FFmpeg

Quick Reference

ffmpeg [global options] -i <input> [output options] <output>

FFmpeg figures out formats from file extensions. Most of the work is specifying codecs, quality, and filters.

Common Conversions

Video format conversion

# MKV to MP4 (re-encode)
ffmpeg -i input.mkv output.mp4

# MKV to MP4 (copy streams — fast, no quality loss)
ffmpeg -i input.mkv -c copy output.mp4

# MOV to MP4
ffmpeg -i input.mov -c:v libx264 -c:a aac output.mp4

-c copy copies streams without re-encoding. Use this when you just need a container change — it’s instant and lossless. It fails if the target container doesn’t support the source codecs.

Audio extraction

# Extract audio as-is
ffmpeg -i video.mp4 -vn -c:a copy audio.aac

# Extract and convert to MP3
ffmpeg -i video.mp4 -vn -q:a 2 audio.mp3

# Extract and convert to FLAC
ffmpeg -i video.mp4 -vn audio.flac

-vn = no video. -q:a 2 = variable bitrate quality (0=best, 9=worst for MP3).

Audio conversion

# WAV to MP3
ffmpeg -i input.wav -b:a 320k output.mp3

# FLAC to MP3
ffmpeg -i input.flac -b:a 320k output.mp3

# MP3 to OGG
ffmpeg -i input.mp3 -c:a libvorbis -q:a 6 output.ogg

Trimming and Cutting

# Cut from 00:01:30 to 00:04:00
ffmpeg -i input.mp4 -ss 00:01:30 -to 00:04:00 -c copy output.mp4

# Cut 90 seconds starting at 00:01:30
ffmpeg -i input.mp4 -ss 00:01:30 -t 90 -c copy output.mp4

-ss = start time. -to = end time. -t = duration. Placing -ss before -i seeks faster (input seeking) but can be less accurate at keyframes.

Resizing and Scaling

# Scale to 1280x720
ffmpeg -i input.mp4 -vf scale=1280:720 output.mp4

# Scale width to 1280, auto-calculate height (keep aspect ratio)
ffmpeg -i input.mp4 -vf scale=1280:-2 output.mp4

# Scale to 50%
ffmpeg -i input.mp4 -vf scale=iw/2:ih/2 output.mp4

Use -2 instead of -1 for auto-dimension — it rounds to even numbers, which many codecs require.

Quality and Encoding

H.264 (libx264)

# CRF mode (constant quality) — lower = better, 18-28 is sane range
ffmpeg -i input.mp4 -c:v libx264 -crf 23 -preset medium output.mp4

# Presets: ultrafast, superfast, veryfast, faster, fast, medium, slow, slower, veryslow
# Slower presets = better compression at same quality = smaller files = longer encode

H.265/HEVC (libx265)

ffmpeg -i input.mp4 -c:v libx265 -crf 28 output.mp4

~50% smaller files than H.264 at similar quality. Slower to encode. CRF scale differs — 28 in H.265 is roughly equivalent to 23 in H.264.

Useful Options

Flag	Purpose
`-c:v`	Video codec (`libx264`, `libx265`, `copy`)
`-c:a`	Audio codec (`aac`, `libmp3lame`, `copy`)
`-c copy`	Copy all streams (no re-encoding)
`-b:v 5M`	Video bitrate
`-b:a 320k`	Audio bitrate
`-r 30`	Output frame rate
`-an`	Strip audio
`-vn`	Strip video
`-sn`	Strip subtitles
`-y`	Overwrite output without asking
`-n`	Never overwrite
`-map 0`	Include all streams from first input
`-metadata title="Name"`	Set metadata

Recipes

Create GIF from video

ffmpeg -i input.mp4 -ss 5 -t 3 -vf "fps=15,scale=480:-2" -loop 0 output.gif

Add subtitles (burn in)

ffmpeg -i input.mp4 -vf subtitles=subs.srt output.mp4

Concatenate files

Create a text file list.txt:

file 'part1.mp4'
file 'part2.mp4'
file 'part3.mp4'

ffmpeg -f concat -safe 0 -i list.txt -c copy output.mp4

Extract frames

# One frame per second
ffmpeg -i input.mp4 -vf fps=1 frame_%04d.png

# Single frame at timestamp
ffmpeg -i input.mp4 -ss 00:00:30 -frames:v 1 thumbnail.png

Compress for web

ffmpeg -i input.mp4 -c:v libx264 -crf 28 -preset slow -c:a aac -b:a 128k -movflags +faststart output.mp4

-movflags +faststart moves the metadata to the beginning of the file so browsers can start playing before the full download.

Probe / Inspect

# Show file info
ffprobe input.mp4

# JSON output (detailed)
ffprobe -v quiet -print_format json -show_format -show_streams input.mp4

# Just duration
ffprobe -v quiet -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 input.mp4