static int flush_packet(AVFormatContext *ctx, int stream_index,
                         int64_t pts, int64_t dts, int64_t scr, int trailer_size)
{
    MpegMuxContext *s = ctx->priv_data;
    StreamInfo *stream = ctx->streams[stream_index]->priv_data;
    uint8_t *buf_ptr;
    int size, payload_size, startcode, id, stuffing_size, i, header_len;
    int packet_size;
    uint8_t buffer[128];
    int zero_trail_bytes = 0;
    int pad_packet_bytes = 0;
    int pes_flags;
    int general_pack = 0;  /*"general" pack without data specific to one stream?*/
    int nb_frames;
    id = stream->id;
    av_dlog(ctx, "packet ID=%2x PTS=%0.3f\n", id, pts / 90000.0);
    buf_ptr = buffer;
    if ((s->packet_number % s->pack_header_freq) == 0 || s->last_scr != scr) {
        /* output pack and systems header if needed */
        size = put_pack_header(ctx, buf_ptr, scr);
        buf_ptr += size;
        s->last_scr= scr;
        if (s->is_vcd) {
            /* there is exactly one system header for each stream in a VCD MPEG,
               One in the very first video packet and one in the very first
               audio packet (see VCD standard p. IV-7 and IV-8).*/
            if (stream->packet_number==0) {
                size = put_system_header(ctx, buf_ptr, id);
                buf_ptr += size;
        } else if (s->is_dvd) {
            if (stream->align_iframe || s->packet_number == 0){
                int PES_bytes_to_fill = s->packet_size - size - 10;
                if (pts != AV_NOPTS_VALUE) {
                    if (dts != pts)
                        PES_bytes_to_fill -= 5 + 5;
                    else
                        PES_bytes_to_fill -= 5;
                if (stream->bytes_to_iframe == 0 || s->packet_number == 0) {
                    size = put_system_header(ctx, buf_ptr, 0);
                    buf_ptr += size;
                    size = buf_ptr - buffer;
                    avio_write(ctx->pb, buffer, size);
                    avio_wb32(ctx->pb, PRIVATE_STREAM_2);
                    avio_wb16(ctx->pb, 0x03d4);         // length
                    avio_w8(ctx->pb, 0x00);           // substream ID, 00=PCI
                    for (i = 0; i < 979; i++)
                        avio_w8(ctx->pb, 0x00);
                    avio_wb32(ctx->pb, PRIVATE_STREAM_2);
                    avio_wb16(ctx->pb, 0x03fa);         // length
                    avio_w8(ctx->pb, 0x01);           // substream ID, 01=DSI
                    for (i = 0; i < 1017; i++)
                        avio_w8(ctx->pb, 0x00);
                    memset(buffer, 0, 128);
                    buf_ptr = buffer;
                    s->packet_number++;
                    stream->align_iframe = 0;
                    scr += s->packet_size*90000LL / (s->mux_rate*50LL); //FIXME rounding and first few bytes of each packet
                    size = put_pack_header(ctx, buf_ptr, scr);
                    s->last_scr= scr;
                    buf_ptr += size;
                    /* GOP Start */
                } else if (stream->bytes_to_iframe < PES_bytes_to_fill) {
                    pad_packet_bytes = PES_bytes_to_fill - stream->bytes_to_iframe;
        } else {
            if ((s->packet_number % s->system_header_freq) == 0) {
                size = put_system_header(ctx, buf_ptr, 0);
                buf_ptr += size;
    size = buf_ptr - buffer;
    avio_write(ctx->pb, buffer, size);
    packet_size = s->packet_size - size;
    if (s->is_vcd && (id & 0xe0) == AUDIO_ID)
        /* The VCD standard demands that 20 zero bytes follow
           each audio pack (see standard p. IV-8).*/
        zero_trail_bytes += 20;
    if ((s->is_vcd && stream->packet_number==0)
        || (s->is_svcd && s->packet_number==0)) {
        /* for VCD the first pack of each stream contains only the pack header,
           the system header and lots of padding (see VCD standard p. IV-6).
