Originally published at ffmpeg-micro.com

Trimming video with FFmpeg looks simple until your 5-second clip comes out as 7 seconds. Or your output starts a few frames late. The culprit is almost always flag order: where you put -ss relative to -i completely changes how FFmpeg processes the seek.

This post covers what -ss , -t , and -to do, why their placement matters, and when to use each combination.

What -ss, -t, and -to Actually Do

Three flags control timing in FFmpeg:

-ss sets the start position (the seek point)

-t sets the duration of the output

-to sets the end timestamp

-t and -to are mutually exclusive. If you use both, -t wins and -to gets ignored silently.

The critical distinction is where you place -ss : before -i (input seeking) or after -i (output seeking). The two produce different results with different tradeoffs.

Input Seeking: Fast but Imprecise

Place -ss before -i and FFmpeg jumps directly to the nearest keyframe at or before your timestamp.…