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Encoding with True VBR
Recently I have been encoding music with True VBR using foobar & dbpoweramp. everything has been fine so bar, but the bitrate in itunes does not appear as "256kbps".
It appears as " 283, 271, 299, 301,,...etc."
So my question is how does the iTunes Store encode their music in True VBR, but appears as "256kbps" when displayed in iTunes?

My Settings:
dbpoweramp: -V 118 -q2 -r keep -n -R -S -o [outfile] -
foobar: --tvbr 118 --highest - %d

I even tried using "110, 113, 115"

Please try to be as much precise as possible and do not digress from the topic

  • 2Bdecided
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Encoding with True VBR
Reply #1
Please try to be as much precise as possible and do not digress from the topic

Yes SIR!

http://wiki.hydrogenaudio.org/index.php?ti...ariable_Bitrate
http://wiki.hydrogenaudio.org/index.php?ti...onstant_Bitrate

Why do you believe iTunes uses VBR when it reports CBR?

Why would you expect VBR to deliver a constant bitrate?

Encoding with True VBR
Reply #2
Please try to be as much precise as possible and do not digress from the topic

Yes SIR!

http://wiki.hydrogenaudio.org/index.php?ti...ariable_Bitrate
http://wiki.hydrogenaudio.org/index.php?ti...onstant_Bitrate

Why do you believe iTunes uses VBR when it reports CBR?

Why would you expect VBR to deliver a constant bitrate?

well as far as i have read in this site, itunes store music is encoded in True VBR and previously it used to be encoded with "-CVBR 256 -q2".
i even tried to get the exact 256kbps bitrate by using "-CVBR 256 -q2" , but no result

Encoding with True VBR
Reply #3

  • marc2003
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Encoding with True VBR
Reply #4
but appears as "256kbps" when displayed in iTunes?


itunes isn't displaying the real bitrate. that screenshot of mine in the other thread is reporting 256kbps but looking at that same file in foobar, it's 260kbps. if i look at all my other itunes store purchases, they vary between 249 and 285kbps.

try looking at your store purchases in foobar.

  • eahm
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Encoding with True VBR
Reply #5
well as far as i have read in this site, itunes store music is encoded in True VBR and previously it used to be encoded with "-CVBR 256 -q2".
i even tried to get the exact 256kbps bitrate by using "-CVBR 256 -q2" , but no result

You just said you read here that iTunes encodes in TVBR then you show a CVBR command, you need to acknowledge there is a difference between the two first.

Like paperskyline quoted from the qaac website, iTunes uses "-v256 -q2" (CVBR not TVBR) for iTunes Plus setting and "-a128 -q1" (ABR) for iTunes High Quality setting.
  • Last Edit: 16 October, 2013, 10:51:56 AM by eahm

Encoding with True VBR
Reply #6
what exactly is the difference in these settins? and which is better

-V 118 -q1
-V 118 -q2

-q1 or -q2?

Encoding with True VBR
Reply #7
https://dl.dropboxusercontent.com/u/2280132...tember/qaac.png

this image clearly shows that the file was encoded using CVBR 256kbps

  • eahm
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Encoding with True VBR
Reply #8
Quote
Like paperskyline quoted

I meant testyou here: http://www.hydrogenaudio.org/forums/index....st&p=844379


From https://github.com/nu774/qaac/wiki/Encoder-configuration:

Quote
--quality is an another option concerning quality, and you might be confused. This is the same with the previous dialog's "Quality". This option controls not file size, but the trade off between encoding speed/quality. Bigger value means higher quality, and slower encoding speed. By default, qaac uses 2 (best quality, slowest speed). Usually, higher -q setting seems to produce smaller file.
  • Last Edit: 16 October, 2013, 12:32:35 PM by eahm

Encoding with True VBR
Reply #9
what exactly is the difference in these settins? and which is better

-V 118 -q1
-V 118 -q2

-q1 or -q2?



