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Old 7th November 2008, 01:18   #1  |  Link
David1105
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AAC audio and bitrate

Is it possible at all for an AAC audio file to be of Constant Bit Rate (CBR), instead of VBR or ABR? Reading info from various sources inidcates different things to me so far...

Why MediaInfo always displays output AAC audio file as VBR if using FFMPEG with libfaac codec?

If possible at all for to config libfaac to output CBR? Or does anyone have a build of libfaac codec which support CBR?

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Old 7th November 2008, 01:31   #2  |  Link
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Quote:
Originally Posted by David1105 View Post
Is it possible at all for an AAC audio file to be of Constant Bit Rate (CBR), instead of VBR or ABR? Reading info from various sources inidcates different things to me so far...

Why MediaInfo always displays output AAC audio file as VBR if using FFMPEG with libfaac codec?

If possible at all for to config libfaac to output CBR? Or does anyone have a build of libfaac codec which support CBR?
Yes, it is possible for AAC to use CBR mode. Not all encoders support CBR mode though. One of which supports it is neroAacEnc through the -cbr option

MediaInfo displays VBR because FAAC only encodes in VBR. It does not support CBR encodings
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Old 7th November 2008, 01:51   #3  |  Link
David1105
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Originally Posted by froggy1 View Post
Yes, it is possible for AAC to use CBR mode. Not all encoders support CBR mode though. One of which supports it is neroAacEnc through the -cbr option
I tried also with neroAacEnc with the following

neroaacenc -br 1 -cbr 128000 -if input.wav -of output.m4a

But MediaInfo still says:

Bit rate mode : Variable
Bit rate : 128 Kbps
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Old 7th November 2008, 01:56   #4  |  Link
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Originally Posted by David1105 View Post
I tried also with neroAacEnc with the following

neroaacenc -br 1 -cbr 128000 -if input.wav -of output.m4a

But MediaInfo still says:

Bit rate mode : Variable
Bit rate : 128 Kbps
it should be neroAacEnc -cbr 128000 -if input.wav -of output.m4a

you cannot mix both -br and -cbr. You can either use quality-based encoding (-q), ABR-based encoding (-br) or CBR-based encoding (-cbr)

if MediaInfo still shows its VBR, then there's something wrong with it
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Old 7th November 2008, 02:07   #5  |  Link
David1105
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Originally Posted by froggy1 View Post
it should be neroAacEnc -cbr 128000 -if input.wav -of output.m4a

you cannot mix both -br and -cbr. You can either use quality-based encoding (-q), ABR-based encoding (-br) or CBR-based encoding (-cbr)

if MediaInfo still shows its VBR, then there's something wrong with it
I tried without -br again, and MediaInfo displays the same.

Wrong with what? MediaInfo or neroAacEnc?
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Old 7th November 2008, 02:17   #6  |  Link
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Originally Posted by David1105 View Post
I tried without -br again, and MediaInfo displays the same.

Wrong with what? MediaInfo or neroAacEnc?
MediaInfo
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Old 7th November 2008, 02:37   #7  |  Link
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Originally Posted by froggy1 View Post
MediaInfo
I'm glad to hear of that...

By the way, why you are so sure about neroAacEnc?
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Old 7th November 2008, 02:42   #8  |  Link
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Originally Posted by David1105 View Post
I'm glad to hear of that...

By the way, why you are so sure about neroAacEnc?
I never said I was sure about it. if neroAacEnc didn't support CBR-mode encoding, the -cbr option won't be there. -cbr is mostly intended to be used for streaming. I'm not really 100% sure if it's "hard" CBR or if neroAacEnc just limits bitrate bursts during -cbr encoding.
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Old 8th November 2008, 09:35   #9  |  Link
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IIRC cbr in aac is never truly cbr, but vbr with a very small buffer size. The nero guys discussed this on hydrogenaudio.org and if you search there I am sure you can find a good explaination.
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