[Vorbis] bitrate limits don't work with -q settings?

[Sander Sweers]

Here are some more tests i did with various combinations.

oggenc -q 3 sinewave.flac -> Average bitrate: 69.1 kb/s
oggenc -m 96 sinewave.flac -> Average bitrate: 96.9 kb/s
oggenc -m 96 -q3 sinewave.flac -> Average bitrate: 69.1 kb/s
oggenc -q 3 -m 360 sinewave.flac -> Average bitrate: 69.1 kb/s
oggenc -m 96 -M 360 sinewave.flac ->  Average bitrate: 130.6 kb/s
oggenc -q 3 -m 96 -M 360 sinewave.flac -> Average bitrate: 0.7 kb/s
oggenc -q 3 -m 360 -M 360 sinewave.flac -> Average bitrate: 0.7 kb/s

The last ones are really weird? The file ony has one tick at the
beginning an after that silence.

The issue however is when using a -q3 together with a -m 96 oggenc
kind of ignores the -m 96. Is this normal?

Sander

On Wed, 29 Dec 2004 23:11:45 -0500, Nic Watson <nic at ghs.com> wrote:
> I just tried it on my Debian box; I see the same thing as on my Windows
> box.  I noticed that -q3 will dip below 96 kbps on only about 5% of my
> collection.  Some files have more entropy than others.
> 
> For example, try to encode this file:
> 
> <http://www.accalia.org/sinewave.flac>
> 
> It is 30 seconds of sine wave in stereo, a highly compressible file.
> 
> You'll see that the average bitrate falls well below the -m setting.
> 
> An intersting side note is that in trying to come up with a small test
> file that I could distribute, I took 3 differenct 30-second segments
> from input.wav, my original test case.  All encoded > 96 kbps.  Perhaps
> there is something peculiar about the bitrate management when encoding
> certain files.
> 
> Nic
> 
> Sander Sweers wrote:
> 
> > Well, I can not reproduce this behaviour in Linux.
> >
> > I am using oggenc "OggEnc v1.0.1 (libvorbis 1.0.1)"
> >
> > oggenc -q3 03.\ Unknown\ Quantity.flac
> >
> > Opening with flac module: FLAC file reader
> > Encoding "03. Unknown Quantity.flac" to "03. Unknown Quantity.ogg" at
> > quality 3.00
> >         [ 99.7%] [ 0m00s remaining] \
> >
> > Done encoding file "03. Unknown Quantity.ogg"
> >
> >         File length:  4m 37.0s
> >         Elapsed time: 0m 34.5s
> >         Rate:         8.0478
> >         Average bitrate: 126.4 kb/s
> >
> > -----------------------------------------------
> > oggenc -q3 -m 96 03.\ Unknown\  Quantity.flac
> >
> > Enabling bitrate management engine
> > Opening with flac module: FLAC file reader
> > Encoding "03. Unknown Quantity.flac" to "03. Unknown Quantity.ogg" at
> > quality level 3.00 using constrained VBR (min 96 kbps, no max)
> >         [ 99.7%] [ 0m00s remaining] \
> >
> > Done encoding file "03. Unknown Quantity.ogg"
> >
> >         File length:  4m 37.0s
> >         Elapsed time: 1m 35.5s
> >         Rate:         2.9087
> >         Average bitrate: 126.4 kb/s
> >
> > For me the bitrate does not drop under 96kbit when using -q3. I have
> > not  experienced any problems with my iriver H120 yet.
> >
> > Maybe you should move to Linux ;-) Seriously though, get the official
> > binary encoder from the Xiph site and see if this problem still
> > exists.
> >
> > I did however see a drop in performance when limiting the minimum
> > bitrate to 96k. Is this because of the different engine being used?
> >
> > Sander
> >
> >
> > On Wed, 29 Dec 2004 14:25:43 -0500, Nic Watson <nic at ghs.com> wrote:
> >
> >>Thanks for the quick response.  To get versioning out of the way, I
> >>recompiled the libraries and oggenc from mainline svn yesterday night.
> >>I see the same results.
> >>
> >>Unfortunately, I am stuck on a stupid transport.  On the IRiver players,
> >>any time the bitrate dips below 96kbps, you'll hear a click or pop, and
> >>the song will usually end.  -q3 -m 96 doesn't work.  Is there any way to
> >>use VBR and absolutely guarantee that the bitrate won't fall below a
> >>certain level?  I figured that's what the bitrate_hard_min option was
> >>for, but it seems to have the opposite effect.
> >>
> >>Nic
> >>
> >>Ralph Giles wrote:
> >>
> >>
> >>>On Tue, Dec 28, 2004 at 10:23:50PM -0500, Nic Watson wrote:
> >>>
> >>>
> >>>
> >>>>The problem I'm seeing is that oggenc's VBR encoding doesn't seem to pay
> >>>>attention to any sort of bitrate limitation, either the -m or
> >>>>bitrate_hard_min settings.  It isn't that it temporarily dips below the
> >>>>minimum; the average for the whole (in this case, easily compressible)
> >>>>file is 10-20% too low.
> >>>
> >>>
> >>>Are you complaining that the encoder does too good a job? :-)
> >>>
> >>>The managed bitrate modes use a different engine from the standard
> >>>constant-quality engine, and is mutually exclusive with -q. You have
> >>>to turn it on with -b or in more recent versions of oggenc with
> >>>--managed.
> >>>
> >>>
> >>>
> >>>>I see roughly the same results on an old 1.0.1 version of oggenc as well
> >>>>as a new vorbis 1.1-linked one I found on rarewares.org.
> >>>
> >>>
> >>>The managed bitrate handling was changed in the 1.1 release; I don't
> >>>know if the rarewares oggenc is the updated version from svn or not, so
> >>>it may be using the same logic as the 1.0.1 version.
> >>>
> >>>If it's underruns you're worried about you probably shouldn't be using a
> >>>managed mode; -q will do a better job. You really only need this if
> >>>you're on some stupid transport that really can't handle the normal vbr
> >>>streams.
> >>>
> >>> -r
> >>>
> >>
> >>_______________________________________________
> >>Vorbis mailing list
> >>Vorbis at xiph.org
> >>http://lists.xiph.org/mailman/listinfo/vorbis
> >>
> >
> >
> >
> 


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