[opus] Opus 1.4 is out

[Jean-Marc Valin]

Hi everyone,

I'm happy to announce that Opus 1.4 has just been released. It is 
available at:
https://downloads.xiph.org/releases/opus/opus-1.4.tar.gz

This new release brings the following improvements and fixes:
- Improved tuning of the Opus in-band FEC (LBRR). See 
https://gitlab.xiph.org/xiph/opus/-/issues/2360 for details
- Added an OPUS_SET_INBAND_FEC(2) option that turns on FEC, but does not 
force SILK mode (FEC will be disabled in CELT mode)
- Improved tuning and various fixes to DTX
- Added Meson support, improved CMake support
In addition to the improvements above, this release includes many minor 
bug fixes.

Additionally, we have begun experiments on two upcoming major features:
- neural packet loss concealment:
   https://arxiv.org/pdf/2205.05785.pdf
- deep redundancy:
 
https://www.amazon.science/blog/neural-encoding-enables-more-efficient-recovery-of-lost-audio-packets

Although not included in this release, you can see two IETF drafts 
describing the proposed improvements:
- https://datatracker.ietf.org/doc/draft-valin-opus-extension/
- https://datatracker.ietf.org/doc/draft-valin-opus-dred/

The code is also available on this development branch:
https://gitlab.xiph.org/xiph/opus/-/tree/exp_neural_fec3

Please report any problem you encounter.

Cheers,

         Jean-Marc