[RK 3288][Android 6.0]Tinycap録音プログラムソースコードの概要

Platform: Rockchip OS: Android 6.0
Kernel: 3.10.92
ソースコードはexternal/tinyalsa/tinycapにあります.c

int main(int argc, char **argv)
{
    FILE *file;
    struct wav_header header;
    //           ，   ，44.1kHz   ，16bit
    //period 1024 ,count  4 。
    unsigned int card = 0;
    unsigned int device = 0;
    unsigned int channels = 2;
    unsigned int rate = 44100;
    unsigned int bits = 16;
    unsigned int frames;
    unsigned int period_size = 1024;
    unsigned int period_count = 4;
    enum pcm_format format;


	//          。
    file = fopen(argv[1], "wb");
    if (!file) {
        fprintf(stderr, "Unable to create file '%s'
", argv[1]);
        return 1;
    }
	//           
    argv += 2;
    while (*argv) {
        if (strcmp(*argv, "-d") == 0) {
            argv++;
            if (*argv)
                device = atoi(*argv);
      ......
    }
	//wav         
    header.riff_id = ID_RIFF;
    header.riff_sz = 0;
    header.riff_fmt = ID_WAVE;
    header.fmt_id = ID_FMT;
    header.fmt_sz = 16;
    header.audio_format = FORMAT_PCM;
    header.num_channels = channels;
    header.sample_rate = rate;
......
    /* leave enough room for header */
    fseek(file, sizeof(struct wav_header), SEEK_SET);
......
    frames = capture_sample(file, card, device, header.num_channels,
                            header.sample_rate, format,
                            period_size, period_count);
......
    //   wav header   。
    fwrite(&header, sizeof(struct wav_header), 1, file);
    fclose(file);
    return 0;
}

capture_sample():

unsigned int capture_sample(FILE *file, unsigned int card, unsigned int device,
                            unsigned int channels, unsigned int rate,
                            enum pcm_format format, unsigned int period_size,
                            unsigned int period_count)
{
    struct pcm_config config;
......
	//   config
    config.channels = channels;
    config.rate = rate;
    config.period_size = period_size;
    config.period_count = period_count;
    config.format = format;
    config.start_threshold = 0;
    config.stop_threshold = 0;
    config.silence_threshold = 0;
	//  tinyalsa    
    pcm = pcm_open(card, device, PCM_IN, &config);
    if (!pcm || !pcm_is_ready(pcm)) {
        fprintf(stderr, "Unable to open PCM device (%s)
",
                pcm_get_error(pcm));
        return 0;
    }
	//      frame，       size.
    size = pcm_frames_to_bytes(pcm, pcm_get_buffer_size(pcm));
    buffer = malloc(size);
......
	//    size    。
    while (capturing && !pcm_read(pcm, buffer, size)) {
		//    
        if (fwrite(buffer, 1, size, file) != size) {
            fprintf(stderr,"Error capturing sample
");
            break;
        }
		//       
        bytes_read += size;
    }
......
	//          
    return pcm_bytes_to_frames(pcm, bytes_read);
}

全体の流れは比較的簡単で、コア部分は主にpcm_Open()およびpcm_read()興味があれば検討してください.
でも注意したいのはperoid_sizeとperoid_countには範囲があり、どんな数値でもいいわけではないが、frame rateは固定で44.1 kHzである.