C ++ Alsa API记录质量不好

问题描述

我正在尝试在Linux上使用alsa api录制麦克风，但是结果是奇怪的声音，例如冻结的故障机器人。记录通过UDP协议发送到pcm播放器端点的pcm数据。

        char* device = "default";
        unsigned int rate = 44100;
        unsigned int channels = 2;
        snd_pcm_uframes_t frames{};
        snd_pcm_t* capture_handle{};
        snd_pcm_hw_params_t* hw_params{};

        if (snd_pcm_open(&capture_handle,device,SND_PCM_STREAM_CAPTURE,0) < 0)
            throw new std::runtime_error{ "Can't open device for capture" };

        if (snd_pcm_hw_params_malloc(&hw_params) < 0)
            throw new std::runtime_error{ "Can't allocate hw parameters structure" };

        if (snd_pcm_hw_params_any(capture_handle,hw_params) < 0)
            throw new std::runtime_error{ "Can't initialize parameters structure" };

        if (snd_pcm_hw_params_set_access(capture_handle,hw_params,SND_PCM_ACCESS_RW_INTERLEAVED) < 0)
            throw new std::runtime_error{ "Can't set access parameter" };

        if (snd_pcm_hw_params_set_format(capture_handle,SND_PCM_FORMAT_S16_LE) < 0)
            throw new std::runtime_error{ "Can't set access parameter" };

        if (snd_pcm_hw_params_set_rate_near(capture_handle,&rate,0) < 0)
            throw new std::runtime_error{ "Can't set rate" };

        if (snd_pcm_hw_params_set_channels(capture_handle,channels) < 0)
            throw new std::runtime_error{ "Can't set channels count" };

        frames = 32;
        if (snd_pcm_hw_params_set_period_size_near(capture_handle,&frames,0))
            throw new std::runtime_error{ "Can't set period size" };

        if (snd_pcm_hw_params(capture_handle,hw_params) < 0)
            throw new std::runtime_error{ "Can't set parameters" };

        snd_pcm_hw_params_free(hw_params);

        if (snd_pcm_prepare(capture_handle) < 0)
            throw new std::runtime_error{ "Can't prepare capture device" };

        if (snd_pcm_hw_params_get_period_size(hw_params,0) < 0)
            throw new std::runtime_error{ "Can't get frames count" };

        const unsigned int bufSize = frames * channels * 2;
        unsigned int buf[bufSize];
        while (true) {
            if (snd_pcm_readi(capture_handle,&buf[0],bufSize) != bufSize)
                throw new std::runtime_error{ "Can't read from buffer" };
            
            if (connectable != nullptr)
                connectable->sendData(buf,bufSize);
        }

        snd_pcm_close(capture_handle);

抽样结果：https://voca.ro/1m3zDAmdW5cc

解决方法

所以问题是因为我没有指定周期时间，周期大小。在周期操作之后，我需要检索实际值。我在缓冲区大小公式中有错误。固定代码：

...
 frames = periodSize;
        if (snd_pcm_hw_params_set_period_size_near(captureHandle,hwParams,&frames,0) < 0)
            throw new std::runtime_error{ "Can't set period" };

        if (snd_pcm_hw_params_set_period_time_near(captureHandle,const_cast<unsigned int*>(&framesTime),0) < 0)
            throw new std::runtime_error{ "Can't set period time" };
...
snd_pcm_hw_params_get_rate(hwParams,&actualSampleRate,0);

snd_pcm_hw_params_get_period_size(hwParams,0);

snd_pcm_hw_params_get_period_time(hwParams,&actualPeriodTime,0);

snd_pcm_hw_params_get_channels(hwParams,&actualChannels);
...
bufferSize = (frames * channels * snd_pcm_format_physical_width(SND_PCM_FORMAT_S16_LE)) / 8;
...
snd_pcm_readi(captureHandle,buffer,frames);
...
connectable->sendData(buffer,bufferSize);