M4A exported at incorrect bitrate


I’m using Windows 10 Pro 21H2, Audacity 3.1.3, and FFmpeg for Audacity 2.2.2.

I’m also using MP3tag 3.11 to check the bitrate of M4A files.

If I open a 128-bit M4A file in Audacity and export it as M4A, setting Quality to 128-bit, the file size increases from 118MB to 276MB, and MP3tag reports that the output file bitrate is 308 kbit/sec.

I downloaded “regular” FFmpeg 5.1.1-essentials_build-www.gyan.dev and used this command to convert the output file back to 128-bit:

ffmpeg -i “D:\FromAudacity.308.m4a” -b:a 128k “D:\new.128.m4a”

MP3tag confirms that it’s 128 kbit/sec. The file size is down to 115MB.

So I’ve got what I need, but thought I should let someone know that the M4A bitrate setting doesn’t seem to work! Or am I missing some setting to get it to work?


Thanks for reporting it. It’s already logged as a bug: https://github.com/audacity/audacity/issues/1818

Thanks very much. Glad to see that it’s slated to be address in version 3.2:


I sadly suspect that this means one if the future 3.2.x and not the upcoming 3.2.0 scheduled for next week. :unamused:


I sadly suspect that this means one if the future 3.2.x and > not > the upcoming 3.2.0 scheduled for next week. > :unamused: >

Fortunately it’s not something I need often.

Regardless, I also want to give at shout out to @steve who kindly let me know that the bug has been reported and provided a link, even though it’s probably reported in previous threads here. Audacity is one of maybe 20 programs I use every week, so I’m not steeped in the current details. Steve (and probably many others here) do a great service by keeping up with the product and especially by acting as an interface between the forum and Github. I can’t tell you how many times I have been dissuaded from reporting a problem because it means filing a bug report or contacting support. Can I do it? Yes. Is it worth an hour or two of my time to carefully duplicate, document, find the right repository, learn the reporting rules, etc.? Rarely. I love it when super-users generously share their knowledge and act as a super-index, recalling what’s been reported where and spreading that knowledge around. Thanks!