[opus] Stereo dropping to mono with libopus 1.2 RC

[Matěj Steklík]

Hello, I'm not a programmer or Opus developer but I tried to test the sound 
quality of a music file (Nick Warren - Devil's Elbow, freely available from 
the author's Soundcloud account) encoded with libopus 1.2 RC1. I used 
Windows binaries from free-codecs.com. I noticed that in the case of my 
selected music file (which is generally harsh on lossy codecs as it's 
necessary to use quite a high bitrate to make differences between the 
original and processed file inaudible), there is a long drop of stereo to 
mono (or something which sounds similar) at the beginning of the track and a
few others much shorter during the whole track lenght. The selected bitrate 
is 32 kb/s stereo and everything else on default values. This is not 
happenig with libopus 1.1.x. Also while generally the quality of sound at 32
kb/s is now better with libopus 1.2 than before (except for those stereo to 
mono drops, of course), at 48 kb/s (so probably CELT only) the quality seems
slightly lower than with libopus 1.1.x. The difference is minimal but the 
sound feels a bit more "flat". Stereo to mono drops happens at 48 kb/s as 
well but they're not as noticeable. If you want, I can upload the encoded 
files somewhere so you can check them. I think this should be solved before 
the final 1.2 release as it strongly influence the sound quality of encoded 
files. Thanks for reading.
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