// вызов
while (seek_pos < data_size) {
    read = fread(&buff, 1, buff_size, fp);
    // ...
    for (pos = 0; pos < read; pos++, seek_pos++) {
        // ...
        if (mpeg_parse_frame(buff + pos, &header)) {

            // ... сохраняем значения в индекс

            pos += header.frame_size;
            seek_pos += header.frame_size;
        }
    }
}




// реализация
static unsigned
mpeg_parse_frame(
    const unsigned char *buff,
    mpeg_header_t *const header
)
{
    unsigned  header_bitrate;
    unsigned  header_samplerate;
    char     *xing;

    // check sync
    if (buff[0] != 0xff || buff[1] < 0xe0) {
        return 0;
    }
    // get and check version
    switch (buff[1] >> 3 & 0x03) {
        case 3: // MPEG Version 1
            header->version = 0;
        break;
        case 2: // MPEG Version 2
            header->version = 1;
        break;
        case 0: // MPEG Version 2.5
            header->version = 2;
        break;
        default:
            return 0;
        break;
    }
    // get and check layer
    header->layer = 3 - (buff[1] >> 1 & 0x03);
    if (header->layer == 3) {
        return 0;
    }
    // get and check bitrate
    header_bitrate = buff[2] >> 4;
    if (header_bitrate == 0x0f) {
        return 0;
    }
    // get and check samplerate
    header_samplerate = buff[2] >> 2 & 0x03;
    if (header_samplerate == 0x03) {
        return 0;
    }
    // get bitrate value
    if (header->version == 1) {
        header->bitrate = mpeg_kbps[1][header->layer][header_bitrate];
    } else {
        header->bitrate = mpeg_kbps[0][header->layer][header_bitrate];
    }
    if (!header->bitrate) {
        return 0;
    }
    // get samplerate value
    header->samplerate = mpeg_freq[header->version][header_samplerate];
    // get number of PCM samples
    header->samples = mpeg_pcm_samples[header->version][header->layer];
    // get padding bit
    header->padding_bit = buff[2] >> 1 & 0x01;
    // get channel mode
    header->mode = buff[3] >> 6 & 0x03;
    // get VBR
    header->vbr = 0; // none
    xing = (char *) (buff + (
        !header->version
            ? (header->mode < 3 ? 32 : 17) // MPEG-1
            : (header->mode < 3 ? 17 :  9) // MPEG-2 LSF, MPEG-2.5
    ));
    if (!strncmp(xing, "Xing", 4) || !strncmp(xing, "Info", 4)) {
        header->vbr = 1; // xing
    } else if (!strncmp((char *) (buff + 32), "VBRI", 4)) {
        header->vbr = 2; // vbri
    }

    // TODO frame size for VBR is incorrect
    if (!header->layer) {
        header->frame_size = (size_t) (((12000 * header->bitrate / header->samplerate) + header->padding_bit) * 4);
    } else {
        header->frame_size = (size_t) ((144000 * header->bitrate / header->samplerate) + header->padding_bit);
    }
    if (!header->frame_size) {
        //return 0; TODO free format
    }

    return 1;
}