[FFmpeg-user] Converting wma to mp3, avoiding joint stereo

Moritz Barsnick barsnick at gmx.net
Sun Apr 18 16:38:16 EEST 2021

On Sat, Apr 17, 2021 at 13:42:02 -0400, Alan Corey wrote:
> can deal with.  So I did the basic
> ffmpeg -i somefile.wma somefile.mp3
> And it works, but mpg123 tells me the file is joint stereo. It's
> quite possible the wma files are joint stereo, I don't know anything
> about them, but when I convert a flac file (to wav then mp3) I can at
> least nominally output true stereo.

ffmpeg's encoder is independent of the input, joint stereo is its

> accomplish anything but I call LAME with -m s.  Is that possible with
> ffmpeg?  How?  Do I need to get into channel mapping?

As Paul wrote:
  -joint_stereo 0
(as output option).

> Joint stereo I remember from the early days of fm stereo that had to
> also be playable on mono radios.  Better than mono but not as good as
> true stereo.

It depends on the quality of the encoder, but basically, joint stereo
means that the encoder makes use of the similarity of the two channels
to optimize bandwidth use. At the same (fixed) bitrate, you may encouter
better quality in critical sections. With modern encoders (such as
mp3lame), you shouldn't notice a difference in your stereo separation.

In other words: Just continue to use joint stereo if you can.

See also


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