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Topic: QAAC: discussion, questions, feature requests, etc. (Read 687685 times) previous topic - next topic
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QAAC: discussion, questions, feature requests, etc.

Reply #875 –
CVBR is just a slightly improved ABR (allowing more bitrate fluctuations than ABR, but fewer fluctuations than VBR). The bitrate of your files will still vary, but they'll always come out at approximately the bitrate you specify. From moment to moment, the bitrate can go above or below the value you set.

QAAC: discussion, questions, feature requests, etc.

Reply #876 –
Difference between CVBR and ABR in AAC

If you for example encode a song like Lalena from Donovan where there is not much bitrate needed.
I used qaac and used ~256 Kbps for every mode.

Results:
ABR: 5 301 KB (240 Kbps)
CVBR: 5 628 KB (255 Kbps)
VBR: 2 729 KB (123 Kbps)

You see that encoder in VBR mode realizes that it doesn't need very much bitrate for the song and has the lowest size.
Where ABR and CVBR try to stay close to my requested bitrate of ~256 Kbps. So no the bitrate you give to CVBR is not the mininum or maximum bitrate.
From the perpective of quality VBR > CVBR > ABR is better. So if you don't trust VBR or want your files have the same bitrate go for CVBR.
In the lower bitrates VBR should beat CVBR or ABR, but in the higher like 256 Kbps i don't think there would be that much difference to CVBR. (VBR has a bigger bit-reservoir for problematic places in songs.)

And of course you can set a managed bitrate and use minimum and maximum settings if you really need to. Atleast this works in LAME and Vorbis.
Just my experience. Hope didn't get too much wrong. 

QAAC: discussion, questions, feature requests, etc.

Reply #877 –
I was going for tVBR, but as I'm ripping audiobooks and tVBR does not support HE it's a no-go. So I've been using cVBR 80 kbps thus far and it seems to do fine.

QAAC: discussion, questions, feature requests, etc.

Reply #879 –
And recently there was a thread here giving pre-echo samples where borh CVBR and ABR provided the better quality than TVBR did.
I think there is a bias here on HA towards TVBR which is not based on listening tests.
lame3995o -Q1.7 --lowpass 17

QAAC: discussion, questions, feature requests, etc.

Reply #880 –
ABR was better too? I remember some problem samples were CVBR was better, but thougt it was not relevant.
I thought VBR should be better theoretically, but yeah i guess i was wrong. I even remember that listening test now. 

Would be interesting too know if this is the same for Opus.

QAAC: discussion, questions, feature requests, etc.

Reply #881 –
Quote from: decollated on
There was a listening test that ranked CVBR slightly higher than TVBR at ~96kbps:

http://wiki.hydrogenaud.io/index.php?title...Tests#AAC_Tests


Simple reason. TVBR has the lowest bitrate of all tested codecs there. In one sample it uses almost 30% lower bitrate than CVBR. When you use TVBR with settings that don't result in such low bitrate it won't dip behind anything and can use extra bits for difficult parts.

QAAC: discussion, questions, feature requests, etc.

Reply #882 –
How about Apple's "optimise for voice" / "voice filtering" option within iTunes? Is there some way to push this using QAAC?

QAAC: discussion, questions, feature requests, etc.

Reply #883 –
I guess it just uses HE-AAC. Just encode one file in iTunes and check it with MediaInfo.

Edit: Tested it myself. It still uses AAC LC but reduces the file to 22.05 KHz and uses a lower bitrate.
So you will need to use a resampler like : qaac ... -r 22050 ...

QAAC: discussion, questions, feature requests, etc.

Reply #884 –
Are you sure? I tried using Qaac64.exe with --cvbr 48 -q2 --he --rate 32000 --native-resampler=bats,127 and compared it to iTunes - AAC Custom - 48 kbps - 32.000 kHz -- Stereo -- VBR -- HE -- Optimise for Voice and they don't seem to be identical?

Another thing I've noticed, when using HE I'm not able to --r 22050, I can't go lower than 32000?

QAAC: discussion, questions, feature requests, etc.

Reply #885 –
iTunes seems to choose the sample rate depending on the bitrate.
With 24 Kbps my test file is resampled to 8000 kHz.
With other bitrates it was 32000 kHz like you said.

So "optimise for voice" is just resampling and HE can be choosen seperatly.

