Fairlight | Desktop Video | Interlaced playback bug.

Hi All

Replicated, as follows, on both my Windows PC and M1 Mac laptop.

With Davinci Resolve > Preferences > Video and Audio I/O set to:
Monitor device > Decklink Mini Monitor (Windows) or Utrastudio Monitor 3G (Mac)
and Audio I/O Engine > Desktop Video.

In the Fairlight Page, a 50i timeline plays back incorrectly, at 25 fields per second.
In the Edit Page, the same 50i timeline plays correctly at 25 frames per second.

With Monitor device still set to Decklink/Ultrastudio:
If I change my Audio I/O Engine preferences to anything other than 'Desktop Video', then playback speed in Fairlight is correct, even if the selected audio path ultimately routes to the Blackmagic output device... unless Monitor device > Mirror audio I/O engine output is enabled, in which case the Fairlight audio playback remains slow.

If I change my Video and Audio I/O preferences > Monitor device to None, playback speed in Fairlight is correct, regardless of Audio I/O Engine selection, again, even if the selected audio path ultimately routes to the Blackmagic output device.

So, as afar as I can tell, from my end it seems to be a bug related to Fairlight's handling of interlace timeline playback when Resolve is internally managing audio via the 'Desktop Video' Audio I/O Engine.

Cheers
Andy

I had no luck with getting assistance in my own time zone, so heres a little bump in the hope that I can get traction in someone else's! ;)

For further info, was seeing this on a Windows based 50i project, no such problems on the same system & setup with a 25p project. I opened the same project on my Mac (laptop) just now and am not seeing the same problem. I'll compare settings tomorrow, see if anything stands out.

Could it be a misinterpretation of the interlaced footage? DR normally deinterlaces 50i into 50p to preserve full temporal resolution, but the timeline needs to be set up for interlace and the source needs to be recognised as such (check the Clip Attributes). Throwing 50i into a 25p timeline and treating it as progressive is possible, but no pixel should ever change its position to avoid artefacts. Cuts could be problematic, though.
And then, which algorithm is in use? The 'neural' one is pretty good, but more demanding on the hardware. If it's actived, you could switch to the simple one until rendering.

Did a bit more digging and seem to have verified the issue I'm seeing with my project is not hardware and/or system specific... have replicated on both Mac and Windows.

In short, there seems to be a bug related to Fairlight's handling of interlaced timeline playback when Resolve is internally managing audio via the 'Desktop Video' Audio I/O Engine, either directly or via the 'Mirror audio I/O engine output' setting.

I've updated my first post accordingly.