exhale - Open Source USAC encoder

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Re: exhale - Open Source USAC encoder

Reply #1125 – 2022-10-29 18:20:13

Not sure if this has been answered / asked before.
I am wondering if Exhale could theoretically be extended to encode AAC-LC files at high bitrate ( 200Kbps )? On the assumption there would be overlap between xhe-AAC and AAC-LC making this easier.

The reason I asked is because we currently lack high quality AAC-LC encoder that is truly open source.

Re: exhale - Open Source USAC encoder

Reply #1126 – 2022-10-29 22:03:05

Even beyond the "theoretically," I'm puzzled: what do you hope that would accomplish?

FDK-AAC is a high quality AAC-LC encoder and is open source.

There are two issues with its license. It contains code that makes use of patented techniques, and it does not come with a grant of any patent licensing. (It explicitly denies granting any such rights, rather than just not including any patent grant as most pre-GPL3 licenses did.)

These make its use in many circumstances legally questionable, and have led some linux distributions etc to call it non-free.

While LC-AAC patents have generally expired, getting a 'patent-free FDK-AAC for LC' may not be as simple as ripping out HE-AAC and HE-AACv2 code. It could take some very careful IP review. Lawyers lawyers lawyers.

Exhale's license has exactly the same problems. xHE-AAC is quite heavily patented. Exhale uses patented techniques and explicitly states that it doesn't/can't give you the right to use those patented techniques.

xHE-AAC is different enough from its predecessors that turning it into an LC encoder, and trying to get rid of patented techniques, would involve radical change. And then you'd still need the lawyers.

(CR Helmrich did have the sense to base his license on a standard license, where AFAIK those responsible for FDK-AAC didn't. But I don't think people object on the basis of any of the rest of FDK-AAC's license text. Yes, it says you can't charge for a copyright license, but that's not actually contravening the Debian Free Software Guidelines or whatever because it doesn't say you can't sell the software, just that you can't charge for a copyright license.)

Re: exhale - Open Source USAC encoder

Reply #1127 – 2022-12-10 10:20:10

So, I tagged the final 1.2.0 release of exhale, see https://gitlab.com/ecodis/exhale/-/releases. If you don't have any issues with exhale 1.1.9, you don't need to re-encode your audio files. This is mainly a bugfix and code stabilization release, with a major version number switch because the API changed a little. The audio quality improvement at ~128 kbps non-SBR and ~96 kbps SBR is very small on average and hardly noticeable.

exhale version 1.2.0 (December 2022)

Changes since version 1.1.9 from December 2021:

C API correction, some code sanitizing (issue #24, merge requests !8–!11, J. Regan)
exhaleLib: code cleanup, very minor quality improvements in CVBR modes f and 5
exhaleLib: 5% speedup of all modes, better target rate matching in CVBR mode g
exhaleLib: work around MinGW compilation hickup (issue #26; thanks, C. Degawa!)

Quote from: iwod on 2022-10-29 18:20:13

Not sure if this has been answered / asked before.
I am wondering if Exhale could theoretically be extended to encode AAC-LC files at high bitrate ( 200Kbps )? On the assumption there would be overlap between xHE-AAC and AAC-LC making this easier.

Theoretically yes, but it's still quite a lot of work, see also post number 9 in this thread. For that reason it's not on my To-Do list.

Happy end-of-year holidays, everyone!

Chris