How to Process Media Files with FFmpeg

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FFmpeg is the Swiss Army knife of media processing, capable of transcoding, streaming, filtering, and manipulating virtually any audio/video format. This guide covers practical FFmpeg usage patterns f...

Why FFmpeg

FFmpeg powers most video platforms:

Universal Format Support: Handles virtually every codec and container
Powerful Filters: Resize, crop, overlay, color-correct, and more
Streaming Capable: RTMP, HLS, DASH output
Subtitle Support: Embed, extract, and render subtitles
Batch Processing: Script any media workflow

Installation

# Ubuntu/Debian
sudo apt install ffmpeg
# CentOS/RHEL
sudo dnf install ffmpeg
# macOS
brew install ffmpeg
# Verify installation
ffmpeg -version

Basic Concepts

FFmpeg Command Structure

ffmpeg [global_options] [input_options] -i input [output_options] output

Container vs Codec

Container: File format (MP4, MKV, AVI)
Video Codec: Video compression (H.264, H.265, VP9)
Audio Codec: Audio compression (AAC, MP3, Opus)

Check file information:

ffprobe -v error -show_format -show_streams input.mp4

Common Transcoding Tasks

Convert Between Formats

# MKV to MP4 (re-encode)
ffmpeg -i input.mkv -c:v libx264 -c:a aac output.mp4
# MKV to MP4 (copy streams, no re-encoding)
ffmpeg -i input.mkv -c copy output.mp4
# AVI to WebM
ffmpeg -i input.avi -c:v libvpx-vp9 -c:a libopus output.webm

Change Video Quality

# Constant Rate Factor (CRF): Lower = better quality
# H.264: 18-28 is a good range; 23 is the default
ffmpeg -i input.mp4 -c:v libx264 -crf 23 output.mp4
# H.265 (HEVC): Better compression
ffmpeg -i input.mp4 -c:v libx265 -crf 28 output.mp4
# Target bitrate
ffmpeg -i input.mp4 -c:v libx264 -b:v 2M output.mp4
# Two-pass encoding (best quality for target size)
ffmpeg -i input.mp4 -c:v libx264 -b:v 2M -pass 1 -f null /dev/null
ffmpeg -i input.mp4 -c:v libx264 -b:v 2M -pass 2 output.mp4

Resize Video

# Scale to a specific resolution
ffmpeg -i input.mp4 -vf "scale=1280:720" output.mp4
# Scale while maintaining aspect ratio
ffmpeg -i input.mp4 -vf "scale=1280:-1" output.mp4 # Height auto
ffmpeg -i input.mp4 -vf "scale=-1:720" output.mp4 # Width auto
# Scale to fit within dimensions (padding if needed)
ffmpeg -i input.mp4 -vf "scale=1280:720:force_original_aspect_ratio=decrease,pad=1280:720:(ow-iw)/2:(oh-ih)/2" output.mp4

Working with Subtitles

Convert YouTube Subtitles to SRT

Convert YouTube's VTT format to SRT:

ffmpeg -i subtitles.vtt subtitles.srt

Embed Subtitles (Soft Subs)

Subtitles as a separate stream (can be toggled):

# Add SRT as a subtitle stream
ffmpeg -i video.mp4 -i subtitles.srt -c copy -c:s mov_text output.mp4
# Add VTT subtitles
ffmpeg -i video.mp4 -i subtitles.vtt -c copy -c:s webvtt output.mkv
# Multiple subtitle tracks
ffmpeg -i video.mp4 -i english.srt -i spanish.srt \
-c copy -c:s mov_text \
-metadata:s:s:0 language=eng \
-metadata:s:s:1 language=spa \
output.mp4

Burn Subtitles into Video (Hard Subs)

Subtitles rendered onto video (permanent):

# Burn SRT subtitles
ffmpeg -i video.mp4 -vf "subtitles=subtitles.srt" output.mp4
# Customize subtitle style
ffmpeg -i video.mp4 -vf "subtitles=subtitles.srt:force_style='FontSize=24,PrimaryColour=&H00FFFF&'" output.mp4
# Burn ASS/SSA subtitles (preserves styling)
ffmpeg -i video.mp4 -vf "ass=subtitles.ass" output.mp4

