Using External Mattes To help with tracking?

Hi there,
Autodesk Flame user here.
Is it possible for me to use external rendered Mattes (ie. from flame) into OFX to help me occulde the area i wish to do a track/meshwrap.

It would be great if that could be done, cause sometimes we have mattes done from other softwares.

Please advise on what the “how to” instructions would be.


You definitely should be able to.

  • Render the matte you want to use as an 8bit greyscale image
  • Launch Mocha
  • Create any shape
  • In layer properties, select the matte clip dropdown and import…
  • That should load a B&W matte as your new holdout layer

Please let me know if that works for you.


Hi Mary,
Thank you for your advise.

Right now i am just doing a test.
I am trying to track the BG and export the alembic data to change the BG behind the girl.

The footage i am working on is 3424x2202. I am working on my MBP2017, not the fastest with Radeon Pro 560X 4 GB
Intel UHD Graphics 630 1536 MB
But it seems to be Buggy:

  • doesn’t allow me to save.

  • when exiting to flame UI, it crashed Flame. (1st try)

  • the BG layer Track go weird (2nd try), then crashes Flame upon exiting mocha UI.
    -tried to resized to HD (crashed after stopping the track when it when offtrack)

  • I followed your instructions.

  • Fg is a girl which i first draw a mask around her, on first frame, then import the matte, holdout layer 1

  • draw the area behind her to track. layer 2 and put it below the holdout layer1.
    Do i have to change the blend mode to subtract?
    Only managed to track 10 frames out of 35 frames. and it crashed.

is it possible to link the alpha from the Flame Batch into the Mocha node insert/matte inputs, rather than using the import.

Thanks again for your time ,

No, you can’t link from Flame. However, what version of Mocha are you using?


Unfortunate that I can’t link from from.
This is the version I was ask to install for licensing issue.

Hi, Keith

Please use this installer instead:


Mocha should then successfully relaunch.

Best regards,

OK, I will have to circle back with Michael as to why you are on a pre-release, you should not be. Can you update to the latest release and see if it fixes the issue? Boris FX | Downloads

Ok! Thanks Mary!

Hi Mary,
I managed to update the latest version without any error.
I have to apologized as i realized I made a mistake in my test.
My alpha which i exported was on default ProRes 422 10 bit.
After exporting an 8 bit alpha, I am able to import the matte and use it.
Sorry for that!
And Thank you again for your help!


Ok, glad you’re all set!