Video Editor - FFmpeg & Encoding Expert

Expert guidance for video editing, encoding, and processing with ffmpeg. This skill covers container formats, codecs, encoding best practices, and quality optimization for video production workflows.

When to Use This Skill

Use this skill when:

• Encoding or transcoding video files
• Converting between container formats (MKV, MP4, etc.)
• Optimizing encoding settings for quality or file size
• Troubleshooting video quality issues
• Working with color spaces and color matrices
• Hardsubbing or softsubbing videos
• Preparing videos for specific platforms or devices
• Understanding why a video looks wrong after processing

Core Concepts

Container vs. Codec

This distinction is critical. File extensions like .mkv or .mp4 are container formats that package already-compressed streams. The actual compression happens through codecs like H.264, H.265, VP9, or AV1.

Concept	What It Is	Examples
Container	Wrapper that holds video/audio/subtitle streams	MKV, MP4, AVI, MOV, WebM
Codec	Algorithm that compresses/decompresses video	H.264, H.265/HEVC, VP9, AV1
Encoder	Software that implements a codec	x264, x265, libvpx, NVENC

Remuxing vs. Reencoding

Operation	What It Does	Quality Impact	Speed
Remuxing	Moves streams between containers without re-compression	None (lossless)	Very fast
Reencoding	Decodes and re-encodes video with new settings	Always loses quality	Slow

Rule of thumb: If you only need to change the container format, remux. Only reencode when absolutely necessary.

Quality Principles

What "Quality" Actually Means

Video quality measures how closely the output resembles the source. Every processing step moves the video further from the original. There is no way to add quality - only preserve or lose it.

Common Misconceptions

Myth	Reality
Higher resolution = better quality	Resolution is just dimensions; a 720p video can look better than a 4K one
Higher bitrate = better quality	Encoder efficiency matters more; same quality at different sizes is possible
H.265 is always 50% smaller	Depends on encoder settings; poorly-configured H.265 can be worse than H.264
Hardware encoding is fine for quality	Hardware encoders (NVENC, QuickSync) sacrifice quality for speed
AI upscaling improves quality	Upscaling adds artificial detail that wasn't in the source

The Encoding Quality Hierarchy

From most to least important:

1. Encoder settings (CRF, preset, tuning)
2. Encoder choice (x264/x265 vs. hardware encoders)
3. Codec (H.265 vs. H.264 vs. VP9)

Quick Reference: FFmpeg Commands

Remux (Change Container, No Quality Loss)

# MKV to MP4 (preserves all streams)
ffmpeg -i input.mkv -c copy output.mp4

# MP4 to MKV
ffmpeg -i input.mp4 -c copy output.mkv

Basic Encoding

# Encode with x264, copy audio
ffmpeg -i input.mkv -c:a copy -c:v libx264 -preset slower -crf 20 output.mkv

# Encode with x265
ffmpeg -i input.mkv -c:a copy -c:v libx265 -preset slower -crf 22 output.mkv

Quality-Focused Encoding

# High-quality x264 for animation
ffmpeg -i input.mkv -c:a copy -c:v libx264 -preset slower -crf 18 \
  -x264-params bframes=8 output.mkv

# High-quality x265
ffmpeg -i input.mkv -c:a copy -c:v libx265 -preset slower -crf 20 \
  -x265-params bframes=8 output.mkv

Encoding Settings Deep Dive

CRF (Constant Rate Factor)

CRF controls quality vs. file size tradeoff. Lower = higher quality, larger file.

CRF Range	Quality Level	Typical Use
0	Lossless	Archival, intermediate
15-18	Visually lossless	High-quality archival
19-23	High quality	General use, streaming
24-28	Medium quality	Web, mobile
29+	Low quality	Previews, thumbnails

Note: CRF values aren't directly comparable between encoders. x265 CRF 22 ≈ x264 CRF 20.

Preset

Presets control encoding speed vs. compression efficiency.

Preset	Speed	File Size	Use When
ultrafast	Fastest	Largest	Live streaming
fast	Fast	Large	Quick transcodes
medium	Moderate	Moderate	Default
slow	Slow	Smaller	Quality-focused
slower	Very slow	Even smaller	Recommended for quality
veryslow	Extremely slow	Smallest	Maximum compression

Recommendation: Use slower for quality-focused encoding. The difference between slower and veryslow is minimal for significant time cost.

Tune Options

Tune	Best For
film	Live-action with film grain
animation	Cartoons, anime, flat areas
grain	Preserve film grain
stillimage	Slideshow, static content
fastdecode	Playback on weak devices

# Animation tuning
ffmpeg -i input.mkv -c:v libx264 -preset slower -crf 20 -tune animation output.mkv

Container-Specific Considerations

MKV (Matroska)

Pros:

• Supports virtually any codec
• Multiple audio/subtitle tracks
• Chapter markers
• Variable frame rate support

Cons:

• Less compatible with some devices/software
• Some streaming services don't accept it

MP4

Pros:

• Universal compatibility
• Web-friendly
• Hardware decoder support everywhere

Cons:

• Limited subtitle format support
• Stricter codec requirements
• Constant frame rate expected

