Agent Skills: ffmpeg-command-syntax

Complete FFmpeg command syntax reference covering option ordering, input vs output options, stream specifiers, and position-sensitive options. PROACTIVELY activate for: (1) Command syntax questions, (2) Option placement issues, (3) Input vs output option confusion, (4) Stream specifier syntax, (5) -ss/-t/-to position questions, (6) Global vs per-file options, (7) Multiple input/output handling, (8) Option order errors. Provides: Correct option placement rules, input-only vs output-only options, position-sensitive option behavior, stream specifier syntax, common mistakes and fixes.