Video Bitrate Explained: How It Affects Quality and File Size

What Is Video Bitrate?

Bitrate is the amount of data used to represent one second of video. It is measured in bits per second, typically expressed as kilobits per second (kbps) or megabits per second (Mbps). A video with a bitrate of 5 Mbps uses 5 million bits of data for every second of footage.

Bitrate is the single most important factor in determining video quality and file size. Double the bitrate, and you roughly double the file size. But the relationship between bitrate and perceived quality is not linear: going from 1 Mbps to 2 Mbps is a dramatic improvement, while going from 10 Mbps to 20 Mbps is barely noticeable.

Understanding how bitrate works is essential for anyone who converts, compresses, streams, or uploads video. This guide explains everything you need to know.

How Bitrate Affects Quality

Video codecs work by analyzing frames and discarding information that the human eye is unlikely to notice. At higher bitrates, the codec keeps more information and the result looks closer to the original. At lower bitrates, the codec must discard more, which introduces visible artifacts:

• Blocking/macroblocking: Grid-like patterns, especially in dark or gradient areas
• Banding: Smooth gradients turn into visible steps
• Mosquito noise: Flickering artifacts around sharp edges
• Smearing: Fine details like grass, hair, or text become blurry
• Color bleeding: Colors spread beyond their boundaries

The exact bitrate where artifacts become visible depends on the resolution, codec, frame rate, and content complexity.

Bitrate Modes: CBR, VBR, and CRF

Video encoders offer different bitrate control modes, each with distinct advantages.

Constant Bitrate (CBR)

CBR maintains the same bitrate throughout the entire video. Every second uses approximately the same amount of data, regardless of scene complexity.

# CBR encoding at 5 Mbps
ffmpeg -i input.mp4 -c:v libx264 -b:v 5M -minrate 5M -maxrate 5M \
  -bufsize 10M -c:a aac -b:a 192k output.mp4

Best for: Live streaming, hardware playback with limited buffers, broadcast.

Variable Bitrate (VBR)

VBR adjusts the bitrate dynamically based on scene complexity. Simple scenes (static backgrounds, talking heads) use less data, while complex scenes (action, fast motion) use more.

# VBR encoding with target 5 Mbps, max 8 Mbps
ffmpeg -i input.mp4 -c:v libx264 -b:v 5M -maxrate 8M \
  -bufsize 10M -c:a aac -b:a 192k output.mp4

Best for: Video files for download, archival, general purpose.

Constant Rate Factor (CRF)

CRF is a quality-targeted mode. Instead of specifying a bitrate, you specify a quality level and the encoder uses whatever bitrate is needed to achieve it. Lower CRF values mean higher quality and larger files.

# CRF encoding (quality-targeted)
ffmpeg -i input.mp4 -c:v libx264 -crf 20 -preset slow \
  -c:a aac -b:a 192k output.mp4

Best for: Offline encoding where quality matters more than file size.

Comparison of Bitrate Modes

Bitrate Recommendations by Resolution

The ideal bitrate depends on the resolution, frame rate, and codec. Here are evidence-based recommendations for each combination.

H.264 (AVC) Bitrate Recommendations

H.265 (HEVC) Bitrate Recommendations

H.265 is roughly 40-50% more efficient than H.264, so the recommended bitrates are correspondingly lower.

AV1 Bitrate Recommendations

AV1 is approximately 30-50% more efficient than H.265, pushing bitrates even lower.

For a complete codec comparison, read our in-depth guide on H.265 vs H.264 vs AV1.

Streaming vs. Download Bitrates

Streaming and download have fundamentally different bitrate requirements because of how data is delivered to the viewer.

Streaming Bitrates

Streaming video must arrive faster than it is played. If the bitrate exceeds the viewer's available bandwidth, playback stutters or drops to a lower quality level (in adaptive streaming).

Key streaming constraints:

• Must be below the viewer's available bandwidth (typically 5-100 Mbps for home internet)
• Should account for network variability (use 80% of available bandwidth as a ceiling)
• Adaptive bitrate streaming (ABR) offers multiple quality levels

Common Streaming Service Bitrates

These bitrates are lower than what you would use for a downloaded file because streaming services use highly optimized encoding (per-scene analysis, multi-pass encoding, content-adaptive settings) that extracts maximum quality from every bit.

Download Bitrates

Downloaded files do not have real-time constraints. You can use higher bitrates without worrying about buffering:

# High-quality download encode
ffmpeg -i input.mp4 -c:v libx264 -crf 18 -preset slow \
  -c:a aac -b:a 256k output.mp4

For YouTube upload bitrate recommendations, see our best video settings for YouTube guide.

Codec Efficiency: Getting More Quality per Bit

Different codecs extract different amounts of visual quality from the same bitrate. This efficiency is measured by encoding the same source at the same bitrate and comparing the visual quality.

Relative Codec Efficiency

This means that if you need 10 Mbps with H.264 to achieve a certain quality, you need only about 6.5 Mbps with H.265 or 5 Mbps with AV1 for the same visual result.

Understanding CRF Values

CRF (Constant Rate Factor) is the most popular quality control for offline encoding. Each codec has its own CRF scale.

CRF Values Across Codecs

The CRF scale is logarithmic. For H.264, increasing CRF by 6 roughly doubles the compression ratio (halves the file size). For H.265, the same effect occurs at a CRF increase of about 5.

