[MPlayer-users] 3-pass encodes with ogg vorbis?

[*]

--- D Richard Felker III <dalias at aerifal.cx> wrote:
> On Mon, Jan 19, 2004 at 09:54:54PM -0800, * wrote:
> > --- D Richard Felker III <dalias at aerifal.cx> wrote:
> > > On Mon, Jan 19, 2004 at 06:09:20PM +0000, Goran Hane wrote:
> > > > Just a thought, but why don't use normalize for audio-normalization,
> just
> > > > run normalize audiodump.wav after the audio is extracted and then
> oggenc
> > > > it?
> > > 
> > > NEVER blindly normalize audio. It will hurt quality severely if your
> > > samples frequently go near +-32767, since frequency-space codecs
> > > cannot reliably reproduce these values without clipping. If your
> > > normalization program is smart enough to keep the peak sufficiently
> > > below the limit, it's probably ok, but you should do double-blind
> > > listening tests to confirm that the quality isn't reduced. IMO it's
> > > MUCH safer to adjust volume at playback time rather than during
> > > encoding. With ogg/vorbis you can even insert a tag in the file header
> > > to automatically amplify the output.
> > > 
> > > Rich
> > > 
> > I don't understand how adjusting at playback would be any different
> > than during encoding, unless the idea is that is changeable.
> 
> That's because you don't understand DCT. Get a math/engineering text.
> :)
> 
Okay!  First I'll get a dictionary to find out what DCT is.

> > Also I should mention, that I think transcode uses a linear rescale
> > (or that's what it sounds like anyway) and mencoder seems to use dB,
> > so I've been converting with:
> > 
> >     mencoder rescale = 20*log(transcode suggested volume rescale)
> 
> 20?? Where did you get that number? It will definitely clip the audio,
> ruining quality. 10 is the correct number for your formula.
> 
I thought 20*log was for supposed to be for amplitudes and 10*log
was for power?  I see there are both in libaf/af_volume.c:

case AF_CONTROL_VOLUME_LEVEL | AF_CONTROL_GET:
  return af_to_dB(AF_NCH,s->level,(float*)arg,20.0);
case AF_CONTROL_VOLUME_PROBE | AF_CONTROL_GET:
  return af_to_dB(AF_NCH,s->pow,(float*)arg,10.0);

I guess I used the wrong one.

> Again, NEVER try to normalize audio before encoding unless you FULLY
> UNDERSTAND EXACTLY what it involves.
> 
> Rich
> 
But it would probably be a long time before I would fully understand
that.  And some DVDs are so abnormally quiet that I just can't help
myself.

Anyway I'm glad I asked.  I guess I'll have to redo the 10 or so
DVDs I've already done at some point, maybe when H.264 comes out.
Thanks!



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