What is video bitrate and why does it matter?

When people talk about video quality, they often land on “bitrate.” It’s one of those terms that sounds more complicated than it is.

What is bitrate?

Bitrate is the amount of data used per second of video, measured in kilobits per second (kbps) or megabits per second (Mbps).

Higher bitrate = more data per second = better quality and larger file size. That’s the whole trade-off.

Video bitrate vs audio bitrate

A video file has two separate bitrates:

• Video bitrate controls image quality. Typically 1,000–50,000+ kbps depending on resolution and quality settings.
• Audio bitrate controls sound quality. Usually 96–320 kbps. Much less significant for file size.

When people refer to “bitrate” without qualification, they mean video bitrate.

Typical bitrate ranges

CBR vs VBR

Constant Bitrate (CBR) uses the same bitrate throughout the video regardless of scene complexity. Simple scenes waste bits; complex scenes get no extra budget. CBR is mainly used for live streaming where the receiver can’t buffer.

Variable Bitrate (VBR) allocates more bits to complex scenes and fewer to simple ones. The result is better quality at the same average file size. Modern encoders like FFmpeg use VBR by default.

CRF encoding (used by smaller.video) is a form of VBR that targets a constant quality level rather than a constant bitrate. It’s generally the best approach for offline compression.

How bitrate relates to CRF

When you set CRF in H.264 encoding, you are not setting a bitrate directly. You’re telling the encoder: “maintain this quality level, and use whatever bitrate is needed.” On a talking-head video with a plain background, that might be 1,000 kbps. On a fast-action sports clip, it might be 10,000 kbps at the same CRF value.

This is why CRF is preferred for most compression: you set the quality you want, and the encoder figures out the bitrate.

Choosing the right approach

CRF encoding is the right default. Set the quality target (CRF 18–28) and let the encoder handle bitrate. You get the best quality-per-bit ratio.

Target bitrate is useful when you have a strict file size requirement (email attachment limits, for example). Calculate: target_bitrate_kbps × duration_seconds / 8 / 1024 = file_size_MB.

CBR is only worth using for live streaming.

Practical example

You have a 10-minute video and need it under 100MB for email:

Target: 100MB
Duration: 600 seconds
Budget: 100 × 1024 × 8 / 600 = ~1365 kbps total
Subtract audio (128 kbps): ~1237 kbps for video

Set that as your target video bitrate with -b:v 1237k, or use CRF 26–28 which will likely land near that automatically.

For most cases, the quality slider in smaller.video handles this — you pick how much to compress, and the tool calculates a target bitrate from your file’s duration and size.