[MPlayer-dev-eng] [PATCH] fix for -srate bug

[D Richard Felker III]

On Thu, Oct 21, 2004 at 01:08:41PM -0400, Giacomo Comes wrote:
> On Thu, Oct 21, 2004 at 10:55:51AM -0400, D Richard Felker III wrote:
> > On Thu, Oct 21, 2004 at 01:22:20PM +0200, Diego Biurrun wrote:
> > > D Richard Felker III writes:
> > > > On Tue, Oct 19, 2004 at 01:37:02AM +0200, Diego Biurrun wrote:
> > > > > Giacomo Comes writes:
> > > > > > 
> > > > > > This should go in the documentation, or mencoder should be fixed and be able to use
> > > > > > -af resample without -srate.
> > > > > 
> > > > > What is the problem, -af should work with MEncoder.
> > > > 
> > > > it doesn't. when the broken af was first committed it was designed for
> > > > the output end to be overridden by the negotiated parameters between
> > > > the codec and the ao driver. mplayer was fixed but mencoder never was.
> > > > so even if you specify resample, mencoder will reconfigure your
> > > > resample filter to resample to the original rate... :(
> > > 
> > > OK, let me try to distill this into documentation.  Currently in the
> > > man page we have
> > > 
> > > resample[=srate[:sloppy][:type]]
> > >   Changes the sample rate of the audio stream to an integer srate in Hz.
> > >   It only supports the 16-bit little-endian format.
> > > 
> > > IIUC I would just have to mark this MPlayer only, right?  Like so:
> > 
> > no. it's not mplayer-only!! it works with either, but you must
> > force-override the output samplerate to keep mencoder from undoing
> > your filter chain. so, something like:
> > 
> > -af resample=44100:0:0 -srate 44100
> 
> Is this really true?
> I'm not sure. I did this test:
> (source.asf has 8000Hz audio)

probably mono too.. or 8bit?

> 1) mplayer source.asf -af resample=44100:0:0 (audio has distortion)
> 2) mplayer source.asf -af resample=44100:0:1 (audio ok)
> 3) mplayer source.asf -af resample=44100:0:2 (audio has noise)
> 
> mencoder source.asf -ovc lavc -oac lavc -srate 44100 -frames 150 -af resample=44100:0:0
> (the output is test.avi and has mp2 audio)
> test.avi has distortion as in 1)
> 
> mencoder source.asf -ovc lavc -oac lavc -srate 44100 -frames 150 -af resample=44100:0:1
> test.avi is ok as in 2)
> 
> mencoder source.asf -ovc lavc -oac lavc -srate 44100 -frames 150 -af resample=44100:0:2
> test.avi is ok as in 2) but the volume is higher
> (this is different from what expected)
> 
> So, may be resample works (with -srate) for mencoder too, but at least in one case
> it works differently (bug?).

mode 2 (float) resample is ALWAYS broken for me (produces white noise)
so i have no idea...

> > adding -af-adv force=3 (disable) couldn't hurt either..
> 
> No. It does hurt. With:
> 
> mencoder source.asf -ovc lavc -oac lavc -srate 44100 -frames 150 -af resample=44100:0:n -af-adv force=m
> 
> if m=0,1,2 the -af-adv option doesn't do anything. 
> It is the n in resample that select the resample algorithm.
> 
> if m=3 and n=0,1 then the audio in test.avi goes at double speed. 
> I need to play it with -speed 0.5 in order to listen a 
> normal speed sound.
> if m=3 and n=2 then in test.avi there is ONLY noise.
> 
> Conclusion:
> with mencoder you can use
> 	-srate AND (-af resample XOR -af-adv force)

no, you need to explain better what you're doing. most likely more
filters are needed (which would be autoloaded if you didn't force them
off) and so you need to load the right filters manually. there are
many possible conditions so i can only guess...

rich