So yes, Marco. The PNG movie exported from VP18 works in vMix. Historically, they have for me, so it must have been something that was resolved with a reboot, or something. I also had a temporary issue with MP4 renders not playing in VLC, Quicktime, and other players. That too was resolved without doing anything.

Animation renders do not seem to carry the alpha channel, and I believe that is a limitation of Vegas Pro.

Thanks for taking the time to help.

I may be forgetul, but I don't recall Quicktime Animation for Windows (qt7) having alpha support, only Mac. I see that vMIX also supports AVI.

Also, temporary, non-duplicable errors in opening files are almost always explainable by something other than software errors. Going forward, if you will post the file properties for your balky renders, @Marco. or one of the other experts here are often able to determine which settings were not compliant.

I use QT Animation codec created in After Effects with an alpha channel all of the time. I have not created an animation with alpha in Vegas though.

Anyway, despite being an old warhorse, QT Animation is not the best around. The RLE compression is ridiculously inefficient with motion source, and the rounding jitter is bad enough to show on the vectorscope.

Thank you all. Musicvid, thank you for the reference for posting properties. Here are the properties for one of the files that was rendered as a PNG sequence in VP18 which does not display alpha channel in vMix. To reiterate, using the same render preset now does work. So the problem was random.

[EDIT: Please note that Color Space is RGB. PNG sequences rendered before and after the random issue show Color Space as RGBA, including the alpha channel.]

- - - - -

General
Complete name                            : [NAME REDACTED]
Format                                   : MPEG-4
Format profile                           : QuickTime
Codec ID                                 : qt   2005.03 (qt  )
File size                                : 585 MiB
Duration                                 : 14 s 912 ms
Overall bit rate mode                    : Variable
Overall bit rate                         : 329 Mb/s
Encoded date                             : UTC 2021-09-29 03:31:09
Tagged date                              : UTC 2021-09-29 03:32:00
Writing library                          : Apple QuickTime

Video
ID                                       : 2
Format                                   : PNG
Format/Info                              : Portable Network Graphic
Compression                              : Deflate
Codec ID                                 : png 
Duration                                 : 14 s 912 ms
Source duration                          : 14 s 915 ms
Bit rate mode                            : Variable
Bit rate                                 : 329 Mb/s
Width                                    : 1 920 pixels
Height                                   : 1 080 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 29.970 (30000/1001) FPS
Color space                              : RGB
Bit depth                                : 8 bits
Compression mode                         : Lossless
Bits/(Pixel*Frame)                       : 5.296
Stream size                              : 585 MiB (100%)
Source stream size                       : 585 MiB (100%)
Language                                 : English
Encoded date                             : UTC 2021-09-29 03:25:38
Tagged date                              : UTC 2021-09-29 03:32:00

Audio
ID                                       : 1
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 14 s 912 ms
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                              : 233 KiB (0%)
Language                                 : English
Encoded date                             : UTC 2021-09-29 03:25:37
Tagged date                              : UTC 2021-09-29 03:32:00

So the problem was random.

That's an interesting account, but I don't recall ever getting different results from the same unaltered template.

Quite honestly, as I learned more about the program through experience, I found that the "random errors" in my output could also be explained by pebcac. Still true twenty years later...