What Is Video Bitrate? CBR, VBR and CRF Explained

Every time you export a video, upload to a platform or set up a live stream, a number appears that controls almost everything about the result: the bitrate. Set it too low and the picture turns to blocks and smears. Set it too high and your file is huge, your upload takes forever and your viewers’ players stall. Understanding bitrate is the fastest way to better-looking, smaller videos.

This guide explains what bitrate is, how it relates to resolution and codecs, the difference between CBR, VBR and CRF, and what numbers to use for common situations.

What bitrate means

Bitrate is the amount of data used to store or transmit one second of video. It is measured in bits per second:

• kbps: kilobits per second (1,000 bits per second)
• Mbps: megabits per second (1,000,000 bits per second)

A video at 5 Mbps uses 5 million bits, or 625 kilobytes, for every second of footage. Multiply by the length and you get the file size. That is the whole calculation behind our bitrate and file size calculator:

File size (MB) = bitrate (Mbps) × duration (seconds) ÷ 8

So a 10-minute video at 5 Mbps is 5 × 600 ÷ 8 = 375 MB, plus a little for audio.

Why bitrate affects quality

Raw, uncompressed 1080p video at 30 frames per second needs about 1.5 gigabits per second. Nobody streams that. Codecs such as H.264, HEVC and AV1 compress it by a factor of hundreds by throwing away information your eyes are unlikely to miss and by describing each frame in terms of what changed since the last one.

Bitrate is the budget the encoder has for that description. With a generous budget, it can keep fine details such as skin texture, grass and film grain. With a tight budget, it has to simplify: details blur, gradients show bands, and fast motion breaks into blocks.

The bitrate you need depends on three things:

1. Resolution and frame rate. More pixels and more frames per second need more bits. 4K has four times the pixels of 1080p. 60 fps has twice the frames of 30 fps, though it rarely needs twice the bitrate because consecutive frames are more similar.
2. Content complexity. A static screen recording or a talking head needs far fewer bits than a football match, a concert with flashing lights or footage with heavy film grain.
3. Codec efficiency. HEVC and AV1 achieve similar quality to H.264 at roughly 30 to 50 percent lower bitrate. See H.264 vs H.265 vs AV1.

Bitrate vs resolution

A common mistake is to think resolution alone decides quality. It does not. A 1080p video at 1 Mbps usually looks worse than a 720p video at the same 1 Mbps, because the encoder has to spread the same budget across more than twice as many pixels.

This is why streaming services drop resolution and bitrate together when your connection slows. It is also why, if you have a hard size limit, it is often better to export at a lower resolution than to squeeze a high resolution into too few bits.

CBR, VBR and CRF: the three rate control modes

Encoders offer different ways to manage the bitrate budget. This setting, called rate control, has a big impact on quality and file size.

CBR: Constant Bitrate

The encoder aims to use the same number of bits every second, regardless of what is happening in the picture.

• Good for: live streaming, where the network connection has a fixed capacity and surprises cause buffering. Platforms like Twitch and YouTube Live recommend CBR for ingest.
• Bad for: files. Simple scenes waste bits, complex scenes do not get enough, and file sizes are larger than necessary for a given quality.

VBR: Variable Bitrate

The encoder varies the bitrate with the content: more bits for complex scenes, fewer for simple ones. You set an average target and usually a maximum.

• One-pass VBR decides as it goes. Fast, but less accurate.
• Two-pass VBR analyses the whole video first, then encodes. The average lands almost exactly on target, and bits go where they matter most. The best choice when you need a specific file size.
• Good for: on-demand streaming renditions, uploads with size limits, exports for delivery.

CRF: Constant Rate Factor (quality-based)

Instead of a bitrate, you set a quality level, and the encoder uses whatever bitrate is needed to maintain it. In x264, CRF runs from 0 (lossless) to 51 (worst). Common values are 18 to 23 for H.264 and 22 to 28 for HEVC with x265, where the scale is different.

• Good for: archiving, personal exports, and anywhere quality matters more than exact size.
• Bad for: strict size or bandwidth limits, because file size is unpredictable.

