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

[Mark Harris]

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:
>          {
> 
>