mpeg.c

/*
 * MPEG1/2 mux/demux
 * Copyright (c) 2000, 2001, 2002 Fabrice Bellard.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */
#include "avformat.h"
#include "bitstream.h"

#define MAX_PAYLOAD_SIZE 4096
//#define DEBUG_SEEK

#undef NDEBUG
#include <assert.h>

typedef struct PacketDesc {
    int64_t pts;
    int64_t dts;
    int size;
    int unwritten_size;
    int flags;
    struct PacketDesc *next;
} PacketDesc;

typedef struct {
    FifoBuffer fifo;
    uint8_t id;
    int max_buffer_size; /* in bytes */
    int buffer_index;
    PacketDesc *predecode_packet;
    PacketDesc *premux_packet;
    PacketDesc **next_packet;
    int packet_number;
    uint8_t lpcm_header[3];
    int lpcm_align;
    uint8_t *fifo_iframe_ptr;
    int align_iframe;
    int64_t vobu_start_pts;
} StreamInfo;

typedef struct {
    int packet_size; /* required packet size */
    int packet_number;
    int pack_header_freq;     /* frequency (in packets^-1) at which we send pack headers */
    int system_header_freq;
    int system_header_size;
    int mux_rate; /* bitrate in units of 50 bytes/s */
    /* stream info */
    int audio_bound;
    int video_bound;
    int is_mpeg2;
    int is_vcd;
    int is_svcd;
    int is_dvd;
    int64_t last_scr; /* current system clock */

    double vcd_padding_bitrate; //FIXME floats
    int64_t vcd_padding_bytes_written;

} MpegMuxContext;

#define PACK_START_CODE             ((unsigned int)0x000001ba)
#define SYSTEM_HEADER_START_CODE    ((unsigned int)0x000001bb)
#define SEQUENCE_END_CODE           ((unsigned int)0x000001b7)
#define PACKET_START_CODE_MASK      ((unsigned int)0xffffff00)
#define PACKET_START_CODE_PREFIX    ((unsigned int)0x00000100)
#define ISO_11172_END_CODE          ((unsigned int)0x000001b9)

/* mpeg2 */
#define PROGRAM_STREAM_MAP 0x1bc
#define PRIVATE_STREAM_1   0x1bd
#define PADDING_STREAM     0x1be
#define PRIVATE_STREAM_2   0x1bf


#define AUDIO_ID 0xc0
#define VIDEO_ID 0xe0
#define AC3_ID   0x80
#define DTS_ID   0x8a
#define LPCM_ID  0xa0
#define SUB_ID   0x20

#define STREAM_TYPE_VIDEO_MPEG1     0x01
#define STREAM_TYPE_VIDEO_MPEG2     0x02
#define STREAM_TYPE_AUDIO_MPEG1     0x03
#define STREAM_TYPE_AUDIO_MPEG2     0x04
#define STREAM_TYPE_PRIVATE_SECTION 0x05
#define STREAM_TYPE_PRIVATE_DATA    0x06
#define STREAM_TYPE_AUDIO_AAC       0x0f
#define STREAM_TYPE_VIDEO_MPEG4     0x10
#define STREAM_TYPE_VIDEO_H264      0x1b

#define STREAM_TYPE_AUDIO_AC3       0x81
#define STREAM_TYPE_AUDIO_DTS       0x8a

static const int lpcm_freq_tab[4] = { 48000, 96000, 44100, 32000 };

#ifdef CONFIG_MUXERS
static AVOutputFormat mpeg1system_mux;
static AVOutputFormat mpeg1vcd_mux;
static AVOutputFormat mpeg2vob_mux;
static AVOutputFormat mpeg2svcd_mux;
static AVOutputFormat mpeg2dvd_mux;

static int put_pack_header(AVFormatContext *ctx,
                           uint8_t *buf, int64_t timestamp)
{
    MpegMuxContext *s = ctx->priv_data;
    PutBitContext pb;

    init_put_bits(&pb, buf, 128);

