When you export an MP3 from Audacity, rip a CD, or open the settings of a desktop encoder, you'll usually see a choice between constant, variable and average bitrate. This guide explains what each mode actually does, how they compare in practice, and which one fits your situation. If you're still deciding on the number itself, start with our guide to MP3 bitrate.
What is bitrate, briefly?
Bitrate is how much data the encoder uses for each second of audio, measured in kilobits per second (kbps). More bits let the encoder keep more detail, and they also make the file bigger. The size of an MP3 is roughly its average bitrate multiplied by its duration, so a 4-minute song at 128 kbps is about 3.8 MB and the same song at 320 kbps is about 9.6 MB.
What CBR, VBR and ABR change is how those bits are spread across the song.
How CBR works
With constant bitrate, the encoder uses the same bitrate for every frame. A 192 kbps CBR file uses 192 kbps during a quiet intro, a solo voice and a loud, dense chorus alike.
Advantages
- Predictable size. You can calculate the file size before you encode.
- Maximum compatibility. Every MP3 player, car stereo and app plays CBR.
- Accurate seeking and duration. Because each second takes the same space, players can jump to any point and show the correct length without extra information.
- Simple for streaming and broadcast. A steady data rate is easy to plan for.
Disadvantages
- Wasted bits on simple passages. Silence and quiet parts get as many bits as complex ones.
- Possible shortfall on complex passages. At low bitrates, dense music may not get enough bits, which is where artifacts appear.
How VBR works
With variable bitrate, you choose a quality target instead of a bitrate. The encoder then decides frame by frame how many bits each part needs: more for cymbals, applause and dense mixes, fewer for silence and simple sounds.
In the widely used LAME encoder, VBR quality is set with a number from V0 (highest quality, largest files) to V9 (lowest quality, smallest files). Other programs present the same idea as a quality slider or a list of presets.
Advantages
- Better quality per megabyte. Bits go where they make an audible difference.
- Smaller files for the same perceived quality, especially on music with quiet passages or a lot of dynamic range.
Disadvantages
- Unpredictable size. You only know the size after encoding, and it varies from song to song.
- Compatibility gaps on older hardware. Some old players and car stereos showed the wrong duration or had trouble seeking in VBR files. Modern encoders add a header that tells players the real length, which solves this on current devices.
- Less convenient for streaming and editing, where a steady data rate is easier to handle.
What about ABR?
ABR (average bitrate) is a middle ground. You choose a target, such as 192 kbps, and the encoder varies the bitrate around it but keeps the average close to the target. You get some of VBR's efficiency with a file size you can roughly predict. Audacity and LAME both offer it. It's a reasonable choice when you want VBR-style quality but have a size budget.
VBR vs CBR at a glance
| CBR | VBR | ABR | |
|---|---|---|---|
| What you choose | A bitrate (e.g. 192 kbps) | A quality level (e.g. V2) | A target average bitrate |
| File size | Predictable | Varies by content | Roughly predictable |
| Quality per MB | Good | Best | Very good |
| Compatibility | Universal | Very good on modern devices | Very good on modern devices |
| Seeking and duration | Always accurate | Accurate with a proper header | Accurate with a proper header |
| Best for | Old hardware, streaming, editing, fixed sizes | Personal music libraries | Size budget with good efficiency |
Is 320 kbps CBR better than V0?
At the top end, the differences are small. 320 kbps CBR is the maximum the MP3 format allows, so every frame gets the most bits possible, including silent ones. V0 aims for the highest VBR quality and typically produces smaller files because it doesn't waste bits on simple passages.
For most listeners on most equipment, both are very hard to tell apart from the original. The practical differences are:
- Choose 320 CBR if you want the simplest, most compatible file and size doesn't matter.
- Choose V0 if you want top quality with a smaller library.
Remember that no setting can restore quality that isn't in the source. A 128 kbps file re-encoded at 320 kbps or V0 is just a bigger file with the same, or slightly worse, quality.
