Nero AAC Quality vs. Bitrate

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Nero AAC Quality vs. Bitrate

2007-06-29 01:12:11

I recently started encoding to AAC with Nero and was a little surprised that there wasnt a target bitrate vbr like in lame. I like the idea of 'quality' that Nero has (however it actually computes this), but since I only use lossy files for portable use I also appreciate the file size predicatability of a target bitrate. Most of my music tends to be 'rock-ish' and therefore more compressed resulting in bitrates in the 170-210kbps range with a quality setting of 0.45. Ive tested lower quality settings with 0.35 settling around 118-130kbps, with fairly transparent output (I have not ABX'd).

I assume on different music the quality would be too low and result in low bitrate (q 0.35 = 99kbps in the stickied guide). So, should I use ABR? That would ensure that my file sizes are predictable. But I would lose some of the benefit of the encoder giving say, 141kbps on a particularily difficult to compress song (I consider a range of 115-150kbps a good range for filesize). I could also convince myself that a lower quality would have fewer noticeable artifacts on a rock song, then a string solo, although I have no samples etc. on which to base this.

So I could write a quick script that would start at 0.40 quality and examine the bitrate after encoding and if the bitrate fell outside my range, it would try again with a lower quality (say 0.38) and visa-versa. Actually I would probably start at 0.35 since this seems to fit my average musical taste. However, would this actually buy me anything over ABR? Other than a warm, snuggly, (placebo) feeling? And of course the obvious question: which setting did I miss that will just do this for me already?

That turned out a bit long...thanks for reading.

Nero AAC Quality vs. Bitrate

Reply #1 – 2007-06-29 04:09:23

Nero does have a target vbr mode (ABR)

Code: [Select]

*************************************************************
*                                                           *
*  Nero Digital Audio Reference MPEG-4 & 3GPP Audio Encoder *
*  Copyright © 2006 Nero AG                               *
*  All Rights Reserved Worldwide                            *
*                                                           *
*  Package build date: Feb 12 2007                          *
*                                                           *
*  See -help for a complete list of available parameters.   *
*                                                           *
*************************************************************

Usage:
neroAacEnc.exe [options] -if <input-file> -of <output-file>
Where:
<input-file>  : Path to source file to encode.
                The file must be in Microsoft WAV format and contain PCM data.
                Specify - to encode from stdin.
                Note that multiple input files can be specified, they will be
                encoded together into a single output file with chapter marks
                indicating source file divisions.
<output-file> : Path to output file to encode to, in MP4 format.

  ==== Available options: ====

Quality/bitrate control:
-q <number>   : Enables "target quality" mode.
                <number> is a floating-point number in 0...1 range.
-br <number>  : Specifies "target bitrate" mode.
                <number> is target bitrate in bits per second.
-cbr <number> : Specifies "target bitrate (streaming)" mode.
                <number> is target bitrate in bits per second.
                When neither of above quality/bitrate options is used,
                the encoder defaults to equivalent of -q 0.5

Multipass encoding:
-2pass        : Enables two-pass encoding mode.
                Note that two-pass more requires a physical file as input,
                rather than stdin.
-2passperiod  : Overrides two-pass encoding bitrate averaging period,
  <number>    : in milliseconds.
              : Specify zero to use least restrictive value possible (default).

Advanced features / troubleshooting:
-lc           : Forces use of LC AAC profile (HE features disabled)
-he           : Forces use of HE AAC profile (HEv2 features disabled)
-hev2         : Forces use of HEv2 AAC profile
                Note that the above switches (-lc, -he, -hev2) should not be
                used; optimal AAC profile is automatically determined from
                quality/bitrate settings when no override is specified.
-hinttrack      Generates an RTP hint track in output MP4 file.
-ignorelength : Ignores length signaled by WAV headers of input file.
                Useful for certain frontends using stdin.

you'll probably want to use -br mode with -2pass to get the bitrate bang on, but it will take longer to encode

EDIT: the -2pass might not be needed, i just tried it out two files, one with -2pass and the other without and the bitrate was identical.

Nero AAC Quality vs. Bitrate

Reply #2 – 2007-06-29 16:44:43

Vicious Duck, I likened the BR setting to ABR (average bit rate). That is probably what I will end up using, but I was curious if there was any percieved benefit to allowing for a larger "range" of bitrates. Hypothetically the Quality setting will identify songs that are harder to encode and give them an extra 20kbps or so. In my tests BR will always land within 2-3kbps. What do you think?

Nero AAC Quality vs. Bitrate

Reply #3 – 2007-06-29 19:46:09

Quote from: trainee on 2007-06-29 16:44:43

Vicious Duck, I likened the BR setting to ABR (average bit rate). That is probably what I will end up using, but I was curious if there was any percieved benefit to allowing for a larger "range" of bitrates. Hypothetically the Quality setting will identify songs that are harder to encode and give them an extra 20kbps or so. In my tests BR will always land within 2-3kbps. What do you think?

Well, theoretically speaking, VBR almost always gives you better results than ABR. Then again, that is just theoretically and not considering killer samples that do better with 300kbps ABR. I would think that it would be safe to use ABR if you are looking for a predictable file size instead of focusing purely on quality.

Nero AAC Quality vs. Bitrate

Reply #4 – 2007-06-30 01:38:05

Quote from: kornchild2002 on 2007-06-29 19:46:09

Well, theoretically speaking, VBR almost always gives you better results than ABR. Then again, that is just theoretically and not considering killer samples that do better with 300kbps ABR. I would think that it would be safe to use ABR if you are looking for a predictable file size instead of focusing purely on quality.