    put_bits(&pb, 32, PACK_START_CODE);
    if (s->is_mpeg2) {
        put_bits(&pb, 2, 0x1);
    } else {
        put_bits(&pb, 4, 0x2);
    }
    put_bits(&pb, 3, (uint32_t)((timestamp >> 30) & 0x07));
    put_bits(&pb, 1, 1);
    put_bits(&pb, 15, (uint32_t)((timestamp >> 15) & 0x7fff));
    put_bits(&pb, 1, 1);
    put_bits(&pb, 15, (uint32_t)((timestamp) & 0x7fff));
    put_bits(&pb, 1, 1);
    if (s->is_mpeg2) {
        /* clock extension */
        put_bits(&pb, 9, 0);
    }
    put_bits(&pb, 1, 1);
    put_bits(&pb, 22, s->mux_rate);
    put_bits(&pb, 1, 1);
    if (s->is_mpeg2) {
        put_bits(&pb, 1, 1);
        put_bits(&pb, 5, 0x1f); /* reserved */
        put_bits(&pb, 3, 0); /* stuffing length */
    }
    flush_put_bits(&pb);
    return pbBufPtr(&pb) - pb.buf;
}

static int put_system_header(AVFormatContext *ctx, uint8_t *buf,int only_for_stream_id)
{
    MpegMuxContext *s = ctx->priv_data;
    int size, i, private_stream_coded, id;
    PutBitContext pb;

    init_put_bits(&pb, buf, 128);

    put_bits(&pb, 32, SYSTEM_HEADER_START_CODE);
    put_bits(&pb, 16, 0);
    put_bits(&pb, 1, 1);

    put_bits(&pb, 22, s->mux_rate); /* maximum bit rate of the multiplexed stream */
    put_bits(&pb, 1, 1); /* marker */
    if (s->is_vcd && only_for_stream_id==VIDEO_ID) {
        /* This header applies only to the video stream (see VCD standard p. IV-7)*/
        put_bits(&pb, 6, 0);
    } else
        put_bits(&pb, 6, s->audio_bound);

    if (s->is_vcd) {
        /* see VCD standard, p. IV-7*/
        put_bits(&pb, 1, 0);
        put_bits(&pb, 1, 1);
    } else {
        put_bits(&pb, 1, 0); /* variable bitrate*/
        put_bits(&pb, 1, 0); /* non constrainted bit stream */
    }

    if (s->is_vcd || s->is_dvd) {
        /* see VCD standard p IV-7 */
        put_bits(&pb, 1, 1); /* audio locked */
        put_bits(&pb, 1, 1); /* video locked */
    } else {
        put_bits(&pb, 1, 0); /* audio locked */
        put_bits(&pb, 1, 0); /* video locked */
    }

    put_bits(&pb, 1, 1); /* marker */

    if (s->is_vcd && only_for_stream_id==AUDIO_ID) {
        /* This header applies only to the audio stream (see VCD standard p. IV-7)*/
        put_bits(&pb, 5, 0);
    } else
        put_bits(&pb, 5, s->video_bound);

    if (s->is_dvd) {
        put_bits(&pb, 1, 0);    /* packet_rate_restriction_flag */
        put_bits(&pb, 7, 0x7f); /* reserved byte */
    } else
        put_bits(&pb, 8, 0xff); /* reserved byte */

    /* DVD-Video Stream_bound entries
    id (0xB9) video, maximum P-STD for stream 0xE0. (P-STD_buffer_bound_scale = 1)
    id (0xB8) audio, maximum P-STD for any MPEG audio (0xC0 to 0xC7) streams. If there are none set to 4096 (32x128). (P-STD_buffer_bound_scale = 0)
    id (0xBD) private stream 1 (audio other than MPEG and subpictures). (P-STD_buffer_bound_scale = 1)
    id (0xBF) private stream 2, NAV packs, set to 2x1024. */
    if (s->is_dvd) {

        int P_STD_max_video = 0;
        int P_STD_max_mpeg_audio = 0;
        int P_STD_max_mpeg_PS1 = 0;

        for(i=0;i<ctx->nb_streams;i++) {
            StreamInfo *stream = ctx->streams[i]->priv_data;

            id = stream->id;
            if (id == 0xbd && stream->max_buffer_size > P_STD_max_mpeg_PS1) {
                P_STD_max_mpeg_PS1 = stream->max_buffer_size;
            } else if (id >= 0xc0 && id <= 0xc7 && stream->max_buffer_size > P_STD_max_mpeg_audio) {
                P_STD_max_mpeg_audio = stream->max_buffer_size;
            } else if (id == 0xe0 && stream->max_buffer_size > P_STD_max_video) {
                P_STD_max_video = stream->max_buffer_size;
            }
        }