Preferred Sample Rates

I would encode some files with iTunes in your preferred bitrate and look which sample rate iTunes uses.
And then use this sample rate in qaac.

Result:
Code: [Select]
File 1 (using qaac):
Bit rate mode                            : Variable
Bit rate                                 : 32.9 Kbps
Channel(s)                               : 2 channels
Sampling rate                            : 32.0 KHz / 16.0 KHz
Stream size                              : 959 KiB (98%)

File 2 (using iTunes):
Bit rate mode                            : Variable
Bit rate                                 : 32.0 Kbps
Maximum bit rate                         : 42.9 Kbps
Channel(s)                               : 2 channels
Sampling rate                            : 32.0 KHz / 16.0 KHz
Stream size                              : 958 KiB (98%)

It comes close, but still not complettly identical.
And yes, if i choose 8000 kHz and 80 Kbps, qaac will use more kHz automatically, so you would need to choose a lower bitrate for 8000 kHz to work.

PS: Depending on the bitrate, resampling is maybe not really necessary, since HE AAC uses Spectral band replication for higher frequencies.
But i guess the guys from Apple now what they are doing.

QAAC: discussion, questions, feature requests, etc.

Reply #886 –
Your command line looks fine btw.. Strange that it worked for me.
Are your files that much different?

QAAC: discussion, questions, feature requests, etc.

Reply #887 –
Ignore all that... Seems like iTunes reports HEv2 mono as stereo.. Same goes for dBPowerAMP. How do I downmix stereo to mono using QAAC?

QAAC: discussion, questions, feature requests, etc.

Reply #888 –
Nevermind, I figured it out. Now it's time to compare CVBR 24-64kbps HE Stereo to Mono and figure out whatever settings I find the best for my audiobook library.

QAAC: discussion, questions, feature requests, etc.

Reply #889 –
Hello,

I've been using QAAC for quite some time and I am very happy with it, but in the latest version (2.51) something really annoys me.
Files encoded with TVBR q91 all show up as 192 kbps (VBR) in iTunes. Since TVBR has no target bitrate (only a target quality level), the 192 kbps is meaningless and it should show the average bitrate instead (like it used to do).

QAAC: discussion, questions, feature requests, etc.

Reply #890 –
Quote from: Apollo89 on
I've been using QAAC for quite some time and I am very happy with it, but in the latest version (2.51) something really annoys me.
Files encoded with TVBR q91 all show up as 192 kbps (VBR) in iTunes. Since TVBR has no target bitrate (only a target quality level), the 192 kbps is meaningless and it should show the average bitrate instead (like it used to do).

The following option will remove Encoding Params tag, and iTunes will show actual average bitrate:
Code: [Select]
--long-tag="Encoding Params:"
 

QAAC: discussion, questions, feature requests, etc.

Reply #891 –
Quote from: nu774 on
Quote from: Apollo89 on
I've been using QAAC for quite some time and I am very happy with it, but in the latest version (2.51) something really annoys me.
Files encoded with TVBR q91 all show up as 192 kbps (VBR) in iTunes. Since TVBR has no target bitrate (only a target quality level), the 192 kbps is meaningless and it should show the average bitrate instead (like it used to do).

The following option will remove Encoding Params tag, and iTunes will show actual average bitrate:
Code: [Select]
--long-tag="Encoding Params:"


I'm sorry, I must have missed it but what's the advantage of showing the Encoding Params by default? I just deleted the whole tag...

QAAC: discussion, questions, feature requests, etc.

Reply #893 –
Since the tag is a proprietary form of metadata for iTunes, and qaac is for people who want access to Apple's encoder without having to use iTunes, it seems to me that the tag should be disabled by default, so the burden of using an extra switch is on the few people who care what iTunes says about their AAC files.

QAAC: discussion, questions, feature requests, etc.

Reply #894 –
Quote from: Aleron Ives on
and qaac is for people who want access to Apple's encoder without having to use iTunes


that's a very narrow minded view. i despise itunes myself but i'm sure plenty of itunes users use qaac for the many other features it provides like being able to pipe in any input you want, spawning multiple instances with other front ends, usage with bit perfect CD rippers and so on....

QAAC: discussion, questions, feature requests, etc.

Reply #895 –
Quote from: Aleron Ives on
Since the tag is a proprietary form of metadata for iTunes, and qaac is for people who want access to Apple's encoder without having to use iTunes, it seems to me that the tag should be disabled by default, so the burden of using an extra switch is on the few people who care what iTunes says about their AAC files.

