The previous patch_decklink.py mixed v14_2_1 versioned types (Fix 1 renamed the allocator class) with no-ops for SetVideoInputFrameMemoryAllocator + QueryInterface-around-GetBytes (Fixes 2 & 3). That inconsistency compiled but silently dropped every video frame: VideoInputFrameArrived saw _v14_2_1 allocator output but tried to read it via the SDK 16 unversioned IDeckLinkVideoBuffer path, and the SDK released the buffer before FFmpeg could consume it.
Bisected with the BMD-provided Capture sample at SDK 16 mode 5 (Hp29) which got frames cleanly, confirming the signal was fine and the bug was in FFmpegs decklink demuxer.
Fix: pull libavdevice/decklink_{enc,dec,common}{.cpp,.h} from upstream FFmpeg master (commits past 7.1 that fully rename every decklink interface to its _v14_2_1 versioned form) and apply that diff in reverse during build. Now build is internally consistent and frames flow.
Verified: SDI1 recorder on zampp2 hits 423 frames in 14s @ 29 fps, ProRes HQ at 91 Mbps.