        /* video */
        put_bits(&pb, 8, 0xb9); /* stream ID */
        put_bits(&pb, 2, 3);
        put_bits(&pb, 1, 1);
        put_bits(&pb, 13, P_STD_max_video / 1024);

        /* audio */
        if (P_STD_max_mpeg_audio == 0)
            P_STD_max_mpeg_audio = 4096;
        put_bits(&pb, 8, 0xb8); /* stream ID */
        put_bits(&pb, 2, 3);
        put_bits(&pb, 1, 0);
        put_bits(&pb, 13, P_STD_max_mpeg_audio / 128);

        /* private stream 1 */
        put_bits(&pb, 8, 0xbd); /* stream ID */
        put_bits(&pb, 2, 3);
        put_bits(&pb, 1, 0);
        put_bits(&pb, 13, P_STD_max_mpeg_PS1 / 128);

        /* private stream 2 */
        put_bits(&pb, 8, 0xbf); /* stream ID */
        put_bits(&pb, 2, 3);
        put_bits(&pb, 1, 1);
        put_bits(&pb, 13, 2);
    }
    else {
        /* audio stream info */
        private_stream_coded = 0;
        for(i=0;i<ctx->nb_streams;i++) {
            StreamInfo *stream = ctx->streams[i]->priv_data;


            /* For VCDs, only include the stream info for the stream
            that the pack which contains this system belongs to.
            (see VCD standard p. IV-7) */
            if ( !s->is_vcd || stream->id==only_for_stream_id
                || only_for_stream_id==0) {

                id = stream->id;
                if (id < 0xc0) {
                    /* special case for private streams (AC3 use that) */
                    if (private_stream_coded)
                        continue;
                    private_stream_coded = 1;
                    id = 0xbd;
                }
                put_bits(&pb, 8, id); /* stream ID */
                put_bits(&pb, 2, 3);
                if (id < 0xe0) {
                    /* audio */
                    put_bits(&pb, 1, 0);
                    put_bits(&pb, 13, stream->max_buffer_size / 128);
                } else {
                    /* video */
                    put_bits(&pb, 1, 1);
                    put_bits(&pb, 13, stream->max_buffer_size / 1024);
                }
            }
        }
    }

    flush_put_bits(&pb);
    size = pbBufPtr(&pb) - pb.buf;
    /* patch packet size */
    buf[4] = (size - 6) >> 8;
    buf[5] = (size - 6) & 0xff;

    return size;
}

static int get_system_header_size(AVFormatContext *ctx)
{
    int buf_index, i, private_stream_coded;
    StreamInfo *stream;
    MpegMuxContext *s = ctx->priv_data;

    if (s->is_dvd)
       return 18; // DVD-Video system headers are 18 bytes fixed length.

    buf_index = 12;
    private_stream_coded = 0;
    for(i=0;i<ctx->nb_streams;i++) {
        stream = ctx->streams[i]->priv_data;
        if (stream->id < 0xc0) {
            if (private_stream_coded)
                continue;
            private_stream_coded = 1;
        }
        buf_index += 3;
    }
    return buf_index;
}

static int mpeg_mux_init(AVFormatContext *ctx)
{
    MpegMuxContext *s = ctx->priv_data;
    int bitrate, i, mpa_id, mpv_id, mps_id, ac3_id, dts_id, lpcm_id, j;
    AVStream *st;
    StreamInfo *stream;
    int audio_bitrate;
    int video_bitrate;

