Please try to be as much precise as possible and do not digress from the topic
Quote from: paperskyline on 16 October, 2013, 08:42:46 AMPlease try to be as much precise as possible and do not digress from the topicYes SIR!http://wiki.hydrogenaudio.org/index.php?ti...ariable_Bitratehttp://wiki.hydrogenaudio.org/index.php?ti...onstant_BitrateWhy do you believe iTunes uses VBR when it reports CBR?Why would you expect VBR to deliver a constant bitrate?
but appears as "256kbps" when displayed in iTunes?
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
Like paperskyline quoted
--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.
what exactly is the difference in these settins? and which is better-V 118 -q1-V 118 -q2-q1 or -q2?
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.
the reason it says 256kbps is because that is the target bitrate.
What is done here to make those VBR purchased files show as 256kbps in iTunes? now does everyone get the question?
the little help so far was appreciated
Quote from: paperskyline on 16 October, 2013, 02:49:33 PMthe little help so far was appreciatedNo 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.
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
mp4box -std -diso foo.m4a | findstr DecoderConfigDescriptor
so why dosent it show as 256kbps when i encode a track?
Quote from: paperskyline on 17 October, 2013, 10:02:55 AMi 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 itunesAFAIK 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 DecoderConfigDescriptorIn case of Unix like OS, use grep instead of findstr.Quoteso 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.
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 - %dI even tried using "110, 113, 115"Please try to be as much precise as possible and do not digress from the topic