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Newer ffmpeg releases refuse to encode JPEG from limited-range video frames, so poster frames failed on CI's ffmpeg while older versions accepted the same command. The poster is converted to full-range yuvj420p before encoding, which every supported ffmpeg version takes. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01MRtGG9ARfqqhma3t85Ro2u