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egopost: convert NVDEC frames to yuv420p before RGB - #1336
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NVDEC (h264_cuvid, vp9_cuvid) returns NV12. swscale converts NV12 to RGB by a different path than the yuv420p the software decoders produce, even though the decoded YUV is identical (H.264 decoding is bit exact). On the README example the FFmpeg runtime's RGB frames therefore differed from the OpenCV path by 0.77/255 on average (up to 33), and the model amplified that into a 0.35 mm mean vertex difference (up to 6.4 mm) and different detector boxes. Convert NVDEC frames to yuv420p first, then to RGB, for the *_cuvid decoders. The frames then match the software path bit for bit, and with matching library versions the pipeline output is identical to a run on the OpenCV path (boxes identical, hand poses bit-identical, other arrays within 4e-7). The software decoders are unchanged. Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Signed-off-by: Shao Su <shaoxiangs@nvidia.com>
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Description
NVDEC (h264_cuvid, vp9_cuvid) returns NV12. swscale converts NV12 to RGB by a different path than the yuv420p the software decoders produce, even though the decoded YUV is identical (H.264 decoding is bit exact). On the README example the FFmpeg runtime's RGB frames therefore differed from the OpenCV path by 0.77/255 on average (up to 33), and the model amplified that into a 0.35 mm mean vertex difference (up to 6.4 mm) and different detector boxes.
Convert NVDEC frames to yuv420p first, then to RGB, for the *_cuvid decoders. The frames then match the software path bit for bit, and with matching library versions the pipeline output is identical to a run on the OpenCV path (boxes identical, hand poses bit-identical, other arrays within 4e-7). The software decoders are unchanged.
Fixes #(issue)
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Testing
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SKIP=check-copyright-year pre-commit run --all-filesgit commit -s) per the DCO