Extract Subtitles

# Extract the first subtitle stream
ffmpeg -i video.mkv -map 0:s:0 subtitles.srt
# Extract all subtitle streams
ffmpeg -i video.mkv -map 0:s subtitles_%d.srt

Audio Processing

Extract Audio

# Extract as MP3
ffmpeg -i video.mp4 -vn -c:a libmp3lame -q:a 2 audio.mp3
# Extract in the original format
ffmpeg -i video.mp4 -vn -c:a copy audio.aac

Change Audio

# Change audio codec
ffmpeg -i input.mp4 -c:v copy -c:a aac output.mp4
# Adjust volume
ffmpeg -i input.mp4 -filter:a "volume=1.5" output.mp4
# Normalize audio
ffmpeg -i input.mp4 -filter:a loudnorm output.mp4
# Remove audio
ffmpeg -i input.mp4 -an output.mp4

Replace Audio Track

ffmpeg -i video.mp4 -i audio.mp3 -c:v copy -c:a aac -map 0:v:0 -map 1:a:0 output.mp4

Cutting and Joining

Cut Video Segments

# Cut from 00:01:00 for 30 seconds
ffmpeg -i input.mp4 -ss 00:01:00 -t 30 -c copy output.mp4
# Cut from 00:01:00 to 00:02:30
ffmpeg -i input.mp4 -ss 00:01:00 -to 00:02:30 -c copy output.mp4
# Fast seek (put -ss before -i for large files)
ffmpeg -ss 00:01:00 -i input.mp4 -t 30 -c copy output.mp4

Concatenate Videos

Create file list videos.txt:

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

Join files:

# Same codec (no re-encoding)
ffmpeg -f concat -safe 0 -i videos.txt -c copy output.mp4
# Different codecs (re-encode)
ffmpeg -f concat -safe 0 -i videos.txt -c:v libx264 -c:a aac output.mp4

Video Filters

Common Filter Examples

# Crop video (width:height:x:y)
ffmpeg -i input.mp4 -vf "crop=640:480:100:50" output.mp4
# Rotate video
ffmpeg -i input.mp4 -vf "transpose=1" output.mp4 # 90° clockwise
ffmpeg -i input.mp4 -vf "transpose=2" output.mp4 # 90° counterclockwise
ffmpeg -i input.mp4 -vf "hflip" output.mp4 # Horizontal flip
ffmpeg -i input.mp4 -vf "vflip" output.mp4 # Vertical flip
# Speed up/slow down
ffmpeg -i input.mp4 -vf "setpts=0.5*PTS" -af "atempo=2.0" output.mp4 # 2x speed
ffmpeg -i input.mp4 -vf "setpts=2.0*PTS" -af "atempo=0.5" output.mp4 # 0.5x speed
# Add fade-in/out
ffmpeg -i input.mp4 -vf "fade=t=in:st=0:d=2,fade=t=out:st=58:d=2" output.mp4

Add Watermark/Overlay

# Image watermark in corner
ffmpeg -i video.mp4 -i watermark.png \
-filter_complex "overlay=W-w-10:H-h-10" \
output.mp4
# Text overlay
ffmpeg -i video.mp4 \
-vf "drawtext=text='Copyright 2024':fontsize=24:fontcolor=white:x=10:y=H-th-10" \
output.mp4
# Timestamp
ffmpeg -i video.mp4 \
-vf "drawtext=text='%{pts\:hms}':fontsize=24:fontcolor=white:x=10:y=10" \
output.mp4

Creating Thumbnails and GIFs

Extract Thumbnails

# Single frame at a specific time
ffmpeg -i video.mp4 -ss 00:00:10 -vframes 1 thumbnail.jpg
# Multiple thumbnails (every 10 seconds)
ffmpeg -i video.mp4 -vf "fps=1/10" thumbnail_%04d.jpg
# Thumbnail grid/sprite
ffmpeg -i video.mp4 -vf "fps=1/5,scale=160:-1,tile=5x5" sprite.jpg

