How to compress a video without losing quality?

True lossless compression isn't possible, but "visually lossless" compression is. With FFmpeg H.264, use `-crf 18` (visually lossless quality). For H.265, use `-crf 20`. Combine with `-preset slow` for better compression ratio. The file will be 30-50% smaller than the original with no visible quality loss. For archival, use `-crf 0` for mathematically lossless compression (files will be huge).

What is CRF in FFmpeg?

CRF (Constant Rate Factor) is a quality setting in x264/x265 encoders. Lower values = higher quality and larger files; higher values = lower quality and smaller files. Recommended ranges: 18 (visually lossless), 23 (default, good balance), 28 (high compression). CRF 18-23 is suitable for most use cases. CRF is the recommended rate control for archival and delivery.

Should I use H.264 or H.265 for compression?

H.265 (HEVC) is 30-50% more efficient than H.264 at the same quality, but has narrower browser support (no native support in Chrome/Firefox without hardware decoding). For broad compatibility (web, mobile, older devices), use H.264. For archival or modern devices (Apple ecosystem, 4K players), use H.265. For modern web and streaming, consider AV1.

Why is my compressed video still large?

Common reasons: 1.CRF too low (use 23-28 for compression); 2.Preset too fast (use `medium` or `slow`); 3.High resolution (downscale to 1080p or 720p); 4.High frame rate (60fps requires much more data than 30fps); 5.High bitrate audio (use 128kbps AAC, not 320kbps). Check the actual bitrate with `ffprobe` to diagnose.

What bitrate should I use for 1080p video?

Recommended bitrates for H.264: 1080p 30fps → 5-8 Mbps (general), 8-12 Mbps (high quality); 1080p 60fps → 8-12 Mbps (general), 12-18 Mbps (high quality). Use CRF instead of fixed bitrate when possible, as CRF adapts to content complexity. For streaming with bandwidth limits, use `-maxrate` and `-bufsize` to cap peak bitrate.

Video Compression Complete Guide: From Principles to FFmpeg Practical Use

A 1GB video file can often be compressed to 200MB with no visible quality loss. The trick is understanding how compression works and choosing the right parameters. This guide covers the principles of video compression and provides practical FFmpeg commands for various scenarios.

Why videos can be compressed

Raw video is enormous. One minute of uncompressed 1080p 30fps video is about 6GB. The fact that we can stream 4K movies over 25 Mbps connections is thanks to compression algorithms that exploit three types of redundancy:

1. Spatial redundancy (within a frame)

A blue sky has many pixels of nearly identical color. Instead of storing each pixel, compression stores the color once and references it. This is intra-frame compression (similar to JPEG for images).

2. Temporal redundancy (between frames)

Consecutive frames are usually similar. A talking-head video has the same background for minutes. Compression stores key frames (I-frames) fully and only the differences (P-frames, B-frames) for other frames. This is inter-frame compression.

3. Perceptual redundancy (human vision limits)

Human eyes are more sensitive to brightness than color, and to low frequencies than high frequencies. Compression discards data we can't perceive (chroma subsampling, quantization).

Modern codecs (H.264, H.265, AV1) use all three techniques plus advanced prediction algorithms.

Key concepts

I-frame, P-frame, B-frame

I-frame (Intra-coded): Complete frame, like a JPEG image
P-frame (Predictive): Stores only differences from previous frame
B-frame (Bi-directional): Stores differences from both previous and next frames

A typical GOP (Group of Pictures) is IBBPBBPBBPBB... with one I-frame every 2 seconds.

Bitrate vs CRF

Bitrate (CBR/VBR): Fixed or variable data rate. Predictable file size but quality varies.
CRF (Constant Rate Factor): Fixed quality, variable bitrate. Recommended for archival and delivery.

GOP (Group of Pictures)

GOP is the distance between I-frames. For streaming, use 2-second GOP (60 frames at 30fps). For archival, use 10-second GOP for better compression.

