{"schema":"record/v1","id":"art_01M5MRHP3SVN5YH4B21WGCCKSE","type":"article","revision":1,"etag":"\"r1.s0\"","title":"How is SMPTE LTC structured per libltc documentation and code, and where do 23.976, 29.97 and 59.94 behave differently?","summary":"libltc encodes LTC as 80-bit frames (2400 bit/s at 30 fps) with drop-frame at bit 10 and colour-frame at bit 11, and sets the drop-frame bit only when the frame rate rounds to 29.97 (rint(fps*100)==2997, in src/ltc.c); so 23.976 material is labelled as non-drop 24-frame counts (code reading).","status":"active","body":{"text":"libltc encodes LTC as 80-bit frames (2400 bit/s at 30 fps) with drop-frame at bit 10 and colour-frame at bit 11, and sets the drop-frame bit only when the frame rate rounds to 29.97 (rint(fps*100)==2997, in src/ltc.c); so 23.976 material is labelled as non-drop 24-frame counts (code reading).\n\nCurator qualifications: Specifications and code read 2026-10-22; no files written or decoded.\n\nLimitations: Specifications and code read 2026-10-22; no files written or decoded.\n\nEvidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.","citations":[{"url":"https://github.com/Ardour/manual/blob/9628c8bad094537fddd967ef137e8a692e2b1503/include/timecode-generators-and-slaves.html","note":"libltc bf84b010 src/ltc.h L100-L127 (documentation comments); libltc bf84b010 src/ltc.c L200-L206; libltc bf84b010 src/encoder.c (126 lines)"},{"url":"https://github.com/x42/libltc/blob/bf84b01097a1789c0296cc5fcfc3bf4608407930/src/ltc.h","note":"libltc bf84b010 src/ltc.h L100-L127 (documentation comments); libltc bf84b010 src/ltc.c L200-L206; libltc bf84b010 src/encoder.c (126 lines)"},{"url":"https://github.com/x42/libltc/blob/bf84b01097a1789c0296cc5fcfc3bf4608407930/src/timecode.c","note":"libltc bf84b010 src/ltc.h L100-L127 (documentation comments); libltc bf84b010 src/ltc.c L200-L206; libltc bf84b010 src/encoder.c (126 lines)"},{"url":"https://github.com/x42/libltc/blob/bf84b01097a1789c0296cc5fcfc3bf4608407930/src/encoder.c","note":"libltc bf84b010 src/ltc.h L100-L127 (documentation comments); 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so 23.976 material is labelled as non-drop 24-frame counts (code reading).\n\nCurator qualifications: Specifications and code read 2026-10-22; no files written or decoded.\n\nLimitations: Specifications and code read 2026-10-22; no files written or decoded.\n\nEvidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.","citations":[{"url":"https://github.com/Ardour/manual/blob/9628c8bad094537fddd967ef137e8a692e2b1503/include/timecode-generators-and-slaves.html","note":"libltc bf84b010 src/ltc.h L100-L127 (documentation comments); libltc bf84b010 src/ltc.c L200-L206; libltc bf84b010 src/encoder.c (126 lines)"},{"url":"https://github.com/x42/libltc/blob/bf84b01097a1789c0296cc5fcfc3bf4608407930/src/ltc.h","note":"libltc bf84b010 src/ltc.h L100-L127 (documentation comments); libltc bf84b010 src/ltc.c L200-L206; libltc bf84b010 src/encoder.c (126 lines)"},{"url":"https://github.com/x42/libltc/blob/bf84b01097a1789c0296cc5fcfc3bf4608407930/src/timecode.c","note":"libltc bf84b010 src/ltc.h L100-L127 (documentation comments); 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