    s->packet_number = 0;
    s->is_vcd = (ctx->oformat == &mpeg1vcd_mux);
    s->is_svcd = (ctx->oformat == &mpeg2svcd_mux);
    s->is_mpeg2 = (ctx->oformat == &mpeg2vob_mux || ctx->oformat == &mpeg2svcd_mux || ctx->oformat == &mpeg2dvd_mux);
    s->is_dvd = (ctx->oformat == &mpeg2dvd_mux);

    if(ctx->packet_size)
        s->packet_size = ctx->packet_size;
    else
        s->packet_size = 2048;

    s->vcd_padding_bytes_written = 0;
    s->vcd_padding_bitrate=0;

    s->audio_bound = 0;
    s->video_bound = 0;
    mpa_id = AUDIO_ID;
    ac3_id = AC3_ID;
    dts_id = DTS_ID;
    mpv_id = VIDEO_ID;
    mps_id = SUB_ID;
    lpcm_id = LPCM_ID;
    for(i=0;i<ctx->nb_streams;i++) {
        st = ctx->streams[i];
        stream = av_mallocz(sizeof(StreamInfo));
        if (!stream)
            goto fail;
        st->priv_data = stream;

        av_set_pts_info(st, 64, 1, 90000);

        switch(st->codec->codec_type) {
        case CODEC_TYPE_AUDIO:
            if (st->codec->codec_id == CODEC_ID_AC3) {
                stream->id = ac3_id++;
            } else if (st->codec->codec_id == CODEC_ID_DTS) {
                stream->id = dts_id++;
            } else if (st->codec->codec_id == CODEC_ID_PCM_S16BE) {
                stream->id = lpcm_id++;
                for(j = 0; j < 4; j++) {
                    if (lpcm_freq_tab[j] == st->codec->sample_rate)
                        break;
                }
                if (j == 4)
                    goto fail;
                if (st->codec->channels > 8)
                    return -1;
                stream->lpcm_header[0] = 0x0c;
                stream->lpcm_header[1] = (st->codec->channels - 1) | (j << 4);
                stream->lpcm_header[2] = 0x80;
                stream->lpcm_align = st->codec->channels * 2;
            } else {
                stream->id = mpa_id++;
            }

            /* This value HAS to be used for VCD (see VCD standard, p. IV-7).
               Right now it is also used for everything else.*/
            stream->max_buffer_size = 4 * 1024;
            s->audio_bound++;
            break;
        case CODEC_TYPE_VIDEO:
            stream->id = mpv_id++;
            if (st->codec->rc_buffer_size)
                stream->max_buffer_size = 6*1024 + st->codec->rc_buffer_size/8;
            else
                stream->max_buffer_size = 230*1024; //FIXME this is probably too small as default
#if 0
                /* see VCD standard, p. IV-7*/
                stream->max_buffer_size = 46 * 1024;
            else
                /* This value HAS to be used for SVCD (see SVCD standard, p. 26 V.2.3.2).
                   Right now it is also used for everything else.*/
                stream->max_buffer_size = 230 * 1024;
#endif
            s->video_bound++;
            break;
        case CODEC_TYPE_SUBTITLE:
            stream->id = mps_id++;
            stream->max_buffer_size = 16 * 1024;
            break;
        default:
            return -1;
        }
        fifo_init(&stream->fifo, 16);
    }
    bitrate = 0;
    audio_bitrate = 0;
    video_bitrate = 0;
    for(i=0;i<ctx->nb_streams;i++) {
        int codec_rate;
        st = ctx->streams[i];
        stream = (StreamInfo*) st->priv_data;

        if(st->codec->rc_max_rate || stream->id==VIDEO_ID)
            codec_rate= st->codec->rc_max_rate;
        else
            codec_rate= st->codec->bit_rate;

        if(!codec_rate)
            codec_rate= (1<<21)*8*50/ctx->nb_streams;

        bitrate += codec_rate;

        if (stream->id==AUDIO_ID)
            audio_bitrate += codec_rate;
        else if (stream->id==VIDEO_ID)
            video_bitrate += codec_rate;
    }

    if(ctx->mux_rate){
        s->mux_rate= (ctx->mux_rate + (8 * 50) - 1) / (8 * 50);
    } else {
        /* we increase slightly the bitrate to take into account the
           headers. XXX: compute it exactly */
        bitrate += bitrate*5/100;
        bitrate += 10000;
        s->mux_rate = (bitrate + (8 * 50) - 1) / (8 * 50);
    }

    if (s->is_vcd) {
        double overhead_rate;

