[FFmpeg-devel] [PATCH] libopus: support disabling phase inversion.

[Derek Buitenhuis]

On 1/22/2018 3:16 PM, mrdegier at gmail.com wrote:
> From: Menno <mrdegier at gmail.com>
> 
> Signed-off-by: Menno <mrdegier at gmail.com>
> ---
>  doc/encoders.texi       |  5 +++++
>  libavcodec/libopusenc.c | 14 ++++++++++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/doc/encoders.texi b/doc/encoders.texi
> index 6a410a8cb6..5cd8b1a064 100644
> --- a/doc/encoders.texi
> +++ b/doc/encoders.texi
> @@ -981,6 +981,11 @@ Other values include 0 for mono and stereo, 1 for surround sound with masking
>  and LFE bandwidth optimizations, and 255 for independent streams with an
>  unspecified channel layout.
>  
> + at item disable_phase_inversion (N.A.) (requires libopus >= 1.2)
> +If set to 1, disables the use of phase inversion for intensity stereo,
> +improving the quality of mono downmixes, but slightly reducing normal stereo
> +quality. The default is 0 (phase inversion enabled).

Maybe be a bit more drastic. IMO it more than "improves the quality" of
mono, but brings it from completely unlistenable to listenable. 

- Derek

> +
>  @end table
>  
>  @anchor{libshine}
> diff --git a/libavcodec/libopusenc.c b/libavcodec/libopusenc.c
> index b449497d15..3ad10502fc 100644
> --- a/libavcodec/libopusenc.c
> +++ b/libavcodec/libopusenc.c
> @@ -39,6 +39,9 @@ typedef struct LibopusEncOpts {
>      int packet_size;
>      int max_bandwidth;
>      int mapping_family;
> +#ifdef OPUS_SET_PHASE_INVERSION_DISABLED_REQUEST
> +    int disable_phase_inversion;
> +#endif
>  } LibopusEncOpts;
>  
>  typedef struct LibopusEncContext {
> @@ -154,6 +157,14 @@ static int libopus_configure_encoder(AVCodecContext *avctx, OpusMSEncoder *enc,
>                     "Unable to set maximum bandwidth: %s\n", opus_strerror(ret));
>      }
>  
> +#ifdef OPUS_SET_PHASE_INVERSION_DISABLED_REQUEST
> +    ret = opus_multistream_encoder_ctl(enc,
> +                                       OPUS_SET_PHASE_INVERSION_DISABLED(opts->disable_phase_inversion));
> +    if (ret != OPUS_OK)
> +        av_log(avctx, AV_LOG_WARNING,
> +               "Unable to disable phase inversion: %s\n",
> +               opus_strerror(ret));
> +#endif
>      return OPUS_OK;
>  }
>  
> @@ -530,6 +541,9 @@ static const AVOption libopus_options[] = {
>          { "on",             "Use variable bit rate", 0, AV_OPT_TYPE_CONST, { .i64 = 1 }, 0, 0, FLAGS, "vbr" },
>          { "constrained",    "Use constrained VBR",   0, AV_OPT_TYPE_CONST, { .i64 = 2 }, 0, 0, FLAGS, "vbr" },
>      { "mapping_family", "Channel Mapping Family",              OFFSET(mapping_family), AV_OPT_TYPE_INT,   { .i64 = -1 },   -1,  255,  FLAGS, "mapping_family" },
> +#ifdef OPUS_SET_PHASE_INVERSION_DISABLED_REQUEST
> +    { "disable_phase_inversion", "Disable phase inversion",              OFFSET(disable_phase_inversion), AV_OPT_TYPE_INT,   { .i64 = 0 },   0,  1,  FLAGS  },
> +#endif
>      { NULL },
>  };
>  
>