Capped CRF: the streaming sweet spot

Many streaming engineers combine the last two: CRF for consistent quality, plus a maximum bitrate and buffer size (-maxrate and -bufsize in FFmpeg). Easy content comes out small, hard content is capped so it never exceeds what your ladder allows. It is a simple form of content-aware encoding.

ffmpeg -i input.mp4 -c:v libx264 -preset slow -crf 21 -maxrate 5M -bufsize 10M \
  -c:a aac -b:a 128k output.mp4

Recommended bitrates

These are sensible starting points for H.264 in streaming and upload scenarios. Adjust up for complex content, down for simple content.

For HEVC and AV1, reduce these by roughly 30 to 50 percent for similar quality.

For YouTube uploads, higher is better, because YouTube re-encodes everything. Uploading at 12 to 20 Mbps for 1080p gives its encoder more to work with. For live streaming ingest, use the platform’s recommendations, typically 4.5 to 6 Mbps for 1080p30 and 6 to 9 Mbps for 1080p60, in CBR.

Audio bitrate

Audio uses far fewer bits but still matters:

• AAC stereo: 96 kbps is acceptable for speech, 128 kbps is a good default, 160 to 192 kbps for music.
• Opus: similar quality at lower bitrates, often 64 to 128 kbps.
• Surround (5.1): 256 to 384 kbps AAC, or Dolby Digital Plus at similar rates.

Bitrate and your internet connection

Bitrate also explains streaming performance. To watch a 5 Mbps stream smoothly, your connection needs more than 5 Mbps, with headroom for other devices and fluctuations. To live stream at 6 Mbps, your upload speed should be at least 9 Mbps. Our streaming bandwidth calculator works out the numbers for any audience size, and video streaming bandwidth requirements explains them in detail.

How to check a video’s bitrate

• VLC: open the video, then Tools → Codec Information → Statistics during playback to see input bitrate.
• MediaInfo (free, Windows, Mac, Linux): shows overall and per-stream bitrate, codec, resolution and more.
• FFprobe: ffprobe -v error -show_entries format=bit_rate -of default=nw=1 input.mp4
• File properties: Windows File Explorer shows “Data rate” and “Total bitrate” under Details for many formats.
• Quick estimate: divide the file size in megabits by the length in seconds. Our bitrate calculator does it for you.

Common bitrate mistakes

• Using the same bitrate for every video. A screen recording and a sports clip need very different budgets. Use CRF or capped CRF for files.
• Choosing CBR for files. It wastes space. Save CBR for live streams.
• Starving a high resolution. If you must go low, drop the resolution too.
• Ignoring frame rate. 60 fps needs more bits than 30 fps. If you do not need smooth motion, 30 fps saves bandwidth.
• Re-encoding repeatedly. Every generation loses quality. Keep a high-quality master and encode deliverables from it.
• Confusing bits and bytes. A 50 Mbps connection downloads about 6.25 megabytes per second, not 50.

Bitrate for different kinds of content

The same resolution can need very different bitrates:

• Screen recordings and slides: very little changes between frames. 1080p often looks crisp at 1.5 to 3 Mbps with H.264.
• Talking heads and interviews: moderate. 3 to 5 Mbps at 1080p30 is usually plenty.
• Travel, vlogs and handheld footage: camera movement means every pixel changes. 5 to 8 Mbps at 1080p.
• Sports, dance, gaming and concerts: fast motion and flashing lights. 8 to 12 Mbps at 1080p60, more for 4K.
• Grainy or noisy footage: grain looks like detail to the encoder and eats bits. Denoising before encoding can cut bitrate needs substantially.

This is why quality-based encoding like CRF works so well: it adapts to each video without guesswork.

Summary

Bitrate is the data budget for each second of video. It works together with resolution, frame rate, content and codec to set quality and file size. Use CBR for live streaming, two-pass VBR when you need an exact size, and CRF or capped CRF for everything else. Start with the recommended ranges above, check the result on real screens, and adjust. When you need to hit a size, the bitrate calculator gives you the exact number, and our guide on how to compress video without losing quality shows the full process.