[opus] API for checking whether the encoder is in DTX (PR #107)

[Gustaf Ullberg]

Thank you Mark.

I agree and have now updated the pull request with a new commit, addressing
your comments.
Please take a look.

/Gustaf

On Fri, 5 Apr 2019 at 11:41, Mark Harris <mark.hsj at gmail.com> wrote:

> On 2019-04-01 3:37, Gustaf Ullberg wrote:
> > Hi everyone,
> >
> > Some time ago, I sent a pull request
> > <https://github.com/xiph/opus/pull/107> to the Opus github page.
> > Jean-Marc asked me to post it to the mailing list so everyone can have a
> > look at it.
> >
> > You can find the description and code changes below. Please let me know
> > if you have any questions or concerns.
> >
> > Best regards
> > Gustaf Ullberg
> >
> > In WebRTC, we would like to be able to differentiate between "normal"
> > frames and the comfort noise update frames that are encoded before and
> > in-between DTX frames. These CNG update frames could then be flagged for
> > routing or statistics reasons. Such flagging could also make it easier
> > for a jitterbuffer to differ DTX from packet loss.
> >
> > This PR implements an encoder CTL named OPUS_GET_IN_DTX. OPUS_GET_IN_DTX
> > returns 1 if the last encoded frame was either a DTX frame, or a CNG
> > update frame that is sent every 420 ms between the DTX frames.
> >
> > This is achieved by checking if the number of consecutive inactive
> > frames (nb_no_activity_frames) is greater or equal to
> > NB_SPEECH_FRAMES_BEFORE_DTX.
> >
> >
> > diff --git a/include/opus_defines.h b/include/opus_defines.h
> > index fbf5d0eb..e35114e4 100644
> > --- a/include/opus_defines.h
> > +++ b/include/opus_defines.h
> > @@ -168,6 +168,7 @@ extern "C" {
> >  /* Don't use 4045, it's already taken by OPUS_GET_GAIN_REQUEST */
> >  #define OPUS_SET_PHASE_INVERSION_DISABLED_REQUEST 4046
> >  #define OPUS_GET_PHASE_INVERSION_DISABLED_REQUEST 4047
> > +#define OPUS_GET_IN_DTX_REQUEST              4049
> >
> >  /** Defines for the presence of extended APIs. */
> >  #define OPUS_HAVE_OPUS_PROJECTION_H
> > @@ -715,6 +716,16 @@ extern "C" {
> >    * </dl>
> >    * @hideinitializer */
> >  #define OPUS_GET_PHASE_INVERSION_DISABLED(x)
> > OPUS_GET_PHASE_INVERSION_DISABLED_REQUEST, __opus_check_int_ptr(x)
> > +/** Gets the DTX state of the encoder.
> > +  * Returns wheter the last encoded frame was either a comfort noise
> update
>
>
> s/wheter/whether/
>
>
> > +  * during DTX or not encoded because of DTX.
> > +  * @param[out] x <tt>opus_int32 *</tt>: Returns one of the following
> > values:
> > +  * <dl>
> > +  * <dt>0</dt><dd>The encoder is not in DTX.</dd>
> > +  * <dt>1</dt><dd>The encoder is in DTX.</dd>
> > +  * </dl>
> > +  * @hideinitializer */
> > +#define OPUS_GET_IN_DTX(x) OPUS_GET_IN_DTX_REQUEST,
> __opus_check_int_ptr(x)
> >
> >  /**@}*/
> >
> > diff --git a/src/opus_encoder.c b/src/opus_encoder.c
> > index cbeb40ae..0d84737a 100644
> > --- a/src/opus_encoder.c
> > +++ b/src/opus_encoder.c
> > @@ -2725,6 +2725,27 @@ int opus_encoder_ctl(OpusEncoder *st, int
> > request, ...)
> >              ret = celt_encoder_ctl(celt_enc,
> OPUS_SET_ENERGY_MASK(value));
> >          }
> >          break;
> > +        case OPUS_GET_IN_DTX_REQUEST:
> > +        {
> > +            opus_int32 *value = va_arg(ap, opus_int32*);
> > +            if (!value)
> > +            {
> > +                goto bad_arg;
> > +            }
> > +            *value = 0;
> > +            if (st->silk_mode.useDTX) {
> > +                /* DTX determined by Silk. */
> > +                void *silk_enc = (char*)st+st->silk_enc_offset;
> > +                *value =
> > ((silk_encoder*)silk_enc)->state_Fxx[0].sCmn.noSpeechCounter >=
> > NB_SPEECH_FRAMES_BEFORE_DTX;
> > +            }
>
>
> It looks like this does not have the same behavior as the code that
> decides whether to produce a DTX frame.  For example, in the case of
> stereo the SILK DTX code considers both channels, but this code looks
> only at state_Fxx[0].  Shouldn't the behavior match?
>
>  - Mark
>
>
>
> > +#ifndef DISABLE_FLOAT_API
> > +            else if (st->use_dtx) {
> > +                /* DTX determined by Opus. */
> > +                *value = st->nb_no_activity_frames >=
> > NB_SPEECH_FRAMES_BEFORE_DTX;
> > +            }
> > +#endif
> > +        }
> > +        break;
> >
> >          case CELT_GET_MODE_REQUEST:
> >          {
> >
> >
>
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