FFmpeg: A Practical Guide to Essential Command-Line Options

Introduction

FFmpeg is an incredibly versatile command-line tool for manipulating audio and video files. This post provides a practical collection of useful FFmpeg commands for common tasks.

FFmpeg Command Structure

The general structure of an FFmpeg command is:

ffmpeg [global_options] {[input_file_options] -i input_url} ... {[output_file_options] output_url} ...

Merging Video and Audio

Merging video and audio, with audio re-encoding

ffmpeg -i video.mp4 -i audio.wav -c:v copy -c:a aac output.mp4

Copying the audio without re-encoding

ffmpeg -i video.mp4 -i audio.wav -c copy output.mkv

Why copy audio?

1. Preserve Quality: Re-encoding can degrade audio quality. Copying preserves the original audio stream.
2. Speed: Copying is significantly faster than re-encoding.
3. Maintain Original Parameters: Avoids unintended changes to bitrate, sample rate, etc.

Replacing audio stream

ffmpeg -i video.mp4 -i audio.wav -c copy output.mkv

This is useful for dubbing or changing the soundtrack of a video.

Handling Different Audio/Video Durations

ffmpeg.exe -ss 00:00:10  -t 5 -i "video.mp4" -ss 0:00:01 -t 5 -i "music.m4a" -map 0:v:0 -map 1:a:0 -y "out.mp4"

The -shortest option ensures the output video’s duration matches the shorter of the input files. You can also use -t and -ss to specify precise start and end times for each input if needed.

ffmpeg -i "video.mp4" -i "music.m4a" -c:v copy -map 0:v:0 -map 1:a:0 -shortest "out.mp4"

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Video Format Conversion and Manipulation

Convert Video to MP4

ffmpeg -i input.avi output.mp4

Used when converting videos between formats.

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Extract Audio

ffmpeg -i input.mp4 -q:a 0 -map a output.mp3  # Highest quality audio
ffmpeg -i input.mp4 output.mp3 # Default quality

Convert Audio

ffmpeg -i input.wav output.mp3

Resize Video

ffmpeg -i input.mp4 -vf scale=1280:720 output.mp4  # 720p resolution

Trim Video (No Re-encoding)

ffmpeg -i input.mp4 -ss 00:00:30 -to 00:01:00 -c copy output.mp4

Reduce Video File Size (H.265 Encoding)

ffmpeg -i input.mp4 -vcodec libx265 -crf 28 output.mp4  # Adjust CRF value for quality/size tradeoff

A lower CRF value means higher quality (and larger file size).

Adjust Playback Speed

• Increase Speed (2x):

ffmpeg -i input.mp4 -filter:v "setpts=0.5*PTS" output.mp4

• Decrease Speed (0.5x):

ffmpeg -i input.mp4 -filter:v "setpts=2.0*PTS" output.mp4

Add Subtitles (Hardcoded)

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

Merge Multiple Videos

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

file_list.txt should contain a list of video file paths, one per line, like this:

file 'video1.mp4'
file 'video2.mp4'
file 'video3.mp4'

Extract a Frame as an Image

ffmpeg -i input.mp4 -ss 00:00:10 -vframes 1 output.png

Convert Images to Video

ffmpeg -framerate 30 -i image%03d.png -c:v libx264 output.mp4  # Assumes images are named image001.png, image002.png, etc.

Remove Audio

ffmpeg -i input.mp4 -an output.mp4

Extract Audio Segment

ffmpeg -i input.mp3 -ss 00:00:30 -to 00:01:00 -c copy output.mp3

Overlay Image (Watermark)

ffmpeg -i input.mp4 -i logo.png -filter_complex "overlay=10:10" output.mp4  # Adjust coordinates as needed

Change Frame Rate

ffmpeg -i input.mp4 -r 60 output.mp4

Convert to GIF

ffmpeg -i input.mp4 -vf "fps=10,scale=500:-1:flags=lanczos" output.gif  # Adjust fps and scale

Add Background Music

ffmpeg -i input.mp4 -i audio.mp3 -map 0:v -map 1:a -c:v copy -c:a aac output.mp4 # Consider adding -shortest if audio is longer

Rotate Video

ffmpeg -i input.mp4 -vf "transpose=1" output.mp4  # 90 degrees clockwise. Use 2 for counter-clockwise, 3 for 180 degrees.

Extract Video Without Audio

ffmpeg -i input.mp4 -vn -c:v copy output.mp4