FFmpeg

Input Seeking (Major Difference)

• -ss BEFORE -i: fast seek, may be inaccurate—starts from nearest keyframe
• -ss AFTER -i: frame-accurate but slow—decodes from start
• Combine both: -ss 00:30:00 -i input.mp4 -ss 00:00:05—fast seek then accurate trim
• For cutting, add -avoid_negative_ts make_zero to fix timestamp issues

Stream Selection

• Default: first video + first audio—may not be what you want
• Explicit selection: -map 0:v:0 -map 0:a:1—first video, second audio
• All streams of type: -map 0:a—all audio streams
• Copy specific: -map 0 -c copy—all streams, no re-encoding
• Exclude: -map 0 -map -0:s—all except subtitles

Encoding Quality

• CRF (Constant Rate Factor): lower = better quality, larger file—18-23 typical for H.264
• -preset: ultrafast to veryslow—slower = smaller file at same quality