include "sami_core.h"

// help function
std::vector<uint8_t> loadModelAsBinary(const std::string& path) {
   std::ifstream file(path, std::ios::binary | std::ios::ate);
   std::streamsize size = file.tellg();
   file.seekg(0, std::ios::beg);

   std::vector<uint8_t> buffer(size);
   if(file.read((char*)buffer.data(), size)) { return buffer; }

   return {};
}

SAMICoreFeatureArray* findWantedFeature(SAMICoreFeatureSet* f_set, SAMICorePropertyId feature_id) {
   for(int i = 0; i < f_set->numFeatureTypes; ++i) {
       if(f_set->set[i].featureID == feature_id) { return &(f_set->set[i]); }
   }
   return NULL;
}

// step 1, create handle
SAMICoreHandle handle;
SAMICoreExtractorCreateParam param;
param.sampleRate = sample_rate;
param.numChannel = num_channels;

int ret = SAMICoreCreateHandleByIdentify(&handle, SAMICoreIdentify_Extractor_BeatTracking, &param);
assert(ret == SAMI_OK);

// step 2, loading model
const std::string model_path = "/path/to/beat_tracking.model";
std::vector<uint_8> model_buf = loadModelAsBinary(model_path);
assert(model_buf.size() > 0);

SAMICoreProperty coreProperty;
coreProperty.id = SAMICorePropertyId_LoadModelBinary;
coreProperty.data = model_data.data();
coreProperty.dataLen = model_data.size();
coreProperty.type = SAMICoreDataType_ModelBin;
ret = SAMICoreSetProperty(handle, SAMICorePropertyId_LoadModelBinary, &coreProperty);
assert(ret == SAMI_OK);

// step 3, create input  audio block
SAMICoreAudioBuffer in_audio_buffer;
in_audio_buffer.numberChannels = num_channels;
in_audio_buffer.numberSamples = 0;
in_audio_buffer.isInterleave = 0;
in_audio_buffer.data = new float*[num_channels];

SAMICoreBlock in_block;
in_block.dataType = SAMICoreDataType_AudioBuffer;
in_block.numberAudioData = 1;
in_block.audioData = &in_audio_buffer;

// step 4, process bloock by block
for(;hasAudioSamples();)
{
   updateInputBuffer(in_audio_buffer);
   ret = SAMICoreProcess(handle, &in_block, NULL);
   assert(ret == SAMI_OK);

// step 4.1, get beat tracking results
   SAMICoreProperty frame_features;
   SAMICoreGetPropertyById(handle, SAMICorePropertyID_FrameFeatures, &frame_features);
   SAMICoreFeatureSet* feature_set = 
                               (SAMICoreFeatureSet*)(frame_features.data);
   if(feature_set != NULL) 
   {
       SAMICoreFeatureArray* bt_result =
           findWantedFeature(feature_set, SAMICorePropertyID_FrameFeature_BEAT_TRACKING);

       if(bt_result != NULL) {
           float timestamp = bt_result->array[0].time;
           float beat = bt_result->array[0].values[0];

           cout << "time at " << timestamp << ", get beat " << beat << endl;
       }
       SAMICoreDestroyProperty(&frame_features);
   }
}

// step 5, remember release resource
ret = SAMICoreDestroyHandle(handle);
assert(ret == SAMI_OK);

delete[] in_buffer.data;

一、创建算法句柄

传入采样率和声道数，通过 SAMICoreCreateHandleByIdentify 创建 handle。

SAMICoreHandle handle;
SAMICoreExtractorCreateParam param;
param.sampleRate = sample_rate;
param.numChannel = num_channels;

int ret = SAMICoreCreateHandleByIdentify(&handle, SAMICoreIdentify_Extractor_BeatTracking, &param);

二、导入模型

首先读取模型文件到内存，例子中loadModelAsBinary仅供参考；接着，设置模型的信息，并通过SAMICoreSetProperty导入模型

SAMICoreProperty coreProperty;
coreProperty.id = SAMICorePropertyId_LoadModelBinary;
coreProperty.data = model_data.data();
coreProperty.dataLen = model_data.size();
coreProperty.type = SAMICoreDataType_ModelBin;
ret = SAMICoreSetProperty(handle, SAMICorePropertyId_LoadModelBinary, &coreProperty);

三、创建 SAMICoreBlock 用于存放输入和输出

SAMICoreAudioBuffer，用于存放音频数据；SAMICoreBlock，用于存放需要处理的数据。需要注意的是，beat tracking 只处理单声道数据。

SAMICoreAudioBuffer in_buffer;
in_buffer.isInterleave = 0;
in_buffer.numberSamples = 0;
in_buffer.numberChannels = 1;
in_buffer.data = new float*[1];

SAMICoreBlock in_block;
in_block.dataType = SAMICoreDataType_AudioBuffer;
in_block.numberAudioData = 1;
in_block.audioData = &in_buffer;

四、处理音频，并获取结果

更新音频数据的指针，指向正确的内存即可，这样可以避免内存数据的拷贝。

for(;hasAudioSamples();)
{
    in_buffer.data[0] = new_samples_pointer;
    in_buffer.numberSamples = new_samples_length;

    ret = SAMICoreProcess(handle, &in_block, NULL);
    assert(ret == SAMI_OK);

    ....
}

流式 beat tracking 输入是一块一块的音频数据，比如一个 512 大小的音频数据。在调用SAMICoreProcess 后，可以获取当前帧的 beat 结果：

for(;hasAudioSamples();)
{
    // .. process

    // step 4.1, get beat tracking results
    SAMICoreProperty frame_features;
    SAMICoreGetPropertyById(handle, SAMICorePropertyID_FrameFeatures, &frame_features);
    SAMICoreFeatureSet* feature_set = 
                                (SAMICoreFeatureSet*)(frame_features.data);
    if(feature_set != NULL) 
    {
        SAMICoreFeatureArray* bt_result =
            findWantedFeature(feature_set, SAMICorePropertyID_FrameFeature_BEAT_TRACKING);

        if(bt_result != NULL) {
            float timestamp = bt_result->array[0].time;
            float beat = bt_result->array[0].values[0];

            cout << "time at " << timestamp << ", get beat " << beat << endl;
        }
        SAMICoreDestroyProperty(&frame_features);
    }
}

其中：

• 7行，通过SAMICoreGetPropertyById 函数并指定id为SAMICorePropertyID_OverallFeatures，可获取所有算法计算的结果（注：算法可能输出多种类型的特征
• 12 ~ 13 行，通过findWantedFeature 辅助函数找到特征id为SAMICorePropertyID_FrameFeature_BEAT_TRACKING的结果
• 15~20行，获取 beat 的时间戳信息，和节奏信息
• 21 行，记得调用 SAMICoreDestroyProperty 来释放资源

Beat tracking 的输出可能是 1、2、3 或者 4，也就是 强 弱 次强 弱，其中 1 可以认为是重音。下面压缩包中包含一个测试音频、以及对应 beat tracking 结果

五、释放资源

释放 handle

ret = SAMICoreDestroyHandle(handle);

此外，还要注意音频数据数据的内存释放（如果有）。例如：

delete[] in_buffer.data;