Length Expanded on Each Extraction

Hi folks! I’m new to Audacity & I’ve been using this software to compress my recordings for the past 2 months.

Just recently, I noticed that whenever I tried to edit the bitrate of my recording, despite being properly trimmed, the exported file expanded a tiny bit from the original file.

In the attached picture, I tried to recreate the issue where I simply exported the original file to the downgraded version & yet it still expanded (again, even only for 120-280 milliseconds).

The expansions occurred on both ends (front and rear of the exported file). Is there even any point in performing precision trimming if Audacity expanded the outcome?

This has caused me a bit of confusion; like is there something wrong with my Audacity configuration? or is it the standard/common finding in this software? How to avoid this and achieve a consistent file with no time expansions.

any clues will be highly appreciated! Thank you in advance :unamused:
Audio Expansion.png

I assume that you are exporting to MP3?

This a characteristic of MP3 compression… [u]LAME FAQ[/u]

It shouldn’t happen with WAV (uncompressed) or FLAC (lossless compression). It MAY not happen with M4A/AAC, but this is also lossy compression so it’s also “imperfect”.

aye, my aim is to reduce the .mp3 files from 320kbps to 128kbps (from lossy to lossy format) & if it’s the characteristic of such a compression mechanism, I guess there’s nothing I can do here :frowning:

I found that the same padding occurred when I tried to export the track into M4A (AAC) format, but strangely enough not with OGG Vorbis format (since in some articles, it’s said that OGG allows for gapless audio).

I also noticed that the OGG file (exported from Audacity) keeps resulting in 1411kbs in Windows explorer detail, regardless of my quality setting (from 0-10); is this a known glitch?

Yes, the Ogg Vorbis format allows gapless playback. It also, (unlike MP3), has well defined metadata support so that “tags” are the same for all platforms, regardless of which audio player is used.

Probably a Windows bug. Windows support for open formats has always been poor.

Yeah, that looks like a Windows bug… I’m seeing the same 4411kbps* with an OGG created with [u]Kabuu Audio Converter[/u].

You can check the true bitrate with [u]MediaInfoOnline[/u] (or you can download MediaInfo to your computer).

Or, since kbps is kilo_bits_ per second, and there are 8-bits in a byte, you can divide by 8 to get the file size in kilo_bytes_ per second, or you can calculate the bitrate from the file size and playing time. Just be aware that any embedded artwork makes the file bigger without affecting bitrate so that throws-off the calculation.

BTW - If you are just converting files without editing, Kabuu Audio Converter (or similar applications) are easier to use and you can convert a batch of files at once. But if you want to edit-out that original MP3 gaps you’ll need an audio editor.


  • 4411 is the bitrate for uncompressed “CD quality audio”… 44.1Khz x 16-bits x 2-channels = 1411.