There shouldn't be a need for ABR defense with AAC. VBR is robust enough.

Nero AAC Quality vs. Bitrate

Reply #5 – 2007-06-30 02:09:24

Quote from: shadowking on 2007-06-30 01:38:05

There shouldn't be a need for ABR defense with AAC. VBR is robust enough.

So wait...I should use VBR and tweak the Quality setting to get it to my target bitrate range? I guess thats 2 votes ABR, 1 vote VBR, 1 undecided (me).

Nero AAC Quality vs. Bitrate

Reply #6 – 2007-06-30 02:33:19

Quote from: trainee on 2007-06-30 02:09:24

Quote from: shadowking on 2007-06-30 01:38:05

There shouldn't be a need for ABR defense with AAC. VBR is robust enough.

So wait...I should use VBR and tweak the Quality setting to get it to my target bitrate range? I guess thats 2 votes ABR, 1 vote VBR, 1 undecided (me).

Yes use vbr in aac. In mp3 vbr works of the psymodel which isn't perfect. In a bad scenario the psymodel gives the wrong info to vbr and quality doesn't go up even though you throw more and more bits. I have seen several cases like this in mp3 vbr - high bitrate ABR can give improvements in this case. I have not seen this behaviour in AAC vbr at all. Most extreme cases resolve at 200~250k VBR. Only one I know at >300k and ABR was *worse*.

Nero AAC Quality vs. Bitrate

Reply #7 – 2007-07-02 07:45:05

I had to choose between "-br 90000" or "-q 0.31".

My goal was to get about 50 hrs. onto a 2 GB USB stick. Very different music genres.

What happened with -q 0.31: Some albums were encoded at <70 kbps av., some at more than 110. I'm very sure if you would see such a result, you'd start tuning, e.g. start trying 0.35 for the <70kbps encode... It's a psychological question.

My advice: If bitrate/size is an important part of the mission, don't waste your time, trust in the nero developers and the sufficient flexibility of the abr mode and thus use -br <n>.

Nero AAC Quality vs. Bitrate

Reply #8 – 2007-07-02 13:32:13

Quote from: Squeller on 2007-07-02 07:45:05

I had to choose between "-br 90000" or "-q 0.31".

My goal was to get about 50 hrs. onto a 2 GB USB stick. Very different music genres.

What happened with -q 0.31: Some albums were encoded at <70 kbps av., some at more than 110. I'm very sure if you would see such a result, you'd start tuning, e.g. start trying 0.35 for the <70kbps encode... It's a psychological question.

My advice: If bitrate/size is an important part of the mission, don't waste your time, trust in the nero developers and the sufficient flexibility of the abr mode and thus use -br <n>.

Am I understanding this correctly??? You say "don't trust developers on his implementation of the -q setting (VBR)", and at the same time " trust the developers on the abr mode" . All, because VBR is *doing* what it is supposed to do, but you ignore?

Yea... good advice..

Nero AAC Quality vs. Bitrate

Reply #9 – 2007-07-02 14:08:53

I've done very little encoding below a target bitrate of 125, but my personal experience has shown that Nero's bitrate range @ -q .4 was much tighter than LAME or Vorbis at V5 or q4 respectively. I can't remember a single track above 140 in Nero AAC, and that was testing with a lot of punk rock stuff.

For me, the ABR/VBR dilemma has always come down to whether filesize or quality is higher priority.

Nero AAC Quality vs. Bitrate

Reply #10 – 2007-07-02 18:02:33

I'm more of a Mac user, so tend to encode with the Core Audio/iTunes encoder. However, I have got a Windows machine and did put Nero on that.

Here's an interesting case: I tried encoding Sting's "Songs from the Labyrinth". On that album, Sting intersperses the songs with spoken word. With the Core Audio encoder set to 160 kbps VBR everything is encoded at around 160 kbps, but Nero (in most cases; sometimes there are background noises, which probably affect things) drops the bitrate down when dealing with speech. The Core Audio encoder is very good, but I thought that was an interesting demonstration of the superior flexibility of Nero's encoder. It matters, if space if limited.

Nero AAC Quality vs. Bitrate

Reply #11 – 2007-07-02 18:40:13

Quote from: link=msg=502114 date=0

Am I understanding this correctly??? You say "don't trust developers on his implementation of the -q setting (VBR)"

No. I'm saying if size is a goal (e.g. my plan was 25 hrs/GB) and vbr clocks in far lower than the average "planned" bitrate in certain albums, then I prefer to force an average bitrate with abr. In high bitrate encodings I have no problem to let vbr do it's job, bit in lower areas I feel uncomfortable seeing vbr acting close to a bleeding edge. E.g. I currently do encodings for my car stereo and vbr encodings vary from 70 to 110 kbps. Yes, and I feel a bit more comfortable when using -br 90000, because I have some trust in the abr algorithms as well as the aac format (compared with mp3). Not a problem if this is kind of vbr blasphemy for you.

OK, vice versa now: Am I understanding this correctly??? You say "don't trust developers on his implementation of the -br setting (ABR)?

Nero AAC Quality vs. Bitrate

Reply #12 – 2007-07-02 19:52:14

Can't do much about psychological effects, or at least i don't plan to.
I just wanted to point out that bitrate is not equal to quality, and i was contrary to the bit where you suggested to use a higher -q setting if getting lower than expected bitrate.

I simply would be happy fitting one or two more songs, supposedly retaining still the wanted quality.

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