From https://github.com/nu774/qaac/wiki/Encoder-configuration
Quote
--quality is an another option concerning quality, and you might be confused. This is the same with the previous dialog's "Quality". This option controls not file size, but the trade off between encoding speed/quality. Bigger value means higher quality, and slower encoding speed. By default, qaac uses 2 (best quality, slowest speed). Usually, higher -q setting seems to produce smaller file.

Encoding with True VBR
Reply #10
  • Last Edit: 16 October, 2013, 01:04:57 PM by paperskyline

  • marc2003
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Encoding with True VBR
Reply #11
you're looking at what QAAC has written to the tool field. the reason it says 256kbps is because that is the target bitrate. look to the left and you'll see the real bitrate for that particular file is 262kbps.

itunes does confuse things further as i already explained above. looking at the "real" bitrate in the "get info" dialog always reports 256kbps for itunes store files even though their bitrates are VBR.

this screenshot shows an EP purchased from the itunes store. note how that itunes is reporting 256kbps for all of them. but when i load the same files in foobar, they are clearly VBR.




Encoding with True VBR
Reply #12
you're looking at what QAAC has written to the tool field. the reason it says 256kbps is because that is the target bitrate. look to the left and you'll see the real bitrate for that particular file is 262kbps.

itunes does confuse things further as i already explained above. looking at the "real" bitrate in the "get info" dialog always reports 256kbps for itunes store files even though their bitrates are VBR.

this screenshot shows an EP purchased from the itunes store. note how that itunes is reporting 256kbps for all of them. but when i load the same files in foobar, they are clearly VBR.


this was a convincing answer, so now the original question is that this picture shows the files are 256kbps when seen in iTunes but why aren't my files showing as 256kbps and instead it shows as "253, 231, 286... etc" in iTunes?
What is done here to make those VBR purchased files show as 256kbps in iTunes? now does everyone get the question?
  • Last Edit: 16 October, 2013, 01:47:07 PM by paperskyline

  • testyou
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Encoding with True VBR
Reply #13
You could have read what you quoted.

the reason it says 256kbps is because that is the target bitrate.


  • marc2003
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Encoding with True VBR
Reply #14
^nope, it's a different question. that quote was about QAAC and what it displays in the tool field. this is the question now:

What is done here to make those VBR purchased files show as 256kbps in iTunes? now does everyone get the question?


obviously there is metadata inside purchased files so itunes knows this and for whatever reason chooses to display 256kbps instead of the actual bitrate. as for why? you'd have to ask apple that. i'm just guessing now but one reason could be to stop people thinking they have low quality files if they have music that isn't complex and have much lower bitrates??

Encoding with True VBR
Reply #15
i know it is a very hard question. as this is a forum for AAC discussions, thought i'd post my queries here.
anyways thanks to those for involving in this topic. the little help so far was appreciated

  • testyou
  • [*][*][*]
Encoding with True VBR
Reply #16
the little help so far was appreciated

No need to get testy.  I found your sentences hard to understand.

I think I see what you mean now.
Well I remember reading on these forums (I have no proof however) that iTunes might include different(?) codec information than what some other tools do.
If so, then when iTunes encodes a file in CVBR mode with target bitrate of 256kbps, that file is subsequently shown in iTunes as 256kbps like you see above.
And when an alternative tool is accessing the same files to encode like with qaac, it does not include that same information in the header.
  • Last Edit: 16 October, 2013, 05:36:56 PM by testyou

Encoding with True VBR
Reply #17
the little help so far was appreciated

No need to get testy.  I found your sentences hard to understand.

I think I see what you mean now.
Well I remember reading on these forums (I have no proof however) that iTunes might include different(?) codec information than what some other tools do.
If so, then when iTunes encodes a file in CVBR mode with target bitrate of 256kbps, that file is subsequently shown in iTunes as 256kbps like you see above.
And when an alternative tool is accessing the same files to encode like with qaac, it does not include that same information in the header.


i guess that is the only thinkable answer at the moment

  • nu774
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Encoding with True VBR
Reply #18
It's not written as a tag field. Unlike tag, this is pretty much standard of ISO MPEG4 and is written in DecoderConfigDescriptor, avgBitrate field in moov.trak.mdia.minf.stbl.stsd.mp4a.esds box.
It's just that iTunes (for some reason) writes constant value even when it's encoding with VBR mode.
In case of qaac, actual bitrate is written.