Which one should you use?
For a music library on your phone or computer
VBR (V0 to V2 in LAME, or "high quality" in other tools) is usually the best balance. Modern phones, computers and apps handle it without issues.
For an older car stereo or MP3 player
CBR is the safer choice. If you're not sure how old your stereo is, 192 or 256 kbps CBR will play everywhere. Our guide to ripping a CD to MP3 covers the settings for car use.
For podcasts, voice notes and spoken audio
CBR is common for podcasts because hosting platforms and players handle it predictably. For speech, a modest bitrate is usually enough.
For audio you'll edit later
CBR makes cutting and seeking simple, but it's better still to keep the original lossless file (WAV or FLAC) for editing and create the MP3 at the end. Every MP3 re-encode loses a little more detail.
When you need a specific file size
CBR, or ABR if you prefer more efficiency. With VBR you can't know the size in advance.
How to choose CBR or VBR in common tools
- Audacity: when exporting to MP3, the export options include a bitrate mode (preset, variable, average or constant) and a quality or bitrate setting.
- FFmpeg with LAME: a constant bitrate is set with an audio bitrate option such as -b:a 192k, and a VBR quality level with the -q:a option, where 0 is the highest quality.
- Music app on a Mac: in the MP3 encoder's Custom import settings, there's a checkbox to use variable bit rate encoding.
- Online converters: most, including Convertola's, offer a list of fixed bitrates, which means CBR.
What Convertola uses
The Convertola MP3 converter encodes in CBR. You choose 128, 192, 256 or 320 kbps, and the conversion runs in your browser, so your file isn't uploaded. We chose CBR because it plays on every device, from new phones to old car stereos, and because the size is predictable before you convert.
If you're converting a lossless source, such as with FLAC to MP3 or WAV to MP3, 256 or 320 kbps keeps the result very close to the original. For other options on Windows, see how to convert to MP3 on Windows, and for a broader comparison of tools, see the best MP3 converters.
Common myths
"VBR always sounds worse because the bitrate drops"
No. The bitrate drops only where the encoder decides fewer bits are enough, such as silence or simple sounds. Quality is the goal; the bitrate follows.
"CBR 320 is lossless"
No. Every MP3 is lossy. 320 kbps is the highest MP3 bitrate, but the file is still compressed and some information is gone. If you need lossless audio, use FLAC or WAV.
"Re-encoding to VBR makes a file smaller with no loss"
Re-encoding an MP3 always decodes and compresses it again, which adds a new generation of loss. If you want a smaller file, it's better to encode again from the original source.
Frequently asked questions
What's the difference between VBR and CBR?
CBR uses the same bitrate for the whole file. VBR changes the bitrate from moment to moment depending on how complex the audio is, aiming for a constant quality instead.
Is VBR better than CBR?
For quality per megabyte, usually yes. For compatibility, predictable size, streaming and editing, CBR is simpler. Both work well on modern devices.
Do car stereos play VBR MP3?
Most modern ones do. Some older units had trouble showing the duration or seeking in VBR files. If you have problems, re-encode from the original source as CBR.
Is V0 the same as 320 kbps?
No. V0 is the highest VBR quality level in LAME, and its bitrate varies with the music. 320 kbps CBR uses the maximum bitrate on every frame. Both are high quality; V0 files are usually smaller.
Does Convertola use VBR or CBR?
Convertola encodes MP3 in CBR at 128, 192, 256 or 320 kbps.
Should I use ABR?
ABR is useful when you want some of VBR's efficiency but need the file size to stay close to a target. For most people, VBR or CBR is simpler.
Sources
- Wikipedia: Variable bitrate
- Wikipedia: Constant bitrate
- MDN: Web audio codec guide
- Library of Congress: MP3 (MPEG Layer III Audio Encoding)
- FFmpeg documentation
Ready to convert? Open the Convertola MP3 converter, choose your bitrate and get a CBR MP3 that plays everywhere.
