Aspect ratio math and timecode conversion, including proper NTSC drop-frame handling.
Aspect Ratio
Timecode / FPS
16:9
9:16
4:5
1:1
21:9
2.35:1
4:3
Custom
Fill in either field — the other locks to the selected ratio automatically.
Result
1920 × 1080 · ratio 16:9
Fit inside a frame (letterbox / pillarbox)
Content area & bars
—
Timecode → Frames
Frames → Timecode
Duration between two timecodes
Frames
—
Drop-frame 29.97 skips frame numbers :00 and :01 at the start of every minute except every 10th, to keep timecode honest against real clock time over long durations — that's the only mode here that isn't a flat frame-rate multiply.