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Aiden
2026-05-12 20:32:32 +10:00
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docs/DECKLINK_OPENGL_LESSONS_LEARNED.md
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@@ -282,6 +282,24 @@ Lesson:
- test policies such as `one_before_output` or `skip_before_output`
- prefer latest-input semantics over draining every pending upload
### CPU Input Conversion Can Be Worse Than Input Copy
When DeckLink input only exposed UYVY8 on the test machine, an initial CPU UYVY-to-BGRA conversion in the input callback measured around a full-frame budget on sampled runs and reduced input cadence dramatically.
Moving the input edge to raw UYVY8 capture changed the ownership:
- DeckLink callback copies raw supported input bytes into `InputFrameMailbox`
- the mailbox keeps latest-frame semantics and uses a contiguous copy when row strides match
- the render thread uploads/decodes UYVY8 into the shader-visible `gVideoInput` texture
- runtime shaders continue to see decoded input, not packed capture bytes
Lesson:
- keep input callbacks as capture/copy edges
- keep GL decode/upload in the render-owned path
- measure input copy, upload, and decode separately
- do not hide expensive format conversion inside the DeckLink callback
### Preview And Screenshot Must Stay Secondary
Preview is useful, but DeckLink output is the real-time path.