static void do_audio_out(AVFormatContext *s, OutputStream *ost,
                         AVFrame *frame)
{
    AVCodecContext *enc = ost->st->codec;
    AVPacket pkt;
    int got_packet = 0;

    av_init_packet(&pkt);
    pkt.data = NULL;
    pkt.size = 0;

    if (!check_recording_time(ost))
        return;

    if (frame->pts == AV_NOPTS_VALUE || audio_sync_method < 0)
        frame->pts = ost->sync_opts;
    ost->sync_opts = frame->pts + frame->nb_samples;

    if (avcodec_encode_audio2(enc, &pkt, frame, &got_packet) < 0) {
        av_log(NULL, AV_LOG_FATAL, "Audio encoding failed\n");
        exit_program(1);
    }

    if (got_packet) {
        if (pkt.pts != AV_NOPTS_VALUE)
            pkt.pts      = av_rescale_q(pkt.pts,      enc->time_base, ost->st->time_base);
        if (pkt.dts != AV_NOPTS_VALUE)
            pkt.dts      = av_rescale_q(pkt.dts,      enc->time_base, ost->st->time_base);
        if (pkt.duration > 0)
            pkt.duration = av_rescale_q(pkt.duration, enc->time_base, ost->st->time_base);

        write_frame(s, &pkt, ost);

        audio_size += pkt.size;
    }
}