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Encoding with True VBR
paperskyline
post Oct 16 2013, 13:42
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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
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2Bdecided
post Oct 16 2013, 14:23
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QUOTE (paperskyline @ Oct 16 2013, 13:42) *
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?
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paperskyline
post Oct 16 2013, 15:15
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QUOTE (2Bdecided @ Oct 16 2013, 18:53) *
QUOTE (paperskyline @ Oct 16 2013, 13:42) *
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
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paperskyline
post Oct 16 2013, 15:19
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this topic shows what i mean

http://www.hydrogenaudio.org/forums/index....howtopic=102589
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marc2003
post Oct 16 2013, 15:50
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QUOTE (paperskyline @ Oct 16 2013, 13:42) *
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.
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eahm
post Oct 16 2013, 15:51
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QUOTE (paperskyline @ Oct 16 2013, 07:15) *
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.

This post has been edited by eahm: Oct 16 2013, 15:51


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paperskyline
post Oct 16 2013, 17:26
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what exactly is the difference in these settins? and which is better

-V 118 -q1
-V 118 -q2

-q1 or -q2?
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paperskyline
post Oct 16 2013, 17:31
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https://dl.dropboxusercontent.com/u/2280132...tember/qaac.png

this image clearly shows that the file was encoded using CVBR 256kbps
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eahm
post Oct 16 2013, 17:31
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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.


This post has been edited by eahm: Oct 16 2013, 17:32


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LifeWOutMilk
post Oct 16 2013, 17:46
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QUOTE (paperskyline @ Oct 16 2013, 09:26) *
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.
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paperskyline
post Oct 16 2013, 18:04
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http://www.hydrogenaudio.org/forums/index....mp;#entry844379


if that says the itunes settings are " -v256 -q2 "

then how can it be this
https://dl.dropboxusercontent.com/u/2280132...tember/qaac.png

This post has been edited by paperskyline: Oct 16 2013, 18:04
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marc2003
post Oct 16 2013, 18:38
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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.



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paperskyline
post Oct 16 2013, 18:45
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QUOTE (marc2003 @ Oct 16 2013, 23:08) *
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?

This post has been edited by paperskyline: Oct 16 2013, 18:47
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testyou
post Oct 16 2013, 19:08
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You could have read what you quoted.

QUOTE (marc2003 @ Oct 16 2013, 10:38) *
the reason it says 256kbps is because that is the target bitrate.

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marc2003
post Oct 16 2013, 19:22
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^nope, it's a different question. that quote was about QAAC and what it displays in the tool field. this is the question now:

QUOTE (paperskyline @ Oct 16 2013, 18:45) *
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??
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paperskyline
post Oct 16 2013, 19:49
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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
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testyou
post Oct 16 2013, 22:32
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QUOTE (paperskyline @ Oct 16 2013, 11:49) *
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.

This post has been edited by testyou: Oct 16 2013, 22:36
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paperskyline
post Oct 17 2013, 06:06
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QUOTE (testyou @ Oct 17 2013, 03:02) *
QUOTE (paperskyline @ Oct 16 2013, 11:49) *
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
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nu774
post Oct 17 2013, 10:41
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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.
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paperskyline
post Oct 17 2013, 15:02
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QUOTE (nu774 @ Oct 17 2013, 15:11) *
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
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marc2003
post Oct 17 2013, 15:37
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if you want your files to show as 256kbps inside itunes, use itunes to encode them. problem solved. dry.gif
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Nessuno
post Oct 17 2013, 15:46
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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?


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nu774
post Oct 17 2013, 15:50
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QUOTE (paperskyline @ Oct 17 2013, 23:02) *
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
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.
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paperskyline
post Oct 17 2013, 18:01
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QUOTE (nu774 @ Oct 17 2013, 20:20) *
QUOTE (paperskyline @ Oct 17 2013, 23:02) *
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
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
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