[MPlayer-dev-eng] [PATCH] Proof of concept extrasurround plugin

[Anders Johansson]

Hi,

> Hi,
> 
> This is an _experimental_ patch. Only a proof of concept.
> Use it at your own risk!
> 
> The problem: Most video files come with stereo or dolby surround 
> audio encoding.
> These files doesn't sound very well on a 5.1 speaker set. The purpose of
> this plugin is to address this problem.
> 
> The solution (well, workaround :-) ): Take the surround plugin, 
> and make it output to the 6th (subwoofer) channel too. 
> The 5th (center speaker) channel remains silent, because it would ruin 
> the stereo experience.
> The signal sent to the subwoofer channel is a mono mix of the two front
> speakers filtered through a lowpass filter.
> This plugin is only suitable for people with a 5.1 soundcard!
> 
> The current implementation:
> The current implementation is not suited for CVS commit. But it works for
> me. 
> 
> TODO: 
> -Make the new functionality an option of the plugin
> -Use the same lowpass filter as in the original surround part of the plugin. I
> couldn't figure the firfilter thingie out, so I stole^H^H^H^H^H reused
> the simple RC lowpass filter from sox.
> -Fix the bugs

Try using my lowpass filter you find it in libao2/fir.h. It is
assembly optimized and quite easy to use. Have you read the specs of
how steep and how long the filter should be? Guess you will find them
in the dolby surround specifications. According to Steve Davies who
wrote the plugin the filter needs to be quite long to sound well. I
will be happy to help you out with using the FIR filter. We could
replace the other filters in this plugin as well while we are at it.

> KNOWN BUGS:
> -I couldn't play any files with 48000 Hz sample rate. 
This is might be the upsampling bug that I haven't been able to
fix. What did it sound like?

[snip]

> Thanks,
> kisg

We might want to use this even if there is no surround sound
information just to generate the necessary sub-woofer channel. That
would make the sound a lot better on cheap surround sound systems,
where the front L and R speakers are small.

Cheers,
//Anders