Converting MKV to MP4 for Editing Software

Some editing software requires constant frame rate MP4. Use this two-pass approach:

# Step 1: Initial remux with timescale adjustment
ffmpeg -i input.mkv -c copy -video_track_timescale 24000 intermediate.mp4

# Step 2: Fix timestamps
ffmpeg -i intermediate.mp4 -c copy \
  -bsf:v "setts=dts=1001*round(DTS/1001):pts=1001*round(PTS/1001)" output.mp4

Color Space & Color Management

Understanding Color Metadata

Videos store colors in YCbCr format with metadata specifying:

• Color matrix: How to convert YCbCr to RGB (BT.709, BT.601)
• Color range: Limited (16-235) vs. Full (0-255)
• Chroma location: Where color samples are positioned

Common Issues

Symptom	Likely Cause
Washed out colors	Wrong color range (Limited treated as Full)
Crushed blacks/blown whites	Wrong color range (Full treated as Limited)
Greenish/pinkish tint	Wrong color matrix
Colors look "off" after encode	Mismatched color metadata

Preserving Color Information

# Explicitly preserve color metadata
ffmpeg -i input.mkv -c:v libx264 -preset slower -crf 20 \
  -colorspace bt709 -color_primaries bt709 -color_trc bt709 output.mkv

Hardsubbing (Burning In Subtitles)

Using FFmpeg

# Hardsub from external subtitle file
ffmpeg -i input.mkv -vf "subtitles=subs.ass" -c:v libx264 -preset slower -crf 20 output.mkv

# Hardsub from embedded subtitle track
ffmpeg -i input.mkv -vf "subtitles=input.mkv:si=0" -c:v libx264 -preset slower -crf 20 output.mkv

Using mpv (Better for Complex Subtitles)

mpv handles complex ASS subtitles (styling, positioning) more accurately:

mpv --no-config input.mkv -o output.mkv \
  --audio=no \
  --ovc=libx264 \
  --ovcopts=preset=slower,crf=20,bframes=8

What to Avoid

Tools

Tool	Problem
Handbrake	Unpredictable settings, hides important options
Online converters	Quality loss, privacy concerns
"AI upscalers"	Add fake detail, move further from source
Windows built-in tools	Poor quality, limited options

Practices

Practice	Why It's Bad
Unnecessary sharpening	Adds artifacts, moves from source
Upscaling to higher resolution	Doesn't add real detail
Multiple reencodes	Quality loss compounds
Using NVENC for quality	Hardware encoders prioritize speed over quality
Frame rate interpolation	Adds fake frames with artifacts

Recommended Tools

Essential

Tool	Purpose
ffmpeg	Swiss army knife for video processing
MediaInfo	Inspect video properties and metadata
mpv	Superior media player, encoding support
MKVToolNix	GUI for MKV muxing operations

Specialized

Tool	Purpose
Aegisub	Subtitle editing
HandBrake	Simple transcoding (use with caution)
yt-dlp	Download online videos

Troubleshooting

Video Won't Play

1. Check codec support on target device
2. Try remuxing to different container
3. Verify file isn't corrupted: ffmpeg -v error -i file.mkv -f null -

Colors Look Wrong After Encoding

1. Compare color metadata: mediainfo input.mkv vs. mediainfo output.mkv
2. Check color range (Limited vs. Full)
3. Check color matrix (BT.709 vs. BT.601)
4. Explicitly set color parameters in ffmpeg command

File Size Too Large

1. Increase CRF (e.g., 20 → 23)
2. Use slower preset for better compression
3. Consider x265 for better efficiency
4. Check if you're unnecessarily encoding (remux instead)

Encoding Takes Forever

1. Use faster preset (but accept larger file)
2. Check if hardware encoding is acceptable for your use case
3. Ensure source isn't being decoded unnecessarily

Audio/Video Out of Sync

1. Check source file for sync issues first
2. Use -async 1 for audio sync correction
3. Try remuxing instead of reencoding

Examples

Archive a Blu-ray Rip

ffmpeg -i input.mkv -c:a copy -c:v libx265 -preset slower -crf 18 \
  -x265-params bframes=8 output.mkv

Prepare for YouTube Upload

ffmpeg -i input.mkv -c:a aac -b:a 384k -c:v libx264 -preset slower -crf 18 \
  -profile:v high -level 4.2 -pix_fmt yuv420p output.mp4

Quick Preview/Proxy

ffmpeg -i input.mkv -c:a aac -b:a 128k -c:v libx264 -preset fast -crf 28 \
  -vf scale=640:-2 output.mp4

Extract Audio Only

# Copy audio stream (no re-encoding)
ffmpeg -i input.mkv -vn -c:a copy output.mka

# Convert to MP3
ffmpeg -i input.mkv -vn -c:a libmp3lame -b:a 320k output.mp3

Trim Without Re-encoding

# Trim from 1:00 to 2:30
ffmpeg -i input.mkv -ss 00:01:00 -to 00:02:30 -c copy output.mkv

Resources

• FFmpeg Documentation
• FFmpeg Wiki
• x264 Settings Guide
• x265 Settings Guide
• MediaInfo
• mpv Manual