This is a known issue with Blackmagic devices using Mercury Transmit. The same issue occurs in Premiere Pro with sequences that use non-standard frame formats (dimensions + PAR + frame rate).
A difference between the previous (QuickTime or DirectShow) video preview technology and Mercury Transmit is that the old technology required the user to specify the frame format to send to the video preview device from a list of supported frame formats, while Mercury Transmit negotiates with the device to choose the best-matching frame format for output. In either case, After Effects scales the video preview image to the resulting frame format.
With Mercury Transmit this frame format negotiation works as expected with most video preview devices, including using a monitor connected to your display card as the video preview monitor. Blackmagic devices are different: when the comp does not exactly match a frame format supported by the device, an error is returned (internally, as allowed by the Mercury Transmit API) instead of a list of frame formats that After Effects could transform the comp to, and therefore no output occurs.
This is noted along with other known issues and information about how video preview with Mercury Transmit works in After Effects CC 2014 here:
So to clarify Tim, are we forced into using Mercury Transmit for video previews or do we get an option to use our Blackmagic devices with the "previous Quicktime video preview technology"?
Whilst the automatic negotiation in Mercury Transmit works well with the standard video presets it does not appear to work for those of us who live outside those presets.
QuickTime-based video preview has been removed from After Effects. It relied on a QuickTime API that Apple has deprecated, and calling this API was instigating After Effects CC (12.x) to crash under common circumstances. These were motivating factors for why QuickTime-based video preview was replaced with Mercury Transmit, and we are pleased that Mercury Transmit also provides additional functionality and performance improvements.
I want to repeat and clarify that Mercury Transmit is designed to handle non-standard frame formats, and that this works well with other Mercury Transmit devices. We talk with Blackmagic regularly and they are aware that this limitation occurs in how they choose to implement the Mercury Transmit API. We will continue to discuss this issue with them.
The best workaround I can advise for now is for you to nest your comp into a comp that uses a supported frame format. I realize that this is neither ideal or convenient, but it does put your frames onto the video preview monitor.
You're right, nesting a comp is neither ideal or convenient and is useless for any real-time interactions.
My next question is, why did you drop the "Scale and letterbox output to fit video monitor" option in Video Preview Preferences?
Mercury Transmit only scales to fit the monitor's pixel height and it respects the comp's aspect ratio. Even a 16 x 16 pixel comp previews as a square comp with black bars either side so surely it's possible for Mercury Transmit to be tweaked to accomodate the scale and letterbox option.
I appreciate that Mercury Transmit is the Adobe way forward and that it is up to Blackmagic to catch up but I'm disappointed that my investment in BMD hardware is no longer supported.
Bringing back the scale and letterbox option would certainly help those of us who like to work on pixel perfect odd size comps.
Can you be more specific about what your expectation is regarding scaling the video preview image? Do you wish to have a 1:1 pixel preview on the monitor? Or do you want the 16x16 comp to fill the entire video screen without black bars?
The Scale and Letterbox control is no longer necessary because Mercury Transmit negotiates the frame size with the video preview device. In the previous video preview technology, the user needed to choose the frame size, and the Scale and Letterbox control was necessary in case of mismatches between the chosen size and the comp size. As previously mentioned, Blackmagic does not currently support the automatic negotiation in Mercury Transmit, but we are hopeful that they will add this functionality in a future release of their drivers.
My expectation is that I have the option to toggle between a 1:1 pixel preview or scale to fill the monitor whilst maintaining the comp's aspect ratio.
To use the 16x16 comp as an example, assuming I'm using a 1920x1080 monitor for previews I would expect it scale to 1080x1080 with black bars either side.
At present Mercury Transmit seems to upscale and downscale as expected but lacks the option to toggle the scaling on and off.
Hopefully you'll be able to fix the "Scale and letterbox output to fit video monitor" option and we can use Mercury Transmit for previews from After Effects in the same way as we have for as long as I can remember.
Only time will tell if Mercury Transmit can match the performance of the Blackmagic cards.
Thanks for the explanation. I've made note of this, but please do submit 1:1 pixel preview as a feature request: http://adobe.ly/feature_request
For this to work, Mercury Transmit will need to be able to matte the comp inside of a larger frame matching the monitor's native format. This starts to get tricky because Mercury Transmit isn't necessarily aware of the native resolution of the monitor that's connected to the video preview device, with the exception of using a 2nd monitor as the preview device. It's far from impossible, but a little more work than may be obvious.
Regarding performance with Mercury Transmit, you can certainly test that now with your Blackmagic device as long as you're using a supported frame format. In my tests I was getting anywhere from 25-400% better performance (in terms of RAM preview playback performance for high-bandwidth comps) than previous versions of After Effects, across a variety of scenarios, computers, and video preview devices. Try a 1920x1080 29.97fps comp at 32bpc; depending on your machine specs it will likely give less than real-time RAM preview playback, but better results in After Effects CC 2014 (13.0) than previous versions. Try it using both your Blackmagic device and using a 2nd monitor as the video preview device.
Hi Paul, hi Tim
I already posted this myself but I just want to add my opinion here as well:
With AJA Kona scaling a larger project (like Scope) down to the monitor resolution (HD or 2K) works perfectly using Mercury.
With BM not at all. But they can do it with Resolve where actually any format is output to HD using the same BM card.
For me as well this is a very very important thing because working with Scope or bigger resolutions for retouch work needs monitoring on external reference Monitors.
For the moment I am using my second system monitor to preview larger comps. To get it to my reference monitor or the big screen I do nesting as well...
The suggestion to nest comps is good in theory but this does not work in practice.
For instance the reason I noticed a problem in the first place is I use the default Adobe HDV/HDTV 720 25p comp. I use this all the time and prior to AE CC2014 I was able to output this through my Blackmagic Intensity Pro to a JVC pro monitor at Blackmagic HD 720 50. I never had an issue with this. As an aside it does seem strange that there is no default 50p setting in AE but that's another story.
So when I opened an old project in the new version of AECC2014 with Mercury Transmit, I was surprised that I g0t a black screen, basically no output. So I checked a few things on line and worked out that to do it I needed Blackmagic to have a 25p setting which it doesn't have.
So to fix the issue I knew I needed to output a 1280x720 50p comp to the timeline. So I go into the HDV/HDTV 720 25p comp settings ( remember these are the default settings in AE there is no 50p) and change to 50p. Trouble is even though I have 25p targa sequence which plays perfectly when dropped in the 50p timeline, I had some composited elements that now float because for every frame of the targa sequence AE is now squeezing 2 frames into that space.
So my next thought was your suggestion of nesting. But this too does not work. A 25p timeline inside a 50p timeline shows the same floating problem. Even if I switch the Collapse Transformations it still does not work. I get a video field look for my composited elements, whereas my background is 25p.
I have made note about this on the Blackmagic site and I hope this issue can be resolved