48 kbps AAC Encoders Test - Q1 2006 Edition Options

[dimzon]

Why discarding VBR and using 48 kbps at the same time?

Please, use both modes CBR/VBR if possible!

[Shade[ST]]

If someone can stream 48 kbps (i.e. if he doesn't have a dial-up), then he should be able to handle VBR without problem. No?

Streaming 48kbps on dial-up IS possible.

[IgorC]

Somebody want test at 32 kbps , another at 64 and higher. Also many people want at 48 kbit/s.   It´s difficult to establish an average bitrate  to satisfy all users.
48 kbit/s is an average  bitrate ... maybe most wanted. I know teh results  can be different for 32-48-64-.... bitrates. Or maybe let´s vote (making poll)?

I have nothing against 48 kbps; I'm not in favor of 32 or 64 kbps instead. But I'm just looking for coherence. Why discarding VBR and using 48 kbps at the same time? If someone can stream 48 kbps (i.e. if he doesn't have a dial-up), then he should be able to handle VBR without problem. No?

I dont mind about VBR. But it less predictable for final size. In consequence less fair. Maybe ABR will be good.

[dimzon]

Finally somebody understand me and other people like me, Dimzon  froom D9...

Yeah! AAC+ is perfect choice for soundtrack:
H264 + HE-AAC =MP4 container

[Ivan Dimkovic]

Well - theoretically we (Nero) could do CBR, quality (threshold) based VBR, bit rate manageable VBR, ABR with large bit buffer, 2-pass CBR, etc..

I am afraid that we cannot test all that - number of codecs would be too big, I am for using one codec-one mode approach here, otherwise we might be lost in tons of codecs and settings.

[dimzon]

2-pass

WOW!!!!!!!!
It means BEST bitrate distribution @ suggested bitrate!
I really like it!

[guruboolez]

If someone can stream 48 kbps (i.e. if he doesn't have a dial-up), then he should be able to handle VBR without problem. No?

Streaming 48kbps on dial-up IS possible.

Did you try?

[guruboolez]

I dont mind about VBR. But it less predictable for final size. In consequence less fair. Maybe ABR will be good.

Do you mean that forcing CBR good VBR implementations is really something fair? If VBR perform better than CBR, it should be tested. BTW, VBR should be used in the second test (the multiformat one): Vorbis...
My question is: why discarding VBR (VBR has always be considered as better than CBR/ABR on this board)? Predictible size? Bullshit: VBR has always be priviledged in listening tests. Streaming? Nonsense, because VBR could be stream at ~48 kbps with every kind of internet connection excepted dial-up.

[Shade[ST]]

,Dec 14 2005, 05:41 PM]
Streaming 48kbps on dial-up IS possible.

Did you try?

I did. And it worked. It wasn't HE-AAC, but standard aac. "dans un coin perdu du québec, en plus"

[Atlantis]

If someone can stream 48 kbps (i.e. if he doesn't have a dial-up), then he should be able to handle VBR without problem. No?

Streaming 48kbps on dial-up IS possible.

Not here.

[Ivan Dimkovic]

WOW!!!!!!!!
It means BEST bitrate distribution @ suggested bitrate!
I really like it!

Problem with 2-pass is that it is not available in the software being shipped, only in the experimental debug encoder - and making it in would take considerable amount of time and modification to make it there, without internal justification and proof that it is actually better (especially compared to ABR which does not require multipass) - so I wouldn't use it for now.

guruboolez
Do you mean that forcing CBR good VBR implementations is really something fair? If VBR perform better than CBR, it should be tested. BTW, VBR should be used in the second test (the multiformat one): Vorbis...
My question is: why discarding VBR (VBR has always be considered as better than CBR/ABR on this board)? Predictible size? Bullshit: VBR has always be priviledged in listening tests. Streaming? Nonsense, because VBR could be stream at ~48 kbps with every kind of internet connection excepted dial-up.

