I updated Vegas to 22 (250), and the rendered file consisted entirely of black frames (the audio was fine).
I discovered that the problem was caused by the filter settings in Voukoder – previously, I had only set the output filters to BT709/XVYCC, and that worked in Vegas 21.
Now I have to set the input filters to BT709/XVYCC as well, and only then will the rendered file be correct.
So, the question is: are these settings correct and will the rendered file be correct?