Encoding with True VBR
Reply #19
It's not written as a tag field. Unlike tag, this is pretty much standard of ISO MPEG4 and is written in DecoderConfigDescriptor, avgBitrate field in moov.trak.mdia.minf.stbl.stsd.mp4a.esds box.
It's just that iTunes (for some reason) writes constant value even when it's encoding with VBR mode.
In case of qaac, actual bitrate is written.


i get that. but itunes store doesn't encode their music using itunes, they use an external encoder. itunes encodes all the files in vbr too, but it appears as 256kbps in itunes, so why dosent it show as 256kbps when i encode a track?
what is the different procedure used to make it look as 256kbps?
*Note*: https://dl.dropboxusercontent.com/u/2280132...tember/qaac.png

  • marc2003
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Encoding with True VBR
Reply #20
if you want your files to show as 256kbps inside itunes, use itunes to encode them. problem solved. 

  • Nessuno
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Encoding with True VBR
Reply #21
And, in the first place, what's the point in looking for a particular bitrate when using VBR and the QT encoder itself in this case asks for a quality parameter, not a target bitrate?
... I live by long distance.

  • nu774
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Encoding with True VBR
Reply #22
i get that. but itunes store doesn't encode their music using itunes, they use an external encoder. itunes encodes all the files in vbr too, but it appears as 256kbps in itunes

AFAIK they are using afconvert. If it's shown as 256kbps (like iTunes), then probably it means that afconvert do the same as iTunes, but I cannot say for sure since I have no access to afconvert.
You can see the value by the following command line:
Code: [Select]
mp4box -std -diso foo.m4a | findstr DecoderConfigDescriptor

In case of Unix like OS, use grep instead of findstr.

Quote
so why dosent it show as 256kbps when i encode a track?

Do you mean "encode a track by qaac"?
I already wrote the reason. iTunes (and probably afconvert) writes target bitrate into avgBitrate field, and qaac writes actual average bitrate. So they look different.
However, strictly speaking both are not spec compliant. That field shall be zero in case of VBR, acording to ISO 14496-1.

Encoding with True VBR
Reply #23
i get that. but itunes store doesn't encode their music using itunes, they use an external encoder. itunes encodes all the files in vbr too, but it appears as 256kbps in itunes

AFAIK they are using afconvert. If it's shown as 256kbps (like iTunes), then probably it means that afconvert do the same as iTunes, but I cannot say for sure since I have no access to afconvert.
You can see the value by the following command line:
Code: [Select]
mp4box -std -diso foo.m4a | findstr DecoderConfigDescriptor

In case of Unix like OS, use grep instead of findstr.

Quote
so why dosent it show as 256kbps when i encode a track?

Do you mean "encode a track by qaac"?
I already wrote the reason. iTunes (and probably afconvert) writes target bitrate into avgBitrate field, and qaac writes actual average bitrate. So they look different.
However, strictly speaking both are not spec compliant. That field shall be zero in case of VBR, acording to ISO 14496-1.

this was enlightening. this is the info that i exactly wanted. thanks

Encoding with True VBR
Reply #24
Recently I have been encoding music with True VBR using foobar & dbpoweramp. everything has been fine so bar, but the bitrate in itunes does not appear as "256kbps".
It appears as " 283, 271, 299, 301,,...etc."
So my question is how does the iTunes Store encode their music in True VBR, but appears as "256kbps" when displayed in iTunes?

My Settings:
dbpoweramp: -V 118 -q2 -r keep -n -R -S -o [outfile] -
foobar: --tvbr 118 --highest - %d

I even tried using "110, 113, 115"

Please try to be as much precise as possible and do not digress from the topic

I have the same problem. The correct settings for the iTunes Plus preset are "-v 256 -q 2 --no-smart-padding" (CVBR 256 kbps High Quality). The file size is very close to iTunes encoded files, but only the iTunes encoded files show "256 kbps (VBR)". My files just show "268 kbps" etc.