fix(rendering): preserve chroma at odd frame edges

[yashranaway]

videos with an odd width or height lost the last row or column of colour data on the gpu path. the decoder copied the chroma planes using height / 2, the frame slicing did the same, and the gpu upload used width / 2, so for something like 17x9 the bottom and right edge got the wrong colour (a 1x1 frame came out green).

it now uses ffmpeg's own plane heights when copying and rounds up everywhere else, for both yuv420p and nv12, padded strides included. the cpu path already rounds up, so the two agree now. two tests cover it, one checks the copied planes and one compares gpu output against an even sized frame on llvmpipe. both fail on main.

🤖 Generated with Claude Code

Confidence Score: 5/5

The PR appears safe to merge; no actionable issues were found.

Summary

Preserves edge colors in odd-sized YUV420P and NV12 frames.

• Odd-sized YUV frames keep their edge color through GPU conversion.

No actionable issues found. Tests were reviewed but not run.

_{Reviews (1) · Last reviewed commit: "fix(rendering): preserve chroma at odd f..." · Reviewed by Greptile}

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[yashranaway]

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