        /* The VCD standard mandates that the mux_rate field is 3528
           (see standard p. IV-6).
           The value is actually "wrong", i.e. if you calculate
           it using the normal formula and the 75 sectors per second transfer
           rate you get a different value because the real pack size is 2324,
           not 2352. But the standard explicitly specifies that the mux_rate
           field in the header must have this value.*/
//        s->mux_rate=2352 * 75 / 50;    /* = 3528*/

        /* The VCD standard states that the muxed stream must be
           exactly 75 packs / second (the data rate of a single speed cdrom).
           Since the video bitrate (probably 1150000 bits/sec) will be below
           the theoretical maximum we have to add some padding packets
           to make up for the lower data rate.
           (cf. VCD standard p. IV-6 )*/

        /* Add the header overhead to the data rate.
           2279 data bytes per audio pack, 2294 data bytes per video pack*/
        overhead_rate = ((audio_bitrate / 8.0) / 2279) * (2324 - 2279);
        overhead_rate += ((video_bitrate / 8.0) / 2294) * (2324 - 2294);
        overhead_rate *= 8;

        /* Add padding so that the full bitrate is 2324*75 bytes/sec */
        s->vcd_padding_bitrate = 2324 * 75 * 8 - (bitrate + overhead_rate);
    }

    if (s->is_vcd || s->is_mpeg2)
        /* every packet */
        s->pack_header_freq = 1;
    else
        /* every 2 seconds */
        s->pack_header_freq = 2 * bitrate / s->packet_size / 8;

    /* the above seems to make pack_header_freq zero sometimes */
    if (s->pack_header_freq == 0)
       s->pack_header_freq = 1;

    if (s->is_mpeg2)
        /* every 200 packets. Need to look at the spec.  */
        s->system_header_freq = s->pack_header_freq * 40;
    else if (s->is_vcd)
        /* the standard mandates that there are only two system headers
           in the whole file: one in the first packet of each stream.
           (see standard p. IV-7 and IV-8) */
        s->system_header_freq = 0x7fffffff;
    else
        s->system_header_freq = s->pack_header_freq * 5;

    for(i=0;i<ctx->nb_streams;i++) {
        stream = ctx->streams[i]->priv_data;
        stream->packet_number = 0;
    }
    s->system_header_size = get_system_header_size(ctx);
    s->last_scr = 0;
    return 0;
 fail:
    for(i=0;i<ctx->nb_streams;i++) {
        av_free(ctx->streams[i]->priv_data);
    }
    return -ENOMEM;
}

static inline void put_timestamp(ByteIOContext *pb, int id, int64_t timestamp)
{
    put_byte(pb,
             (id << 4) |
             (((timestamp >> 30) & 0x07) << 1) |
             1);
    put_be16(pb, (uint16_t)((((timestamp >> 15) & 0x7fff) << 1) | 1));
    put_be16(pb, (uint16_t)((((timestamp) & 0x7fff) << 1) | 1));
}


/* return the number of padding bytes that should be inserted into
   the multiplexed stream.*/
static int get_vcd_padding_size(AVFormatContext *ctx, int64_t pts)
{
    MpegMuxContext *s = ctx->priv_data;
    int pad_bytes = 0;

    if (s->vcd_padding_bitrate > 0 && pts!=AV_NOPTS_VALUE)
    {
        int64_t full_pad_bytes;

        full_pad_bytes = (int64_t)((s->vcd_padding_bitrate * (pts / 90000.0)) / 8.0); //FIXME this is wrong
        pad_bytes = (int) (full_pad_bytes - s->vcd_padding_bytes_written);

        if (pad_bytes<0)
            /* might happen if we have already padded to a later timestamp. This
               can occur if another stream has already advanced further.*/
            pad_bytes=0;
    }

