[FFmpeg-trac] #5759(avcodec:new): libopusenc: make surround masking and LFE optimizations default, optional and independent of mapping family

[FFmpeg]

#5759: libopusenc: make surround masking and LFE optimizations default, optional
and independent of mapping family
-------------------------------------+-------------------------------------
             Reporter:  Peter.White  |                     Type:
               Status:  new          |  enhancement
            Component:  avcodec      |                 Priority:  wish
             Keywords:               |                  Version:  git-
  mapping_family                     |  master
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
-------------------------------------+-------------------------------------
 Summary of the bug:

 Currently there is no way, that I know of, to enable surround masking and
 LFE optimizations in the libopus encoder, other than enabling
 -mapping_family 1. These optimizations result in a significantly lower
 bitrate at virtually the same perceptual quality.

 How to reproduce:
 {{{
 % ffmpeg -i surround_input -c:a libopus output
 ffmpeg version N-81293-g81fcd91 Copyright (c) 2000-2016 the FFmpeg
 developers
 }}}

 This by default disables above mentioned optimizations, as stated by the
 docs for the mapping family option. To enable them one needs to set
 mapping family to 1, which does not make much sense for input with less
 than 3 channels.

 The current release of opusenc
 {{{
 opusenc --version
 opusenc opus-tools 0.1.9 (using libopus 1.1.3)
 Copyright (C) 2008-2013 Xiph.Org Foundation
 }}}
 does enable those optimizations by default, easily observable by encoding
 the same input with opusenc:

 {{{
 opusenc surround_input output
 }}}
 I have seen differences in bitrate of up to 20% with this. Plus, I have
 found no way to even disable them with opusenc. So, if the opus developers
 think it safe to enable these settings and not even provide an option to
 disable them, I think it should be just as safe for ffmpeg to enable them
 and provide an option to disable.

 Or, leave the defaults as is and provide an option to enable the
 optimizations separately from mapping family. That way one can still
 leverage the automatic mapping family setting with -mapping_family -1 but
 on top of that enable surround masking and LFE optimizations at will. Of
 course that should be a no-op if the number of channels is less than 3.
 Or, more precisely:
 {{{ffmpeg -i input -lfe_optimizations -surround_masking output.opus}}}
 should enable LFE optimizations only if there actually is an LFE channel
 and likewise for surround masking.

--
Ticket URL: <https://trac.ffmpeg.org/ticket/5759>
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