Strictly speaking, it's just that we all use proprietary "iTunes Metadata Format" for tagging m4a, but most of us (including developers) don't know / care about "Encoding Params" tag.
For non iTunes users, presence of "Encoding Params" doesn't make any practical difference other than having one obscure 32 bytes binary tag.
It sounds like you're saying that large majority of non iTunes users hate so much having this tag that they must kill this tag using an extra switch, but why?

QAAC: discussion, questions, feature requests, etc.

Reply #896 –
Are you saying that checking tVBR encoded files in iTunes is meaningless? I was testing various bitrates for my audiobooks and was testing out tVBR with various quality levels and always checked the bitrate reported for iTunes and they always seemed to be the same for every single track from a specific audiobook, but when I compared across audiobooks the reported bitrate in iTunes was very different?

I don't have the files at hand right now, but if I remember correctly Harry Potter og De Vises Stein (Harry Potter Book 1 in Norwegian) ended up with a reported bitrate of around 100-120 kbps using --tvbr 127, while on Harry Potter og Fangen fra Azkaban (Harry Potter Book 3 in Norwegian) each track ended up with a reported bitrate of about 190-200 kbps. If iTunes is not reading tVBR bitrates correctly, how come it didn't not reported the same for both audiobooks? Is it because iTunes is reporting the maximum bitrate used while encoding or something instead of the actual average bitrate?



It doesn't really matter too much for me, I've ended up with going for --cVBR 32 -q2 --he --rate 32000 --native-resampler=bats,127 --matrix-preset mono for my audiobooks and I guess tVBR is of no use when going that low on the bitrate as it cannot be used with HE/HEv2 encoding. After comparing the first 15 minutes of Harry Potte og Fangen fra Azkaban (I selected this one, as it was the only ending with the highest reported bitrate from iTunes when using tVBR 127 so I figured it would be the one that seemed to demand the most bandwidth of all the audiobooks) using --cVBR 24, 32, 48, 64 and 80 in both stereo and mono (HEv2 with Parametric Stereo) it was very hard to really tell them apart when I tested on iPhone 6 Plus using Westone 4R IEM's. If I was listening very closely I could notice a few differences but it was very hard. The only expectation was --cVBR 24, it sounded horrible with lots of echo on the voice even with mono and HEv2.

I guess I could save even more space by going from 32,000 kHz down to 22,050 kHz from what I'm reading online. But it doesn't seem like the Apple Encoder and QAAC allows for anything lower than 32,000 kHz when utilising HE/HEv2 for some reason? If I run the same settings without applying --he it allows for downsampling to 22,050 kHZ sampling rate.

QAAC: discussion, questions, feature requests, etc.

Reply #897 –
Quote from: RamGuy on
Are you saying that checking tVBR encoded files in iTunes is meaningless?

If you want to see actual bitrate, then yes.
Bitrate can be easily computed from size and duration of the stream, but iTunes prefers values in metadata which might be wrong.
Quote
It doesn't really matter too much for me, I've ended up with going for --cVBR 32 -q2 --he --rate 32000 --native-resampler=bats,127 --matrix-preset mono

--native-resampler is terribly inefficient compared to default libsoxr with no practical gain.
Also, HE encoder of Apple might not be so great as their LC encoder, and HEv2 is not supported.
Have you compared to FhG, CT(Dolby) or Nero?

Quote
I guess I could save even more space by going from 32,000 kHz down to 22,050 kHz from what I'm reading online. But it doesn't seem like the Apple Encoder and QAAC allows for anything lower than 32,000 kHz when utilising HE/HEv2 for some reason?

qaac --formats will show you all available combinations of profile/samplerate/channels/bitrate.
22050Hz means freq components above 5.5kHz is encoded by SBR, which might be too low for SBR I guess.

QAAC: discussion, questions, feature requests, etc.

Reply #899 –
I'm pretty sure that Apple Encoder / QAAC supports HEv2? As everything I have encoded using below 64kbps @ mono with HE (in both QAAC and with iTunes itself) has been reported as "Profile: High-Efficiency v2" and is still reported as "Stereo" which might be because iTunes still counts Parametric Stereo as Stereo? dBPowerAMP is reporting it as AAC (LC) + SBS + PS.