When moving to the next video in the playlist, I rely on the timing of the transition to be just right, otherwise it will be very obvious to the viewer that I just played a new video instead of it looking like a smooth animation.

In vMix 11, this was no problem. The playlist had perfect timing, and the whole thing looked really good. Ever since vMix 12, however, the end of the video is cut off by a fraction of a second.

This seems to happen on all codecs to some degree. Ffdshow is completely off and LAV misses off the fraction of a second, same with CoreAVC. The Microsoft codec jitters at the very start, making it less usable, but it does at least appear to get its timing right.

Any ideas on how to sort this out?

The file format is MP4.

Very strangely, having messed with the settings on the Performance page (synchronise output with refresh rate enabled, video renderer set to VMR9, low latency capture enabled), it seems to work as it did in version 11. I appreciate that frame perfect transitions are not generally possible - in fact, I didn't really expect it to work in 11 either. The fact that it did though made me want to keep that functionality.

I'm going to leave those settings well alone now. I'm subscribing to my age old computing philosophy that if it works, and you don't know why, leave it well alone! I reckon it may have been the video renderer though, as you said.

Now I'd like if I may to hijack my own thread a little and ask about some regressions in XAML support. In version 11, I had a looping video made using Expression Blend and its timeline functionality. It does not loop in version 12, and indeed timeline support in general seems a little touch and go. If you want, I can PM you one such example of something that doesn't work, despite playing fine in Blend.

Ah. I just found the documentation that says that. Well that solves all my problems, so I went ahead and bought a copy of vMix HD. Have a beer on me.