unimrcp-voice-activity語音檢測

研究 unimrcp有一段時間了，其中unimrcp voice acitve的算法，是遭到大家頻繁吐槽。今天我們簡單的介紹一下unimrcp voice activity 的這個簡單粗暴的算法：

 

unimrcp 語音活動檢測是通過能量來控制的，設定幾個常量：

struct mpf_activity_detector_t {
/* 靜音檢測閥值 */
apr_size_t level_threshold;

/* 轉換成active狀態的超時時長*/
apr_size_t speech_timeout;
/* 轉換成inactive狀態超時時長 */
apr_size_t silence_timeout;
/* 沒有輸入的超時時長 */
apr_size_t noinput_timeout;

/* 當前的狀態 */
mpf_detector_state_e state;
/* 當前狀態的保持的時長 */
apr_size_t duration;
};

 

來看一下這幾個參數的初始化的值，根據實際的測試，我們后期做過改動：

/** Create activity detector */
MPF_DECLARE(mpf_activity_detector_t*) mpf_activity_detector_create(apr_pool_t *pool)
{
    mpf_activity_detector_t *detector = apr_palloc(pool,sizeof(mpf_activity_detector_t));
    detector->level_threshold = 50; /* 0 .. 255 */
    detector->speech_timeout = 300; /* 0.3 s  = 300*/
    detector->silence_timeout = 1000; /* 0.3 s  =300 */
    detector->noinput_timeout = 5000; /* 5 s =5000*/
    detector->duration = 0;
    detector->state = DETECTOR_STATE_INACTIVITY;
    return detector;
}

 

看一下重要的函數，能量的計算：

根據frame的信息，對能量進行粗暴的累加，所以對於噪音，這個算法完全不可用。后面將會介紹如何采用webrtc的voice active來取代這個算法。

static apr_size_t mpf_activity_detector_level_calculate(const mpf_frame_t *frame)
{
    apr_size_t sum = 0;
    //計算多少個
    apr_size_t count = frame->codec_frame.size/2;
    //初始值
    const apr_int16_t *cur = frame->codec_frame.buffer;
    //最后一個值
    const apr_int16_t *end = cur + count;

    for(; cur < end; cur++) {
        if(*cur < 0) {
            sum -= *cur;
        }
        else {
            sum += *cur;
        }
    }
    //取平均值，簡單粗暴，被吐槽的原因
    return sum / count;
}

 

最后看一下，狀態切換的過程，下面mpf_activity_detector_process函數，主要是通過計算frame的平均值，來完成狀態切換的邏輯：

處理過程共有四個狀態：

      ACTIVITY狀態

      INACTIVITY狀態

     TRANS_ACTIVITY狀態

     TRANS_INACTIVITY狀態

     其中TRANS狀態是中間狀態，再切換為ACTIVITY狀態和INACTIVITY狀態的時，需要經過這個狀態來累計設定時長，如果滿足了，才會切換，否則不予切換。

/** Process current frame */
MPF_DECLARE(mpf_detector_event_e) mpf_activity_detector_process(mpf_activity_detector_t *detector, const mpf_frame_t *frame)
{
    mpf_detector_event_e det_event = MPF_DETECTOR_EVENT_NONE;
    apr_size_t level = 0;
    if((frame->type & MEDIA_FRAME_TYPE_AUDIO) == MEDIA_FRAME_TYPE_AUDIO) {
        /* first, calculate current activity level of processed frame */
        //此處計算得到level的值

        level = mpf_activity_detector_level_calculate(frame);
#if 0
        apt_log(APT_LOG_MARK,APT_PRIO_INFO,"Activity Detector --------------------- [%"APR_SIZE_T_FMT"]",level);
#endif
    }
    /*如果當前狀態處於INACTIVITY狀態，並且level 大於我們設定的閥值，開始向活動狀態切換，但是並沒有變成活動狀態*/
    if(detector->state == DETECTOR_STATE_INACTIVITY) {
        if(level >= detector->level_threshold) {
            /* start to detect activity */
            mpf_activity_detector_state_change(detector,DETECTOR_STATE_ACTIVITY_TRANSITION);
        }
        else {
            detector->duration += CODEC_FRAME_TIME_BASE;
            if(detector->duration >= detector->noinput_timeout) {
                /* detected noinput */
                det_event = MPF_DETECTOR_EVENT_NOINPUT;
            }
        }
    }
    else if(detector->state == DETECTOR_STATE_ACTIVITY_TRANSITION) {
        //處於向活動狀態轉換的過程。
        if(level >= detector->level_threshold) {
            //如果level 大於閥值
            detector->duration += CODEC_FRAME_TIME_BASE;
            //並且超過了設定了向活動狀態轉換的超時時長
            if(detector->duration >= detector->speech_timeout) {
                /* finally detected activity */
                //切換為活動狀態

                det_event = MPF_DETECTOR_EVENT_ACTIVITY;
                mpf_activity_detector_state_change(detector,DETECTOR_STATE_ACTIVITY);
            }
        }
        else {
            /* fallback to inactivity */
            //降級為非活動狀態

            mpf_activity_detector_state_change(detector,DETECTOR_STATE_INACTIVITY);
        }
    }
    else if(detector->state == DETECTOR_STATE_ACTIVITY) {
        //處於活動狀態
        if(level >= detector->level_threshold) {
             //如果level大於閥值，增加duration
            detector->duration += CODEC_FRAME_TIME_BASE;
        }
        else {
            /* start to detect inactivity */
            //准備轉換成inactivity狀態

            mpf_activity_detector_state_change(detector,DETECTOR_STATE_INACTIVITY_TRANSITION);
        }
    }
    else if(detector->state == DETECTOR_STATE_INACTIVITY_TRANSITION) {
        //處於inactivity transtion狀態
        if(level >= detector->level_threshold) {
            /* fallback to activity */
            //如果大於閥值了，則回歸到activity狀態

            mpf_activity_detector_state_change(detector,DETECTOR_STATE_ACTIVITY);
        }
        else {
            //如果檢測仍然小於閥值，增加判斷時長，如果大於設定的時長了，則進入inactivity狀態。
            detector->duration += CODEC_FRAME_TIME_BASE;
            if(detector->duration >= detector->silence_timeout) {
                /* detected inactivity */
                det_event = MPF_DETECTOR_EVENT_INACTIVITY;
                mpf_activity_detector_state_change(detector,DETECTOR_STATE_INACTIVITY);
            }
        }
    }

    return det_event;
}