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

[Alan Corey]

Right,  FM mono (since FM stereo came out) is L+R, then if you can
manage stereo reception the second channel is L-R.  I set up a car
stereo once with 8 switches, you could switch each (of 4) speakers
from left to right, you could also flip the phase of each.
Interesting experiment but I quickly found my favorite and left it
that way.  Something like front LR but rear RL I think.

MPEG 1.0 L III vbr 44100 stereo
mpg123 no longer says joint stereo, so I'll change my batch scripts
and re-run my conversions.  I just listened to a fixed piano piece
(with headphones) that must have had 2 mics on the piano, one at the
bass end and one at the treble.  Classical, think 2 mics in an open
grand piano.

Thank you.


On 4/18/21, Moritz Barsnick <barsnick at gmx.net> wrote:
> 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
> default.
>
>> 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
> https://wiki.hydrogenaud.io/index.php?title=Joint_stereo#Additional_information
>
> Cheers,
> Moritz
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