Alpha Channel Video Dimensions

It's not hard to find videos that SAY they have an alpha channel. But

1. Just because a type of asset exists in Stock doesn't mean that normal contributors can submit them. There are many things that can't be submitted normally - like Photoshop templates, Audio, or Editorial photography (with no brand focus).

2. It's easy to find assets that claim things that aren't true. Like JPEGs claiming editable text, for example. This example claims to have an alpha channel but also claims to be H.264. Clearly one of these claims is fals, since H.264 does not support an alpha channel. It also seems inconcevable it could clock in at only 4 MB if it had an alpha channel.  I found another example: Loop gold glittering text change from 2022 to 2023 for new year change text shine flickering light effect animation on black background. isolated with alpha channel Prores 444 Stock Video | Adobe Stock specifically claims to use ProRes 444 in the description, but the summary says it is H.264. I am disinclined to try them out to see which is right. I do observe a number of videos precomposed with a uniform green. This is actually very useful, I have purchased such videos. As well as being usable in apps like Premiere Pro they can be used directly in OBS for broadcast overlays, just by adding a filter to the source.