           In the case of an audio pack, 20 zero bytes are also added at
           the end.*/
        /* For SVCD we fill the very first pack to increase compatibility with
           some DVD players. Not mandated by the standard.*/
        if (s->is_svcd)
            general_pack = 1;    /* the system header refers to both streams and no stream data*/
        pad_packet_bytes = packet_size - zero_trail_bytes;
    packet_size -= pad_packet_bytes + zero_trail_bytes;
    if (packet_size > 0) {
        /* packet header size */
        packet_size -= 6;
        /* packet header */
        if (s->is_mpeg2) {
            header_len = 3;
            if (stream->packet_number==0)
                header_len += 3; /* PES extension */
            header_len += 1; /* obligatory stuffing byte */
        } else {
            header_len = 0;
        if (pts != AV_NOPTS_VALUE) {
            if (dts != pts)
                header_len += 5 + 5;
            else
                header_len += 5;
        } else {
            if (!s->is_mpeg2)
                header_len++;
        payload_size = packet_size - header_len;
        if (id < 0xc0) {
            startcode = PRIVATE_STREAM_1;
            payload_size -= 1;
            if (id >= 0x40) {
                payload_size -= 3;
                if (id >= 0xa0)
                    payload_size -= 3;
        } else {
            startcode = 0x100 + id;
        stuffing_size = payload_size - av_fifo_size(stream->fifo);
        // first byte does not fit -> reset pts/dts + stuffing
        if(payload_size <= trailer_size && pts != AV_NOPTS_VALUE){
            int timestamp_len=0;
            if(dts != pts)
                timestamp_len += 5;
            if(pts != AV_NOPTS_VALUE)
                timestamp_len += s->is_mpeg2 ? 5 : 4;
            pts=dts= AV_NOPTS_VALUE;
            header_len -= timestamp_len;
            if (s->is_dvd && stream->align_iframe) {
                pad_packet_bytes += timestamp_len;
                packet_size  -= timestamp_len;
            } else {
                payload_size += timestamp_len;
            stuffing_size += timestamp_len;
            if(payload_size > trailer_size)
                stuffing_size += payload_size - trailer_size;
        if (pad_packet_bytes > 0 && pad_packet_bytes <= 7) { // can't use padding, so use stuffing
            packet_size += pad_packet_bytes;
            payload_size += pad_packet_bytes; // undo the previous adjustment
            if (stuffing_size < 0) {
                stuffing_size  = pad_packet_bytes;
            } else {
                stuffing_size += pad_packet_bytes;
            pad_packet_bytes = 0;
        if (stuffing_size < 0)
            stuffing_size = 0;
        if (stuffing_size > 16) {    /*<=16 for MPEG-1, <=32 for MPEG-2*/
            pad_packet_bytes += stuffing_size;
            packet_size      -= stuffing_size;
            payload_size     -= stuffing_size;
            stuffing_size = 0;
        nb_frames= get_nb_frames(ctx, stream, payload_size - stuffing_size);
        avio_wb32(ctx->pb, startcode);
        avio_wb16(ctx->pb, packet_size);
        if (!s->is_mpeg2)
            for(i=0;i<stuffing_size;i++)
                avio_w8(ctx->pb, 0xff);
        if (s->is_mpeg2) {
            avio_w8(ctx->pb, 0x80); /* mpeg2 id */
            pes_flags=0;
            if (pts != AV_NOPTS_VALUE) {
                pes_flags |= 0x80;
                if (dts != pts)
                    pes_flags |= 0x40;
            /* Both the MPEG-2 and the SVCD standards demand that the
               P-STD_buffer_size field be included in the first packet of
               every stream. (see SVCD standard p. 26 V.2.3.1 and V.2.3.2
               and MPEG-2 standard 2.7.7) */
            if (stream->packet_number == 0)
                pes_flags |= 0x01;
            avio_w8(ctx->pb, pes_flags); /* flags */
            avio_w8(ctx->pb, header_len - 3 + stuffing_size);
            if (pes_flags & 0x80)  /*write pts*/
                put_timestamp(ctx->pb, (pes_flags & 0x40) ? 0x03 : 0x02, pts);
            if (pes_flags & 0x40)  /*write dts*/
                put_timestamp(ctx->pb, 0x01, dts);
            if (pes_flags & 0x01) {  /*write pes extension*/
                avio_w8(ctx->pb, 0x10); /* flags */
                /* P-STD buffer info */
                if ((id & 0xe0) == AUDIO_ID)
                    avio_wb16(ctx->pb, 0x4000 | stream->max_buffer_size/ 128);
                else
                    avio_wb16(ctx->pb, 0x6000 | stream->max_buffer_size/1024);
        } else {
            if (pts != AV_NOPTS_VALUE) {
                if (dts != pts) {
                    put_timestamp(ctx->pb, 0x03, pts);
                    put_timestamp(ctx->pb, 0x01, dts);
                } else {
                    put_timestamp(ctx->pb, 0x02, pts);
            } else {
                avio_w8(ctx->pb, 0x0f);
        if (s->is_mpeg2) {
            /* special stuffing byte that is always written
               to prevent accidental generation of start codes. */
            avio_w8(ctx->pb, 0xff);
            for(i=0;i<stuffing_size;i++)
                avio_w8(ctx->pb, 0xff);
        if (startcode == PRIVATE_STREAM_1) {
            avio_w8(ctx->pb, id);
            if (id >= 0xa0) {
                /* LPCM (XXX: check nb_frames) */
                avio_w8(ctx->pb, 7);
                avio_wb16(ctx->pb, 4); /* skip 3 header bytes */
                avio_w8(ctx->pb, stream->lpcm_header[0]);
                avio_w8(ctx->pb, stream->lpcm_header[1]);
                avio_w8(ctx->pb, stream->lpcm_header[2]);
            } else if (id >= 0x40) {
                /* AC-3 */
                avio_w8(ctx->pb, nb_frames);
                avio_wb16(ctx->pb, trailer_size+1);
        /* output data */
        assert(payload_size - stuffing_size <= av_fifo_size(stream->fifo));
        av_fifo_generic_read(stream->fifo, ctx->pb, payload_size - stuffing_size, &avio_write);
        stream->bytes_to_iframe -= payload_size - stuffing_size;
    }else{
        payload_size=
        stuffing_size= 0;
    if (pad_packet_bytes > 0)
        put_padding_packet(ctx,ctx->pb, pad_packet_bytes);
    for(i=0;i<zero_trail_bytes;i++)
        avio_w8(ctx->pb, 0x00);
    avio_flush(ctx->pb);
    s->packet_number++;
    /* only increase the stream packet number if this pack actually contains
       something that is specific to this stream! I.e. a dedicated header
       or some data.*/
    if (!general_pack)
        stream->packet_number++;
    return payload_size - stuffing_size;