On Fri, Jul 03, 2015 at 12:11:18AM -0300, Claudio Freire wrote: > On Thu, Jul 2, 2015 at 3:13 PM, Rostislav Pehlivanov > <atomnu...@gmail.com> wrote: > > This commit implements intensity stereo coding support to the native aac > > encoder. This is a way to increase the efficiency of the encoder by zeroing > > the right channel's spectral coefficients (in a channel pair) and > > rederiving them in the decoder using information from the scalefactor > > indices of special band types. This commit confomrs to the official ISO > > 13818-7 specifications, although due to their ambiguity certain deviations > > have been taken to ensure maximum sound quality. This commit has been > > extensively tested and has shown to not result in audiable audio artifacts > > unless in extreme cases. This commit also adds an option, aac_is, which has > > the value of 0 by default. Intensity Stereo is part of the scalable aac > > profile and is thus non-default. > > > > The way IS coding works is that it rederives the right channel's spectral > > coefficients from the left channel via the scalefactor index values left in > > the right channel. Since an entire band's spectral coefficients do not need > > to be coded, the encoder's efficiency jumps up and it unzeroes some high > > frequency values which it previously did not have enough bits to encode. > > That way less information is lost than the information lost by rederiving > > the spectral coefficients with some error. This is why the filesize of > > files encoded with IS do not decrease significantly. Users wishing that IS > > coding should reduce filesize are expected to reduce their encoding > > bitrates appropriately. > > > > This is V2 of the commit. The old version did not mark ms_mask as 0 since > > M/S and IS coding are incompactible, which resulted in distortions with M/S > > coding enabled. This version also improves phase detection by measuring it > > for every spectral coefficient in the band and using a simple majority rule > > to determine whether the coefficients are in or out of phase. Also, the > > energy values per spectral coefficient were changed as to reflect the > > official specifications. > >
> This one also looks identical to a WIP I thoroughly tested, so I > believe this means the whole set is good to be pushed, > if a committer > agrees. its really your decission not the commiters you are basically the maintainer/expert about this code applied thanks [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Freedom in capitalist society always remains about the same as it was in ancient Greek republics: Freedom for slave owners. -- Vladimir Lenin
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