I would like to convert a DVD movie audio track (the originial audio is AC3 5.1 384Kbit/sec) into stereo using oggenc -q1 quality setting. Is it a very bad idea or I should choose a higher quality setting like -q3? Note that the converted audio will be heard on low cost acoustics.

:-( I cannot edit the subject of the message.

I think you mean ac3 instead of aac?

Personally I use -q0 for the exact same purpose and I am satisfied with it. So IMO not a bad idea at all.

here is what I do:

downmix the 5.1 to stereo (NOT surround2, vorbis has issues with it)

encode with -q 0 --advanced-encode-option lowpass_frequency=999

(adjust the lowpass and other advanced options at your own discression)

edit: typo

Thank you for your advice. What does "--advance-encode-option lowpass_frequency=999" option do exactly? Does it cut frequencies below 999Hz or what?

What kind of issues?

Also, IIRC the lowpass_frequency option accepts parameters in kHz, and that would make using your value of "999" nonsense.

I would stick with a -q 6 whether the mix is stereo or multichannel. Vorbis doesn't have the proper channel coupling right now for multichannel mixes, although this is a top priority that will eventually get sorted out.

it overrides the default lowpass... and that would move the lowpass to the max (effectively off at 999khz)


issues with rear channels, tinny flanging nastyness, especially if its people talking, and was there even at -q 4.. in most cases I am unable to hear much of a difference between surround2 and stereo when encoded to vorbis at -q 0... but this 'issue' may also be because i didnt use any lowpass on the surround information (i'm actually trying headac3he's surround lowpass thing now)

... sure 999 is excessive... 24 is enough to make the lowpass efectively off when the sample rate is 48khz

On second thought, why the hell would you need to downmix it? are you telling me there is no a PCM stereo mix already on that disc that you can encode from? If this is a DVD Movie disc I am pretty confident there are two seperate mixes one AC3 5.1 mix and another PCM stereo one. Some movies are mixed better when it comes to 5.1 also. With a lot of other movies I often wonder why they even bother creating 5.1 mixes for them.

He is encoding to stereo, so channel coupling has nothing to do with this. And q6 is way to high, q3 or q4 should be just fine. Hell, you probably wouldn't hear the difference with a lower settings either.


Disabling the lowpass at those bitrates is absolutely insane, and just proves that you have no idea what you are talking about. Oh and btw, it's "--advanced-encode-option". At least make sure you type it correctly, when you make your 1337 recommendations, so that it actually works for people.


Aha, so it doesn't have issues with Surround 2, but rather with your "expert" settings. May I remind you of our beloved TOS #8 again?


Erm, PCM stereo tracks on movie DVDs are very rare. Actually, I'm pretty sure I personally have never seen such a disc.

I have one DVD that has a LPCM stereo track at 48 kHz (also the only audio track on that DVD), but it's quite rare yes. A LPCM stereo track takes up more than 3 times the space of a 5.1 AC3 track.

Sometimes there is also a 2ch AC3 track, but I wouldn't know which would be better to use as source. At settings below q2 it will probably get hard to state a preference.

..comments on q 6 below.
oops, I've edited my post to correct that
to everyone their own (opinion)

basically nonsense, but 999.0000 is as high as the lowpass goes for oggenc, even at -q 10.... but enough of lowpass talk......

let's not be to hasty... allow me to further explain.. When I first heard the problem, the very first thing I tried was to encode without my custom settings. Starting at q 0 and increasing the quality setting (using the default lowpass)... I was still able to hear the flanginess (although barely) at q 4. At q 6 I could not. (my initial though on this was the lossy stereo, it was said that at q6 only lossless stereo coupling was used.. I hear this isn't the case with aotuv)... so I second HotshotGG's recomendation of q 6, but only if downmixing to prologic(II). I can not provide abx tests to prove that I could hear this problem, it was quite some time ago (using vorbis 1.0.1) and I no longer have this problem file. (it was the evangelion movie death and rebirth, the very beginning sequence)... I am merely sharing my experience here as a caution for others when encoding downmixed (surround(2)) audio to vorbis.. and is the reason why I personally downmix to stereo instead.

it's proven fact. Vorbis was specifically designed that way for concerned "audiophiles" who didn't want the stereo image quantized, because they would loose sleep at night above -q 6 that is. The mapping specification in the code is their and John33 fixed it for Vorbis decoding I compliance stream, but the coupling routines for more than one submap aren't there. It would be a real pain in the behind to write them too. The lowpass is ok in some circumstance, don't play around with it all of the time though.



I prefer LPCM mixes. A few of my DVD's have them I believe. LPCM mixes or lossless should be used on DVD-A mixes anyway. It's better that way. It's not like they don't have the space, despite the fact we are discussing DVD-V.