Ok, we will use something that is average 48 kbps and possible to stream without large buffers - as well as highest quality.

This post has been edited by Ivan Dimkovic: Dec 14 2005, 18:13

[IgorC]

I dont mind about VBR. But it less predictable for final size. In consequence less fair. Maybe ABR will be good.

Do you mean that forcing CBR good VBR implementations is really something fair? If VBR perform better than CBR, it should be tested. BTW, VBR should be used in the second test (the multiformat one): Vorbis...
My question is: why discarding VBR (VBR has always be considered as better than CBR/ABR on this board)? Predictible size? Bullshit: VBR has always be priviledged in listening tests. Streaming? Nonsense, because VBR could be stream at ~48 kbps with every kind of internet connection excepted dial-up.

It´s not b***it. Yes. Predictible size. The idea of HE-AAC2 is save some bits (from 128 kbps to 48 kbps). And If intead of 128 there will be 130-133 kbps then I would say it´s b***it.

[dimzon]

It´s not b***it.  Yes. Predictible  size.  The idea  of HE-AAC2 is save some bits (from 128 kbps to 48 kbps).  And If intead of 128 there will be 130-133 kbps then I would say it´s b***it.

Don't make a drama. VBR is enought predictable - You will get approx +/- 8 kbps final bitrate deviation...

[IgorC]

It´s not b***it.  Yes. Predictible  size.  The idea  of HE-AAC2 is save some bits (from 128 kbps to 48 kbps).  And If intead of 128 there will be 130-133 kbps then I would say it´s b***it.

Don't make a drama. VBR is enought predictable - You will get approx +/- 8 kbps final bitrate deviation...

+/- 8 kbps? Are you serious? No. I want to see 128 kbit/s mp3 and 48 kbps/s HE-aac2. I cant give more bitrate. Not even +/- 2 kbit/s.

VBR is better than ABR. Why is better? VBR has bigger size. Thats all.
ABR two pass should be on par with VBR (or even better). And the size isn´t issue for 135-180kbps. but it´s issue for 48 bkit/s comparing to 128 kbit/s.
But the purpose of this test at low bitrate is to safe some bits.

Guru is pruposing here to use VBR as for 135-180 tests when +/- 100/200 kbyte isn´t issue. But not here.

This post has been edited by IgorC: Dec 14 2005, 18:24

[dimzon]

+/- 8 kbps? Are you serious?  No. I want  to see 128 kbit/s mp3 and 48 kbps/s HE-aac2. I cant give more bitrate.  Not even  +/- 2 kbit/s.

Not for me - I can sacrify bitrate a little to have const quality... I'm calculating target video bitrate after audio encoding 8kbps is nothing for video!

[Gabriel]

VBR/CBR issue:
As you know, modern codecs are using a bit reservoir. It can be directly handled in frames (like mp3), or handled by a regulation part (like some mpeg4 modes).
If your encoder respects the normative constraints regarding CBR, then it is cbr, altough its instantaneous bitrate can vary.

CBR is a way to be sure that you can transmit the stream using a given bandwidth, provided that the decoder has a specific buffer size.

The mp3 cbr is very restricted, as the bit reservoir is only 4088 bits. The AAC reservoir is way higher than that, allowing more large instantaneous fluctuations while still beeing cbr.
If you are using VBR but are enforcing a given average bitrate over a given sliding time slice, then the same bit allocation could be achieved in cbr with a bit reservoir (or whatever its name) that would be the size of your given time slice.

IE: if allowed instantaneous variation is big enough, VBR does not provide any advantage while trying to keep a resonable decoding buffer and a given average bitrate.

question: what is the typical aac buffer size for cbr @48kbps?

edit: bytes -> bits

This post has been edited by Gabriel: Dec 14 2005, 23:43

[guruboolez]

CBR is a way to be sure that you can transmit the stream using a given bandwidth, provided that the decoder has a specific buffer size.

