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Re: Opus 1.2 alpha

Reply #50
I wonder which codec is being used with --bitrate 32 --framesize 60 --cvbr --downmix-mono setting right now in 1.2-alpha. Seems like a nice spot for very low bitrate generic music. It's still noticable not transparent, but artifacts are not utterly annoying (at least compared to HE-AACv1 mono at this bitrate). For me it's even listenable with headphones on. But it sounds a bit different, like it was using SILK instead of CELT. 
I could be using either SILK or CELT, depending on whether it thinks it's speech or music. Also, don't use --framesize 60 and --cvbr. They make things worse.

Re: Opus 1.2 alpha

Reply #51
Oh, it's interesting you say those. I thought framesize 60 improves compression a bit (while reducing transient representation as a tradeoff). Other codecs like HE-AAC and USAC seems to make a benefit from 100ms+ delay in those extreme low bitrates. I'm surprised it's not the case with Opus.

CVBR was used because I'm testing for mobile broadcasting so bitrates shouldn't fluctuate too much. But hard-cbr seemed too aggressive.
WavPack -b4x4hc
Opus --cvbr --bitrate 256 --framesize 5

Re: Opus 1.2 alpha

Reply #52
Oh, it's interesting you say those. I thought framesize 60 improves compression a bit (while reducing transient representation as a tradeoff). Other codecs like HE-AAC and USAC seems to make a benefit from 100ms+ delay in those extreme low bitrates. I'm surprised it's not the case with Opus.
In Opus, frames of 60 ms are just a concatenation of 3 20-ms frames, except that the encoder's decisions are slightly worse (not a big deal, but it's definitely not an improvement).

CVBR was used because I'm testing for mobile broadcasting so bitrates shouldn't fluctuate too much. But hard-cbr seemed too aggressive.
FYI, Opus CVBR is the same as what other codecs call CBR. That's because what codecs like MP3 and AAC call "CBR" in in fact constrained VBR hidden behind a bit reservoir. What Opus calls CBR is hard CBR with no bit reservoir.

Re: Opus 1.2 alpha

Reply #53
Thank you for the explanation! :)
WavPack -b4x4hc
Opus --cvbr --bitrate 256 --framesize 5

Re: Opus 1.2 alpha

Reply #54
Hmm, just tested BuildC from the other listening tests forum thread and wanted to provide some (hopefully useful) input. The guitar sounds at the very beginning of Shiga Lin's song "Once Said" is still causing some big difficulties for the codec. The HE-AAC output from iTunes seems to handle things a bit more gracefully (quite possibly at the loss of transparency, but I don't have the ears for that). Both are at 64 kbps. Other than that, great work on the improvements!

 

 
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