To use any frame memory channel as a matte channel, you need to program that channel as a key channel. Most people map their main V/K Pair assignments with FM 1 as the fill, FM 2 as the key, FM 3 as fill, FM 4 as key, etc. But they often neglect to include the odd FM's (1,3,5,7) as potential keyer sources. I map FM 2 as the key for FM 1, but I then also map FM 1 as the hole-cutter for FM 2. The reason for doing this is because when you try to do a split key (which is what you are trying to accomplish with your question), you can only split to a source that has been mapped as a key source...otherwise it will not appear in your cross points as a potential split source. Once you have done this, the procedure to split your key is this: select your fill source (your VT or camera) on the keyer bus. Then either delegate this keyer (eg. M/E 2 Key 2) in the keyer panel & hold down the SPLIT button...your keyer row will show you your available hole-cut sources; while holding down the SPLIT button, select the source on the key bus that you want to be the hole-cutter (your FM playback channel). Alternatively, you can simple hold down the keyer delegation button in the keyer transition module & you will see your available keyer sources - keep holding down this button as you select your hole-cutter source (you can also use the SHIFT button to access all 64 buttons where it may be mapped). In either case, if you don't see the FM channel that you want, it means that it hasn't been mapped as a key source. Now, if your FM is playing back a black & white source it will be the hi-con for your selected fill source on that bus. By mapping ALL FM's into the key area (menu 7322.5), you can use any channel you want to be the hole-cutter, rather than being limited to even-numbered channels.