[MPlayer-dev-eng] New audio and mixer interface, and old audio plugins

[D Richard Felker III]

On Sat, Jan 18, 2003 at 03:33:32PM +0800, Anders Johansson wrote:
> Hi,
> 
> > > Hi,
> > > 
> > > I have started to remove the old audio plugins in my tree, found it a
> > > bit tricky because of the dependencies with the GUI. I guess I need to
> > > write the new interface before the old one is removed.
> > > 
> > > I started with the volume control, and found that there needs to be
> > > some sort of reporting of the audio capabilities for the whole thing
> > 
> > BTW, can we make the default volume scaling 0dB (no change) instead of
> > the current -10? I can't se how it's possibly useful to do -10 by
> > default since 90% of movies already have their sound inaudibly soft
> > anyway...
> 
> This is a safety setting to make sure the user doesn't blow up his
> stereo, to override use -af volume=0

This is nonsense! If "mplayer -af volume=0 file" would blow up the
stereo, so would just plain "mplayer file"!!! Arrg! This is as silly
as making -50 contrast the default for -vop eq because you're worried
that someone might get seizures from bright high contrast flashing.
This default is annoying and unusable; it's just there as a 'safety'
feature.

Anyone who has their stereo set up so that the max output of the sound
card can damage it is just asking for trouble...

> > Also I have some ideas for speeding up the volume filter a lot and
> > supporting more features like soft clipping in the integer code. Is it
> > ok to commit stuff to libaf or do you want to take care of all the
> > changes for now?
> 
> I don't care much about integer processing, commit anything you want
> as long as it doesn't brake anything else. If you plan to do any
> changes to float stuff, then my only concern is that the dynamic range
> shouldn't be affected, i.e look out for conversions and floating point
> underflow, and stick to float not double.

Hmm, the float code is very slow too, so maybe I'll try to improve it
too for people who want to use it. Does it actually work now?

> > > to work nicely. When I dug around I also found an audio input
> > > interface is starting to be built up. IMHO we should have one
> > > interface to the audio that supports both input and output for
> > > multiple audio devices (like audio out to two sound-cards, a network
> > > connection and file at the same time).
> > 
> > How does this work when the cards don't have a common clock source?
> > Will mplayer use one as a master clock source while the filter layer
> > controls the other and dynamically warps audio?
> 
> One (or the rtc) device is used for the time base, and resampling is
> used for compensation. The resample rate is adaptive, so if the clocks
> drift the resample rate changes (as long as the changes are below 1Hz
> it is not possible to hear). It will be a SRLL (Sample Rate Locked
> Loop :)

:)

> > IMHO -af should force a specific chain of filters to be loaded, just
> > like -vop does for video; if there's going to be some sort of config
> > for filter order preference on dynamic insertion, it should be
> > separate. Or, perhaps you could just have all the filters in -af but
> > have controls to turn them on/off?
> 
> I am talking about dynamic filter insertion and removal, i.e through
> the user interface during playback.
> 
> > One other idea, and this could apply to video filters too... It'd be
> > nice to have a way of specifying default filters that always get used,
> > in addition to ones specified on the command line. For example I
> > imagine dxr3 users always want -vop lavc at the end of their chain,
> > and users with yv12-impaired cards might always want -vop yuy2 at the
> > end. Similarly someone might always want to have the surround filter
> > loaded, and not have to manually specify it every time when using
> > other filters on the commandline.
> 
> What do you mean? The surround filter gets unloaded automatically if
> it isn't needed, you can have it enabled always.

Right. But suppose I put af=surround in my .mplayer/config, then I use
a command like mplayer -af volume foo.avi. Surround won't get loaded
unless I manually do -af volume,surround, and I'm likely to forget
this if surround is normally auto-loaded by my config file.

> > > Also is it desirable to be able to instancify multiple mixers?
> > 
> > IMHO yes, all filter modules should be reentrant and support multiple
> > instances.
> 
> Sorry, perhaps I wasn't very clear. I mean the mixer found in mixer.c,
> thats where I will write the runtime interface to the audio filter
> layer. It will sort of look (in terms of functionality) like the
> interface found on a combined D/A and amplifier that are used along
> with stand alone DVD players. Is it desirable to perhaps create
> different interfaces to the audio filter layer and have them
> dynamically loadable, or is it overkill, that is my question? This
> will be applicable to mencoder as well where one perhaps will want one
> mixer for each audio stream.

Hmm... IMHO mixer.c is sort of irrelevant to mencoder; you wouldn't
need to be adjusting settings interactively during the movie, just
with initial config to the audio filters on the command line. But
perhaps there's something I don't understand that makes it useful. I'd
see what Arpi has to say on this matter.

Rich