This is true. The question is: do we need to ensure streaming conditions for 48 kbps encodings? If not, I don't see any reason to arbitrary discard VBR. Or is there something special with 48 kbps compared to 128 or 32 kbps?

[guruboolez]

The idea  of HE-AAC2 is save some bits (from 128 kbps to 48 kbps).

Saving bits is the idea of lossy encoding in general (from PCM to encoded file). And VBR is a tool to gain additional space (by maintaining quality at lower bitrate or increasing quality at the same bitrate than CBR).
Consequently, if you're interesting by efficiency (and you are apparently) you should be interested by VBR.

[Ivan Dimkovic]

question: what is the typical aac buffer size for cbr @48kbps?

ISO AAC specifies CBR bit buffer constrains as:

(MAXIMUM_FRAME_SIZE * number_of_channels) - average_frame_length;

Maximum frame size in AAC is 6144 bits

So,

For 48 kHz, Stereo - and 128 kbps AAC bit rate maximum bit reservoir size is 10240 bits

For 22.05 kHz, Stereo (HE-AAC, AAC operates at fs/2) and 48 kbps it should be 7830 bits.

Note, basically you could speficy much bigger bit reservoirs - but then it would take much longer for the decoders to pre-buffer.

This post has been edited by Ivan Dimkovic: Dec 14 2005, 19:10

[dimzon]

The idea  of HE-AAC2 is save some bits (from 128 kbps to 48 kbps).

Saving bits is the idea of lossy encoding in general (from PCM to encoded file). And VBR is a tool to gain additional space (by maintaining quality at lower bitrate or increasing quality at the same bitrate than CBR).
Consequently, if you're interesting by efficiency (and you are apparently) you should be interested by VBR.

100% agreed

[guruboolez]

Something is worrying me.
The purpose of this test is to select the best AAC implementation/profile at 48 kbps, in order to get the best contender for the upcoming multiformat listening test at the same bitrate, right?

Shouldn't be fair to do the same for other competitors? I especially have Vorbis in mind. CVS or Aoyumi? resampled -q-1 or orginal one? Several people have reported here than resampling help a lot Vorbis. I didn't really test it myself, but the few encodings I've done confirmed it (resampling -> less distortions).
In other words, there are different settings for Vorbis. Shouldn't we also perform a pre-listening test to get the best vorbis competitor? Could we consider as fair a dedicated pool for AAC but not for others? Personnaly, I wouldn't. As long as different encoders/settings could pretend to be the best, pools (preliminary listening tests) are needed.
Such pool is necessary for AAC, but I'd say that there elements enough to legitimate such pool for Vorbis (CVS-aoTuV / resampling or not / which sampling rate / ?VBR-ABR?).

This post has been edited by guruboolez: Dec 14 2005, 19:15

[Shade[ST]]

I don't mind preparing a Vorbis + MP3 test at this same bitrate; Testing FHG, aTouV, LAME and regular vorbis at different settings (default, and resampled, I think, should be enough..)

[[JAZ]]

48kbps Streaming IS reasonable :

http://www.polskastacja.pl/

[Sebastian Mares]

Are really 48 kbps encoding useful for streaming?
56K can't stream such encodings, CBR or not. Theoretically, it should be possible, but in fact, it doesn't work.

I can confirm that it works (at least here in Germany, but don't ask me what provider since it was on a mate's PC).

For people having a better download bandwith (the next step is 128 kbps if I'm not wrong), I'm not sure that 48 kbps really makes sense: 64, 80 or even 96 kbps are probably more interesting.

I think single channel ISDN has 64.

[Serge Smirnoff]

Are really 48 kbps encoding useful for streaming?
56K can't stream such encodings, CBR or not. Theoretically, it should be possible, but in fact, it doesn't work.

I can confirm that it works (at least here in Germany, but don't ask me what provider since it was on a mate's PC).

http://www.tuner2.com/ has a lot of 48 kbps streams.