Create GIF

# Basic GIF (large file)
ffmpeg -i video.mp4 -t 5 output.gif
# Optimized GIF with palette
ffmpeg -i video.mp4 -t 5 -vf "fps=15,scale=480:-1:flags=lanczos,palettegen" palette.png
ffmpeg -i video.mp4 -i palette.png -t 5 -filter_complex "fps=15,scale=480:-1:flags=lanczos[x];[x][1:v]paletteuse" output.gif

Streaming

Generate HLS for Adaptive Streaming

ffmpeg -i input.mp4 \
-c:v libx264 -c:a aac \
-hls_time 10 \
-hls_list_size 0 \
-hls_segment_filename "segment_%03d.ts" \
playlist.m3u8

Multiple Quality HLS

ffmpeg -i input.mp4 \
-filter_complex "[0:v]split=3[v1][v2][v3]; \
[v1]scale=1920:1080[v1out]; \
[v2]scale=1280:720[v2out]; \
[v3]scale=854:480[v3out]" \
-map "[v1out]" -map 0:a -c:v:0 libx264 -b:v:0 5M -c:a aac -b:a:0 192k \
-hls_time 10 -hls_playlist_type vod 1080p.m3u8 \
-map "[v2out]" -map 0:a -c:v:1 libx264 -b:v:1 2.5M -c:a aac -b:a:1 128k \
-hls_time 10 -hls_playlist_type vod 720p.m3u8 \
-map "[v3out]" -map 0:a -c:v:2 libx264 -b:v:2 1M -c:a aac -b:a:2 96k \
-hls_time 10 -hls_playlist_type vod 480p.m3u8

Batch Processing with Scripts

Bash Script Example

##!/bin/bash
INPUT_DIR="./raw"
OUTPUT_DIR="./processed"
mkdir -p "$OUTPUT_DIR"
for file in "$INPUT_DIR"/*.mp4; do
filename=$(basename "$file" .mp4)
echo "Processing: $filename"
ffmpeg -i "$file" \
-c:v libx264 -crf 23 \
-c:a aac -b:a 128k \
-vf "scale=1280:-1" \
"$OUTPUT_DIR/${filename}_720p.mp4"
done
echo "Done!"

Node.js Integration

const { spawn } = require('child_process');
function transcodeVideo(input, output, options = {}) {
return new Promise((resolve, reject) => {
const args = [
'-i', input,
'-c:v', 'libx264',
'-crf', options.crf || '23',
'-c:a', 'aac',
'-y', // Overwrite output
output
];
const ffmpeg = spawn('ffmpeg', args);
ffmpeg.stderr.on('data', (data) => {
console.log(`FFmpeg: ${data}`);
});
ffmpeg.on('close', (code) => {
if (code === 0) {
resolve(output);
} else {
reject(new Error(`FFmpeg exited with code ${code}`));
}
});
});
}
// Usage
transcodeVideo('input.mp4', 'output.mp4', { crf: '28' })
.then(output => console.log('Created:', output))
.catch(err => console.error('Error:', err));

Key Takeaways

Use -c copy when possible: Avoid re-encoding for speed
CRF for quality control: Lower values = higher quality
Two-pass for target size: Best quality at a specific bitrate
Palette for GIFs: Essential for good quality
-ss before -i: Faster seeking in large files
Test on short clips: Prototype filters before full renders

FFmpeg's depth is vast—these patterns cover most common needs, but the documentation reveals countless more capabilities for specialized workflows.

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How to Process Media Files with FFmpeg

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How to Process Media Files with FFmpeg

Why FFmpeg

Installation

Basic Concepts

FFmpeg Command Structure

Container vs Codec

Common Transcoding Tasks

Convert Between Formats

Change Video Quality

Resize Video

Working with Subtitles

Convert YouTube Subtitles to SRT

Embed Subtitles (Soft Subs)

Burn Subtitles into Video (Hard Subs)

Extract Subtitles

Audio Processing

Extract Audio

Change Audio

Replace Audio Track

Cutting and Joining

Cut Video Segments

Concatenate Videos

Video Filters

Common Filter Examples

Add Watermark/Overlay

Creating Thumbnails and GIFs

Extract Thumbnails

Create GIF

Streaming

Generate HLS for Adaptive Streaming

Multiple Quality HLS

Batch Processing with Scripts

Bash Script Example

Node.js Integration

Key Takeaways