    return pad_bytes;
}


#if 0 /* unused, remove? */
/* return the exact available payload size for the next packet for
   stream 'stream_index'. 'pts' and 'dts' are only used to know if
   timestamps are needed in the packet header. */
static int get_packet_payload_size(AVFormatContext *ctx, int stream_index,
                                   int64_t pts, int64_t dts)
{
    MpegMuxContext *s = ctx->priv_data;
    int buf_index;
    StreamInfo *stream;

    stream = ctx->streams[stream_index]->priv_data;

    buf_index = 0;
    if (((s->packet_number % s->pack_header_freq) == 0)) {
        /* pack header size */
        if (s->is_mpeg2)
            buf_index += 14;
        else
            buf_index += 12;

        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)
                /* The system headers refer only to the stream they occur in,
                   so they have a constant size.*/
                buf_index += 15;

        } else {
            if ((s->packet_number % s->system_header_freq) == 0)
                buf_index += s->system_header_size;
        }
    }

    if ((s->is_vcd && stream->packet_number==0)
        || (s->is_svcd && s->packet_number==0))
        /* the first pack of each stream contains only the pack header,
           the system header and some padding (see VCD standard p. IV-6)
           Add the padding size, so that the actual payload becomes 0.*/
        buf_index += s->packet_size - buf_index;
    else {
        /* packet header size */
        buf_index += 6;
        if (s->is_mpeg2) {
            buf_index += 3;
            if (stream->packet_number==0)
                buf_index += 3; /* PES extension */
            buf_index += 1;    /* obligatory stuffing byte */
        }
        if (pts != AV_NOPTS_VALUE) {
            if (dts != pts)
                buf_index += 5 + 5;
            else
                buf_index += 5;

        } else {
            if (!s->is_mpeg2)
                buf_index++;
        }

        if (stream->id < 0xc0) {
            /* AC3/LPCM private data header */
            buf_index += 4;
            if (stream->id >= 0xa0) {
                int n;
                buf_index += 3;
                /* NOTE: we round the payload size to an integer number of
                   LPCM samples */
                n = (s->packet_size - buf_index) % stream->lpcm_align;
                if (n)
                    buf_index += (stream->lpcm_align - n);
            }
        }

        if (s->is_vcd && stream->id == AUDIO_ID)
            /* The VCD standard demands that 20 zero bytes follow
               each audio packet (see standard p. IV-8).*/
            buf_index+=20;
    }
    return s->packet_size - buf_index;
}
#endif

/* Write an MPEG padding packet header. */
static void put_padding_packet(AVFormatContext *ctx, ByteIOContext *pb,int packet_bytes)
{
    MpegMuxContext *s = ctx->priv_data;
    int i;

    put_be32(pb, PADDING_STREAM);
    put_be16(pb, packet_bytes - 6);
    if (!s->is_mpeg2) {
        put_byte(pb, 0x0f);
        packet_bytes -= 7;
    } else
        packet_bytes -= 6;

    for(i=0;i<packet_bytes;i++)
        put_byte(pb, 0xff);
}

static int get_nb_frames(AVFormatContext *ctx, StreamInfo *stream, int len){
    int nb_frames=0;
    PacketDesc *pkt_desc= stream->premux_packet;

    while(len>0){
        if(pkt_desc->size == pkt_desc->unwritten_size)
            nb_frames++;
        len -= pkt_desc->unwritten_size;
        pkt_desc= pkt_desc->next;
    }

    return nb_frames;
}

/* flush the packet on stream stream_index */
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;

#if 0
    printf("packet ID=%2x PTS=%0.3f\n",
           id, pts / 90000.0);
#endif

