| -m mode
mode = s, j, f, d, m
Joint-stereo is the default mode for stereo files with VBR when -V is more than 4 or fixed
bitrates of 160kbs or less. At higher fixed bitrates or higher VBR settings, the default is
stereo.
(s)imple stereo
In this mode, the encoder makes no use of potentially existing correlations between the two input
channels. It can, however, negotiate the bit demand between both channel, i.e. give one channel
more bits if the other contains silence or needs less bits because of a lower complexity.
(j)oint stereo
In this mode, the encoder will make use of a correlation between both channels. The signal will
be matrixed into a sum ("mid"), computed by L+R, and difference ("side") signal, computed by L-R,
and more bits are allocated to the mid channel. This will effectively increase the bandwidth if
the signal does not have too much stereo separation, thus giving a significant gain in encoding
quality.
Using mid/side stereo inappropriately can result in audible compression artifacts. To much
switching between mid/side and regular stereo can also sound bad. To determine when to switch to
mid/side stereo, LAME uses a much more sophisticated algorithm than that described in the ISO doc‐
umentation, and thus is safe to use in joint stereo mode.
(f)orced MS stereo
This mode will force MS stereo on all frames. It is slightly faster than joint stereo, but it
should be used only if you are sure that every frame of the input file has very little stereo sep‐
aration.
(d)ual mono
In this mode, the 2 channels will be totally independently encoded. Each channel will have
exactly half of the bitrate. This mode is designed for applications like dual languages encoding
(for example: English in one channel and French in the other). Using this encoding mode for regu‐
lar stereo files will result in a lower quality encoding.
(m)ono
The input will be encoded as a mono signal. If it was a stereo signal, it will be downsampled to
mono. The downmix is calculated as the sum of the left and right channel, attenuated by 6 dB.
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