes
Format settings, Reference frames        : 2 frames
Codec ID                                 : avc1
Codec ID/Info                            : Advanced Video Coding
Duration                                 : 1 s 820 ms
Bit rate                                 : 32.4 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                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.078
Stream size                              : 7.02 MiB (98%)
Language                                 : English
Encoded date                             : 2023-10-04 09:14:49 UTC
Tagged date                              : 2023-10-04 09:14:49 UTC
Color range                              : Limited
Color primaries                          : BT.709
Transfer characteristics                 : BT.709
Matrix coefficients                      : BT.709
Codec configuration box                  : avcC

Audio
ID                                       : 2
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 1 s 820 ms
Source duration                          : 1 s 856 ms
Bit rate mode                            : Variable
Bit rate                                 : 314 kb/s
Maximum bit rate                         : 318 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                              : 69.6 KiB (1%)
Source stream size                       : 71.2 KiB (1%)
Language                                 : English
Encoded date                             : 2023-10-04 09:14:50 UTC
Tagged date                              : 2023-10-04 09:14:50 UTC

Nothing remarkable about your video source.

Might try enabling Legacy AVC Decoding ( Options->Preferences->File I/O ) to see if that helps.

Hmm, I didn't even know about that File I/0 tab. I just tried your advice, and every other combination of settings on that tab, but nothing changed. :-( I set it back how it was for now.

You could add the word [BUG] to your topic title, to make sure it gets noticed by developers.

Hopefully the bug will be fixed.

What about editing the 50p footage on a 25p timeline for 2x slow motion?

You could add the word [BUG] to your topic title, to make sure it gets noticed by developers.

Good idea. I'll do that. Thanks!

What about editing the 50p footage on a 25p timeline for 2x slow motion?

Good thinking! That did work for this particular instance. I would love to hear if anyone may have a solution for the GPU acceleration bug for when I need to work with a lower framerate clip. I'll submit an official support request and keep you guys posted in case anyone else runs into this problem. Thanks!

How did you do the slow motion exactly?

One other idea is to use a velocity envelope, slow your footage to some amount and then in project properties (edit: or just on the event using an "event switch") have resample set to "optical flow." If that works without artifacts it could be a workaround for when you have to slow down clips already at the project framerate.

I CONFIRM!

With any active GPU in the video tab, the image is bitten at the edges and breaks up when moving left or right.
If you turn off the GPU, it's great.

How to duplicate the error.
- Select a video that moves sideways.
- activate Optical flow in the properties tab
- slow it down to 10% for example
- Switch the video preview to Good or Best Full
- watch how it breaks down differently at the edges when the GPU is active
- turn off the GPU and enjoy the change

GPU ON

GPU OFF

TWIXTOR

Slowmotion needs an overhaul. The Twixtor plugin is still the best.

I pointed this out earlier. Unfortunately, almost everyone here ignores my various error warnings. Maybe you'll have better luck.

@pierre-k Twixtor is often good but not here, can't accurately differentiate the soccer player from the grass, would you be able to upload the original footage at 1x here, you may have a good quality assessment benchmark for optical slowmotion.

@pierre-k Twixtor is often good but not here, can't accurately differentiate the soccer player from the grass, would you be able to upload the original footage at 1x here, you may have a good quality assessment benchmark for optical slowmotion.

The video is very action packed in the original. I didn't expect any plugin to be successful with this shot. Football players was just an example to demonstrate the image breaking on the sides with the GPU on.