Add optional cached-frame motion detection via cache_image flag #45
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Rob1in
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Rob1in
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LGTM. I like this option.
A question and note:
Question: is the issue here that the time between the two images is inconsistent, or that the interval is sometimes too short causing get_image(s) being called too quickly?
If stability is the issue: in this PR, the client of the vision service (event manager?) is responsible for maintaining a stable time interval between two frames for motion detection. But that still might not be that stable.
What about adding an asyncio.sleep() between two images (with a config attribute time_between_frames)? I like the idea of caching last_grey—maybe we could also cache a timestamp to detect inconsistent timing between images, if that’s the real issue.
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The main issue is that time delays don’t guarantee unique frames with RTSP. Even if you add a sleep, two get_image(s) calls can still return the same decoded frame because of buffering and codec behavior. So a delay helps sometimes, but it’s not reliable. Since I actually need guaranteed unique frames, that has to happen at the camera layer (block until a new frame or an I-frame). The cache_image option just avoids multiple rapid captures per RPC and compares frames across calls instead of within a single call, without relying on timing assumptions. |
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CI is green now; merging. Appreciate the feedback. |
adds an optional cache_image configuration flag to the Motion Detector vision service. When enabled, the service performs temporal differencing against a cached previous grayscale frame, so each GetDetections / GetClassifications call only captures one image instead of two.
Some cameras / pipelines are sensitive to multiple rapid captures per RPC call (latency, bandwidth, or frame timing issues). Caching the previous frame preserves the same motion-detection algorithm across calls rather than within a single call.