Finding the Right CRF

# Encode a 30-second test segment at different CRF values
for crf in 18 20 22 24 26; do
  ffmpeg -i input.mp4 -ss 60 -t 30 -c:v libx264 -crf $crf \
    -preset medium -c:a copy "test_crf${crf}.mp4" -y
done

# Compare file sizes
ls -lh test_crf*.mp4

Then watch the test segments and pick the highest CRF value where you cannot notice quality degradation. This gives you the smallest possible file at your acceptable quality threshold.

Content Complexity and Bitrate

Not all video content is created equal. The complexity of the visual content dramatically affects how much bitrate is needed.

Low Complexity (Compresses Well)

• Screen recordings, presentations, and tutorials
• Talking head videos with static backgrounds
• Animation with flat colors and simple shapes
• Slow-panning landscape shots

High Complexity (Needs More Bitrate)

• Fast-motion sports and action sequences
• Scenes with rain, snow, confetti, or particles
• Dense foliage, grass, and water surfaces
• Film grain and noise (the encoder treats noise as detail)

A talking head video at CRF 23 might produce a 2 Mbps file, while an action scene at the same CRF might produce 15 Mbps. CRF automatically handles this variation, which is why it produces better results than fixed bitrate for variable-complexity content.

Denoising to Reduce Bitrate

If your source has film grain or sensor noise, removing it before encoding can significantly reduce file size without meaningful quality loss:

# Light denoising for moderate noise
ffmpeg -i input.mp4 -vf "nlmeans=6:3:7:3" \
  -c:v libx264 -crf 20 -preset slow -c:a copy output.mp4

# Aggressive denoising for very noisy footage
ffmpeg -i input.mp4 -vf "nlmeans=10:5:9:5" \
  -c:v libx264 -crf 20 -preset slow -c:a copy output.mp4

For more compression techniques, see our guide on compressing video without losing quality.

Calculating File Size from Bitrate

The formula for estimating file size is straightforward:

File Size (MB) = (Video Bitrate + Audio Bitrate) × Duration (seconds) / 8 / 1024

Where bitrate is in kbps.

Quick Reference File Size Estimates

These estimates include only the video stream. Add 1-2 MB per minute for 128-192 kbps audio.

Calculating Bitrate for a Target File Size

To work backwards from a desired file size:

Target Bitrate (kbps) = Target Size (MB) × 8 × 1024 / Duration (seconds) - Audio Bitrate

For example, to fit a 3-minute video into 50 MB with 192 kbps audio:

Target Bitrate = 50 × 8 × 1024 / 180 - 192 ≈ 2083 kbps (~2 Mbps)

Use the Video Compressor to handle these calculations automatically by setting a target file size.

Audio Bitrate: Do Not Forget the Other Half

While video typically accounts for 90-95% of file size, audio bitrate still matters.

For most video content, 128-192 kbps AAC is the sweet spot. Going higher wastes bytes that could be allocated to video quality. For more on audio quality, see our guide on audio bitrate and quality.

Checking and Analyzing Video Bitrate

Get Bitrate of an Existing File

# Quick overall bitrate
ffprobe -v error -show_entries format=bit_rate \
  -of csv=p=0 input.mp4

# Detailed stream-level bitrate
ffprobe -v error -show_entries stream=codec_name,bit_rate,width,height \
  -of table input.mp4

Analyze Bitrate Variation Over Time

# Generate per-frame bitrate data
ffprobe -v error -select_streams v:0 -show_entries \
  frame=pkt_size,pts_time -of csv input.mp4 > bitrate_data.csv

This data can be graphed to visualize how bitrate fluctuates throughout the video, revealing which scenes are bitrate-heavy and might benefit from additional compression.

Practical Bitrate Selection Guide

For platform-specific bitrate settings, see our best video settings for YouTube and social media video specs guide.

Frequently Asked Questions

Does higher bitrate always mean better quality?

No. Beyond a certain point (the "saturation point"), increasing bitrate adds file size without visible quality improvement. For 1080p H.264, this typically occurs around 15-20 Mbps. Beyond that, you are storing information the human eye cannot perceive.

What bitrate should I use for YouTube?

YouTube re-encodes everything, so upload the highest quality source you can. Use CRF 18 with H.264 for 1080p content, or CRF 16 for 4K. The exact bitrate will depend on content complexity, but this approach ensures YouTube's encoder has plenty of data to work with.

Why is my video file so large?

Likely because of high bitrate, high resolution, long duration, or an inefficient codec. Use ffprobe to check the bitrate, then use the Video Compressor to reduce file size. Switching from H.264 to H.265 can cut size by 40-50% at the same quality.

What is the difference between Mbps and MBps?

Mbps (megabits per second) measures data rate. MBps (megabytes per second) measures file transfer speed. 1 MBps = 8 Mbps. A 5 Mbps video downloads at approximately 0.625 MBps.

Can I increase bitrate to improve a low-quality video?

No. Re-encoding a low-quality video at a higher bitrate simply preserves the existing artifacts at a larger file size. You cannot add detail that was already lost. Quality can only be preserved or reduced, never increased through re-encoding.

Conclusion

Video bitrate is the fundamental parameter controlling the balance between quality and file size. Use CRF mode for offline encoding where quality consistency matters, VBR for general-purpose files, and CBR for live streaming. Choose your codec wisely — H.265 and AV1 deliver dramatically better quality per bit than H.264.

For hands-on bitrate control, the Video Converter and Video Compressor provide intuitive interfaces for adjusting quality and file size. For detailed codec selection guidance, explore our guide on H.265 vs H.264 vs AV1 and our best video settings for YouTube.

Understanding bitrate is the key to making informed decisions about video quality, file size, and delivery. With the knowledge from this guide, you can confidently choose the right settings for any video workflow.