[MPlayer-users] playing two audio streams at the same time

[Nicolas George]

Le decadi 20 ventôse, an CCXXI, Peter Münster a écrit :
> If you have a VDR-recording or a DVD-image with several audio channels,
> is it possible with mplayer, to send one audio channel (German) to the
> headphones and the other audio channel (French) to the speakers (or
> another headphones)?
> 
> If it's possible, what version do I need at least and what must be
> configured?

This is not currently possible with MPlayer.

> If not, what would be the effort for a developer to implement such a
> feature (in hours, $, € or whatever)?
> 
> Or do you know other software for watching DVDs and VDR-recordings, with
> such a feature?

There is two aspects to your question.

The first is very obvious: is your hardware capable of playing two different
streams on the two outputs (headphones and speakers)? On some hardware,
plugging the headphones will mute the speakers; on some other hardware, you
can disable the muting, but they will play the same.

If your hardware is capable, then a software solution can be found.

The easiest situation would probably be if your speakers and headphones are
plugged to the same sound controller as different channels. For example, I
myself use a motherboard with 7.1 output but only have 5.1 speakers, and I
plugged my headphones where the side speakers should go.

If this is your situation, then there is an easy workaround: using (for
example) ffmpeg and the amerge and pan filters, extract the two audio
streams you are interested in and combine them into a layout suitable for
your setup. For example, on my setup, I would have to produce a 7.1 file
with French on front left and front right, the same on rear left and rear
right, silence on front center and subwoofer¹, German on side left and
right.

Then you just have to use the -audiofile option of MPlayer to use that file
as the audio stream.

This is very similar to the solution used by analog TV to broadcast programs
in both original and dubbed versions.

If the headphones and speakers are not physically on the same controller,
then you have to find another solution.

ALSA has a plugin to bind several audio streams and make them appear as a
single output device:
http://www.alsa-project.org/alsa-doc/alsa-lib/pcm_plugins.html#pcm_plugins_multi
But it may not work correctly if the sound controllers have a slightly
different time base.

Another solution would be to use network synchronized playback:
http://www.mplayerhq.hu/DOCS/HTML/en/networksync.html


1: I can not understand how people who design upmixing software thing it is
a good idea to ruin the stereo by mixing left and right into center.


Regards,

-- 
  Nicolas George
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