AudioTrack:getMinFrameCount代码懂得

static jint android_media_AudioTrack_get_min_buff_size(JNIEnv *env,  jobject thiz,    jint sampleRateInHertz, jint nbChannels, jint audioFormat) {    int frameCount = 0;    if (AudioTrack::getMinFrameCount(&frameCount, AudioSystem::DEFAULT,            sampleRateInHertz) != NO_ERROR) {        return -1;    }    return frameCount * nbChannels * (audioFormat == javaAudioTrackFields.PCM16 ? 2 : 1);// frameCount是如何计算的？}

status_t AudioTrack::getMinFrameCount(        int* frameCount,        int streamType,        uint32_t sampleRate){    int afSampleRate;    if (AudioSystem::getOutputSamplingRate(&afSampleRate, streamType) != NO_ERROR) {        return NO_INIT;    }    int afFrameCount;    if (AudioSystem::getOutputFrameCount(&afFrameCount, streamType) != NO_ERROR) {        return NO_INIT;    }    uint32_t afLatency;    if (AudioSystem::getOutputLatency(&afLatency, streamType) != NO_ERROR) {        return NO_INIT;    }    // Ensure that buffer depth covers at least audio hardware latency    uint32_t minBufCount = afLatency / ((1000 * afFrameCount) / afSampleRate); // 此计算公式如何理解？    if (minBufCount < 2) minBufCount = 2;    *frameCount = (sampleRate == 0) ? afFrameCount * minBufCount :              afFrameCount * minBufCount * sampleRate / afSampleRate; // 此公式又如何理解？    return NO_ERROR;}