ffmpeglisted

# FFmpeg Skill ## Hard rules 1. **Never overwrite the original.** Write to a new file. Derive the name if none given: `video.mp4` becomes `video_compressed.mp4`. Never use `-y` on the same path as the input. 2. **Never destroy quality.** Minimum floors: | Codec | Flag | Floor | Good default | |---|---|---|---| | H.264 (libx264) | `-crf` | 28 max | 18-23 | | H.265 (libx265) | `-crf` | 32 max | 24-28 | | VP9 (libvpx-vp9) | `-crf` | 40 max | 31-36 | | AAC | `-b:a` | 128k min | 192k | | MP3 | `-q:a` | 4 max | 2 | If the target size requires going below these floors, say so. Offer the best size achievable at the floor instead. 3. **File over 1 GB? Stop.** Say: "This file is [size]. Processing will take a while and produce large intermediates. Continue?" Only proceed with confirmation. ## Step 1 — Inspect first Always run this before building any command: ```bash ffprobe -v quiet -print_format json -show_format -show_streams "<input>" ``` Read the size, codec, resolution, bitrate, duration. Check the 1 GB rule here. ## Step 2 — Pick the right approach **Compression:** `libx264 -crf 23 -preset slow`. Copy audio unless asked otherwise: `-c:a copy`. **Format conversion:** If only the container changes, use `-c copy`. No re-encode. No quality loss. Instant. **Trimming:** `-ss` before `-i` for fast seek. `-c copy` when possible. **Audio extraction:** `-vn -c:a copy` to extract without re-encoding. **Scaling:** `-vf scale=1280:-2` to preserve aspec