Codec comparison

Codec	Compression	Encoding speed	Browser support	Hardware decoding	License
H.264	100% (baseline)	Fast	All	All devices	MPEG LA
H.265	130-150%	Medium	Safari, partial Chrome/Edge	Modern devices	Complex licensing
AV1	150-160%	Very slow	Chrome, Firefox, Edge (recent)	Latest devices only	Free

For codec details, see our H.264 vs H.265 vs AV1 Comparison.

FFmpeg compression commands

Basic compression (recommended)

bash

ffmpeg -i input.mp4 -c:v libx264 -crf 23 -preset medium -c:a aac -b:a 128k output.mp4

This is the universal starting point. CRF 23 is the default quality; adjust based on results.

High compression (smaller file)

bash

ffmpeg -i input.mp4 -c:v libx264 -crf 28 -preset slow -c:a aac -b:a 96k output.mp4

-crf 28: More aggressive compression
-preset slow: Better compression efficiency
-b:a 96k: Lower audio bitrate

Visually lossless (high quality)

bash

ffmpeg -i input.mp4 -c:v libx264 -crf 18 -preset slow -c:a aac -b:a 192k output.mp4

H.265 compression (best efficiency)

bash

ffmpeg -i input.mp4 -c:v libx265 -crf 28 -preset medium -c:a aac -b:a 128k output.mp4

H.265 at CRF 28 ≈ H.264 at CRF 23 in quality, but 30-50% smaller.

AV1 compression (modern, future-proof)

bash

# Using SVT-AV1 (faster than libaom)
ffmpeg -i input.mp4 -c:v libsvtav1 -crf 32 -preset 6 -c:a libopus -b:a 128k output.mkv

Two-pass encoding (for fixed bitrate)

bash

# Pass 1
ffmpeg -y -i input.mp4 -c:v libx264 -b:v 5M -pass 1 -an -f mp4 /dev/null

# Pass 2
ffmpeg -i input.mp4 -c:v libx264 -b:v 5M -pass 2 -c:a aac -b:a 128k output.mp4

Useful for streaming with bandwidth limits.

Resolution and frame rate

Downscale for smaller files

bash

# 1080p to 720p
ffmpeg -i input.mp4 -vf "scale=-1:720" -c:v libx264 -crf 23 -c:a aac output.mp4

# 4K to 1080p
ffmpeg -i input.mp4 -vf "scale=-1:1080" -c:v libx264 -crf 23 -c:a aac output.mp4

Reduce frame rate

bash

# 60fps to 30fps
ffmpeg -i input.mp4 -r 30 -c:v libx264 -crf 23 -c:a aac output.mp4

Resolution and frame rate reductions cut file size significantly with minimal perceived quality loss for most content.

Bitrate reference table

Resolution	Frame rate	Recommended bitrate (H.264)	File size per minute
480p	30fps	1-1.5 Mbps	~10 MB
720p	30fps	2.5-4 Mbps	~25 MB
720p	60fps	3.5-5 Mbps	~35 MB
1080p	30fps	5-8 Mbps	~50 MB
1080p	60fps	8-12 Mbps	~75 MB
4K	30fps	20-35 Mbps	~250 MB
4K	60fps	35-50 Mbps	~400 MB

For H.265, multiply H.264 bitrate by 0.6-0.7 for same quality.

Preset comparison

Preset	Encoding speed	File size (same quality)	Use case
ultrafast	1x	1.5-2x larger	Live streaming
veryfast	1.5x	1.3x larger	Quick tests
fast	2x	1.2x larger	Casual use
medium (default)	3x	1.0x (baseline)	General use
slow	6x	0.9x smaller	Archival
veryslow	12x	0.85x smaller	Final delivery
placebo	30x+	0.83x smaller	Not recommended

The slow preset is the sweet spot for archival — 2x slower than medium but ~10% smaller files.

