static int encode_init(AVCodecContext * avctx){
    WMACodecContext *s = avctx->priv_data;
    int i, flags1, flags2;
    uint8_t *extradata;

    s->avctx = avctx;

    if(avctx->channels > MAX_CHANNELS) {
        av_log(avctx, AV_LOG_ERROR, "too many channels: got %i, need %i or fewer",
               avctx->channels, MAX_CHANNELS);
        return AVERROR(EINVAL);
    }

    if (avctx->sample_rate > 48000) {
        av_log(avctx, AV_LOG_ERROR, "sample rate is too high: %d > 48kHz",
               avctx->sample_rate);
        return AVERROR(EINVAL);
    }

    if(avctx->bit_rate < 24*1000) {
        av_log(avctx, AV_LOG_ERROR, "bitrate too low: got %i, need 24000 or higher\n",
               avctx->bit_rate);
        return AVERROR(EINVAL);
    }

    /* extract flag infos */
    flags1 = 0;
    flags2 = 1;
    if (avctx->codec->id == CODEC_ID_WMAV1) {
        extradata= av_malloc(4);
        avctx->extradata_size= 4;
        AV_WL16(extradata, flags1);
        AV_WL16(extradata+2, flags2);
    } else if (avctx->codec->id == CODEC_ID_WMAV2) {
        extradata= av_mallocz(10);
        avctx->extradata_size= 10;
        AV_WL32(extradata, flags1);
        AV_WL16(extradata+4, flags2);
    }else
        av_assert0(0);
    avctx->extradata= extradata;
    s->use_exp_vlc = flags2 & 0x0001;
    s->use_bit_reservoir = flags2 & 0x0002;
    s->use_variable_block_len = flags2 & 0x0004;
    if (avctx->channels == 2)
        s->ms_stereo = 1;

    ff_wma_init(avctx, flags2);

    /* init MDCT */
    for(i = 0; i < s->nb_block_sizes; i++)
        ff_mdct_init(&s->mdct_ctx[i], s->frame_len_bits - i + 1, 0, 1.0);

    s->block_align     = avctx->bit_rate * (int64_t)s->frame_len /
                         (avctx->sample_rate * 8);
    s->block_align     = FFMIN(s->block_align, MAX_CODED_SUPERFRAME_SIZE);
    avctx->block_align = s->block_align;
//av_log(NULL, AV_LOG_ERROR, "%d %d %d %d\n", s->block_align, avctx->bit_rate, s->frame_len, avctx->sample_rate);
    avctx->frame_size = avctx->delay = s->frame_len;

#if FF_API_OLD_ENCODE_AUDIO
    avctx->coded_frame = &s->frame;
    avcodec_get_frame_defaults(avctx->coded_frame);
#endif

    return 0;
}