要加一段代码到一个函数中 c语言写的 不懂加在什么位置 请大看看

if (is_iframe && (s->packet_number % s->pack_header_freq) == 0)
    {
        //find SEQ_START_CODEC
        if(buf[0] == 0x0 && buf[1] == 0x0 && buf[2] == 0x01 && buf[3] != 0xb3)
        {
            if (av_fifo_realloc2(stream->fifo, av_fifo_size(stream->fifo) + size + st->codec->extradata_size) < 0)
                return -1;
            pkt_desc->unwritten_size=
            pkt_desc->size += st->codec->extradata_size;
            av_fifo_generic_write(stream->fifo, st->codec->extradata, st->codec->extradata_size, NULL);
        }
}

需要把上面的判断条件 加到下面的 函数里面 请大们指点

static int mpeg_mux_write_packet(AVFormatContext *ctx, AVPacket *pkt)
{
    int stream_index = pkt->stream_index;
    int size         = pkt->size;
    uint8_t *buf     = pkt->data;
    MpegMuxContext *s = ctx->priv_data;
    AVStream *st      = ctx->streams[stream_index];
    StreamInfo *stream = st->priv_data;
    int64_t pts, dts;
    PacketDesc *pkt_desc;
    int preload;
    const int is_iframe = st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO &&
                          (pkt->flags & AV_PKT_FLAG_KEY);

    preload = av_rescale(s->preload, 90000, AV_TIME_BASE);

    pts = pkt->pts;
    dts = pkt->dts;

    if (s->last_scr == AV_NOPTS_VALUE) {
        if (dts == AV_NOPTS_VALUE || (dts < preload && ctx->avoid_negative_ts) || s->is_dvd) {
            if (dts != AV_NOPTS_VALUE)
                s->preload += av_rescale(-dts, AV_TIME_BASE, 90000);
            s->last_scr = 0;
        } else {
            s->last_scr = dts - preload;
            s->preload = 0;
        }
        preload = av_rescale(s->preload, 90000, AV_TIME_BASE);
        av_log(ctx, AV_LOG_DEBUG, "First SCR: %"PRId64" First DTS: %"PRId64"\n", s->last_scr, dts + preload);
    }

    if (dts != AV_NOPTS_VALUE) dts += preload;
    if (pts != AV_NOPTS_VALUE) pts += preload;

    av_log(ctx, AV_LOG_TRACE, "dts:%f pts:%f flags:%d stream:%d nopts:%d\n",
            dts / 90000.0, pts / 90000.0, pkt->flags,
            pkt->stream_index, pts != AV_NOPTS_VALUE);
    if (!stream->premux_packet)
        stream->next_packet = &stream->premux_packet;
    *stream->next_packet     =
    pkt_desc                 = av_mallocz(sizeof(PacketDesc));
    if (!pkt_desc)
        return AVERROR(ENOMEM);
    pkt_desc->pts            = pts;
    pkt_desc->dts            = dts;
    pkt_desc->unwritten_size =
    pkt_desc->size           = size;
    if (!stream->predecode_packet)
        stream->predecode_packet = pkt_desc;
    stream->next_packet = &pkt_desc->next;

    if (av_fifo_realloc2(stream->fifo, av_fifo_size(stream->fifo) + size) < 0)
        return -1;

    if (s->is_dvd) {
        // min VOBU length 0.4 seconds (mpucoder)
        if (is_iframe &&
            (s->packet_number == 0 ||
             (pts - stream->vobu_start_pts >= 36000))) {
            stream->bytes_to_iframe = av_fifo_size(stream->fifo);
            stream->align_iframe    = 1;
            stream->vobu_start_pts  = pts;
        }
    }

    av_fifo_generic_write(stream->fifo, buf, size, NULL);

    for (;;) {
        int ret = output_packet(ctx, 0);
        if (ret <= 0)
            return ret;
    }
}

第8行怎么半拉代码呢
估计得放到68行吧