Audio compression

Audio is often overlooked but can affect file size:

bash

# Standard quality (recommended)
-c:a aac -b:a 128k

# High quality
-c:a aac -b:a 192k

# Voice only
-c:a aac -b:a 64k

# Maximum compression
-c:a libopus -b:a 96k

For most videos, 128kbps AAC is sufficient. Voice-only content can use 64kbps.

Hardware acceleration

NVIDIA NVENC

bash

ffmpeg -i input.mp4 -c:v h264_nvenc -preset p4 -cq 23 -c:a aac output.mp4

Intel QuickSync

bash

ffmpeg -i input.mp4 -c:v h264_qsv -global_quality 23 -c:a aac output.mp4

AMD AMF

bash

ffmpeg -i input.mp4 -c:v h264_amf -quality balanced -c:a aac output.mp4

Hardware encoders are 5-10x faster than software but produce slightly larger files at the same quality.

Common issues

Issue	Cause	Solution
File still large after compression	CRF too low or resolution too high	Use CRF 28, downscale to 1080p
Quality too poor	CRF too high	Use CRF 18-23
Encoding too slow	Preset too slow	Use `-preset medium` or `fast`
Audio sync issues	Variable frame rate source	Add `-vsync 0`
File won't play	Codec not supported	Use H.264 + AAC in MP4
Encoding errors	Insufficient memory	Use `-preset fast`

Summary

Video compression is about finding the right balance between quality and file size. Key takeaways:

Universal starting command: ffmpeg -i input.mp4 -c:v libx264 -crf 23 -preset medium -c:a aac -b:a 128k output.mp4
Adjust CRF: 18 (visually lossless), 23 (default), 28 (high compression)
H.265 saves 30-50% over H.264 at same quality
Downscale resolution for dramatic file size reduction
Use medium or slow preset for archival

For more FFmpeg commands, see our FFmpeg Getting Started Tutorial.

Quick reference:

CRF values: 18 (high), 23 (default), 28 (compressed)
Presets: medium (general), slow (archival), fast (testing)
H.265 vs H.264: H.265 is 30-50% smaller at same quality
Hardware encoding: NVENC, QuickSync, AMF for speed

Video Compression Complete Guide: From Principles to FFmpeg Practical Use ​

Why videos can be compressed ​

1. Spatial redundancy (within a frame) ​

2. Temporal redundancy (between frames) ​

3. Perceptual redundancy (human vision limits) ​

Key concepts ​

I-frame, P-frame, B-frame ​

Bitrate vs CRF ​

GOP (Group of Pictures) ​

Codec comparison ​

FFmpeg compression commands ​

Basic compression (recommended) ​

High compression (smaller file) ​

Visually lossless (high quality) ​

H.265 compression (best efficiency) ​

AV1 compression (modern, future-proof) ​

Two-pass encoding (for fixed bitrate) ​

Resolution and frame rate ​

Downscale for smaller files ​

Reduce frame rate ​

Bitrate reference table ​

Preset comparison ​

Audio compression ​

Hardware acceleration ​

NVIDIA NVENC ​

Intel QuickSync ​

AMD AMF ​

Common issues ​

Summary ​

References ​

Video Compression Complete Guide: From Principles to FFmpeg Practical Use

Why videos can be compressed

1. Spatial redundancy (within a frame)

2. Temporal redundancy (between frames)

3. Perceptual redundancy (human vision limits)

Key concepts

I-frame, P-frame, B-frame

Bitrate vs CRF

GOP (Group of Pictures)

Codec comparison

FFmpeg compression commands

Basic compression (recommended)

High compression (smaller file)

Visually lossless (high quality)

H.265 compression (best efficiency)

AV1 compression (modern, future-proof)

Two-pass encoding (for fixed bitrate)

Resolution and frame rate

Downscale for smaller files

Reduce frame rate

Bitrate reference table

Preset comparison

Audio compression

Hardware acceleration

NVIDIA NVENC

Intel QuickSync

AMD AMF

Common issues

Summary

References