    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 bytes_to_iframe;
                int PES_bytes_to_fill;
                if (stream->fifo_iframe_ptr >= stream->fifo.rptr) {
                    bytes_to_iframe = stream->fifo_iframe_ptr - stream->fifo.rptr;
                } else {
                    bytes_to_iframe = (stream->fifo.end - stream->fifo.rptr) + (stream->fifo_iframe_ptr - stream->fifo.buffer);
                }
                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 (bytes_to_iframe == 0 || s->packet_number == 0) {
                    size = put_system_header(ctx, buf_ptr, 0);
                    buf_ptr += size;
                    size = buf_ptr - buffer;
                    put_buffer(&ctx->pb, buffer, size);

                    put_be32(&ctx->pb, PRIVATE_STREAM_2);
                    put_be16(&ctx->pb, 0x03d4);         // length
                    put_byte(&ctx->pb, 0x00);           // substream ID, 00=PCI
                    for (i = 0; i < 979; i++)
                        put_byte(&ctx->pb, 0x00);

                    put_be32(&ctx->pb, PRIVATE_STREAM_2);
                    put_be16(&ctx->pb, 0x03fa);         // length
                    put_byte(&ctx->pb, 0x01);           // substream ID, 01=DSI
                    for (i = 0; i < 1017; i++)
                        put_byte(&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 (bytes_to_iframe < PES_bytes_to_fill) {
                    pad_packet_bytes = PES_bytes_to_fill - 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;
    put_buffer(&ctx->pb, buffer, size);

    packet_size = s->packet_size - size;

    if (s->is_vcd && id == 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 - fifo_size(&stream->fifo, stream->fifo.rptr);

        // first byte doesnt 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);

        put_be32(&ctx->pb, startcode);

        put_be16(&ctx->pb, packet_size);

        if (!s->is_mpeg2)
            for(i=0;i<stuffing_size;i++)
                put_byte(&ctx->pb, 0xff);

        if (s->is_mpeg2) {
            put_byte(&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;

            put_byte(&ctx->pb, pes_flags); /* flags */
            put_byte(&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*/
                put_byte(&ctx->pb, 0x10); /* flags */

                /* P-STD buffer info */
                if (id == AUDIO_ID)
                    put_be16(&ctx->pb, 0x4000 | stream->max_buffer_size/128);
                else
                    put_be16(&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 {
                put_byte(&ctx->pb, 0x0f);
            }
        }

        if (s->is_mpeg2) {
            /* special stuffing byte that is always written
               to prevent accidental generation of start codes. */
            put_byte(&ctx->pb, 0xff);

            for(i=0;i<stuffing_size;i++)
                put_byte(&ctx->pb, 0xff);
        }

        if (startcode == PRIVATE_STREAM_1) {
            put_byte(&ctx->pb, id);
            if (id >= 0xa0) {
                /* LPCM (XXX: check nb_frames) */
                put_byte(&ctx->pb, 7);
                put_be16(&ctx->pb, 4); /* skip 3 header bytes */
                put_byte(&ctx->pb, stream->lpcm_header[0]);
                put_byte(&ctx->pb, stream->lpcm_header[1]);
                put_byte(&ctx->pb, stream->lpcm_header[2]);
            } else if (id >= 0x40) {
                /* AC3 */
                put_byte(&ctx->pb, nb_frames);
                put_be16(&ctx->pb, trailer_size+1);
            }
        }

        /* output data */
        if(put_fifo(&ctx->pb, &stream->fifo, payload_size - stuffing_size, &stream->fifo.rptr) < 0)
            return -1;
    }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++)
        put_byte(&ctx->pb, 0x00);

    put_flush_packet(&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;
}

static void put_vcd_padding_sector(AVFormatContext *ctx)
{
    /* There are two ways to do this padding: writing a sector/pack
       of 0 values, or writing an MPEG padding pack. Both seem to
       work with most decoders, BUT the VCD standard only allows a 0-sector
       (see standard p. IV-4, IV-5).
       So a 0-sector it is...*/

    MpegMuxContext *s = ctx->priv_data;
    int i;

    for(i=0;i<s->packet_size;i++)
        put_byte(&ctx->pb, 0);

    s->vcd_padding_bytes_written += s->packet_size;

    put_flush_packet(&ctx->pb);

    /* increasing the packet number is correct. The SCR of the following packs
       is calculated from the packet_number and it has to include the padding
       sector (it represents the sector index, not the MPEG pack index)