FFmpeg/libavformat/mpegenc.c

/*
 * MPEG1/2 muxer
 * Copyright (c) 2000, 2001, 2002 Fabrice Bellard
 *
 * This file is part of Libav.
 *
 * Libav 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 2.1 of the License, or (at your option) any later version.
 *
 * Libav 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 Libav; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include <stdint.h>

#include "libavutil/attributes.h"
#include "libavutil/fifo.h"
#include "libavutil/log.h"
#include "libavutil/mathematics.h"
#include "libavutil/opt.h"

#include "libavcodec/put_bits.h"

#include "avformat.h"
#include "internal.h"
#include "mpeg.h"

#define MAX_PAYLOAD_SIZE 4096

#undef NDEBUG
#include <assert.h>

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

typedef struct {
    AVFifoBuffer *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;
    int bytes_to_iframe;
    int align_iframe;
    int64_t vobu_start_pts;
} StreamInfo;

typedef struct {
    const AVClass *class;
    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;

    int preload;
} MpegMuxContext;

extern AVOutputFormat ff_mpeg1vcd_muxer;
extern AVOutputFormat ff_mpeg2dvd_muxer;
extern AVOutputFormat ff_mpeg2svcd_muxer;
extern AVOutputFormat ff_mpeg2vob_muxer;

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_bits32(&pb, 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 put_bits_ptr(&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_bits32(&pb, SYSTEM_HEADER_START_CODE);
    put_bits(&pb, 16, 0);
    put_bits(&pb, 1, 1);

    /* maximum bit rate of the multiplexed stream */
    put_bits(&pb, 22, s->mux_rate);
    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 & 0xe0) == 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 (AC-3 uses 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 = put_bits_ptr(&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 av_cold int mpeg_mux_init(AVFormatContext *ctx)
{
    MpegMuxContext *s = ctx->priv_data;
    int bitrate, i, mpa_id, mpv_id, h264_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   =  (CONFIG_MPEG1VCD_MUXER  && ctx->oformat == &ff_mpeg1vcd_muxer);
    s->is_svcd  =  (CONFIG_MPEG2SVCD_MUXER && ctx->oformat == &ff_mpeg2svcd_muxer);
    s->is_mpeg2 = ((CONFIG_MPEG2VOB_MUXER  && ctx->oformat == &ff_mpeg2vob_muxer) ||
                   (CONFIG_MPEG2DVD_MUXER  && ctx->oformat == &ff_mpeg2dvd_muxer) ||
                   (CONFIG_MPEG2SVCD_MUXER && ctx->oformat == &ff_mpeg2svcd_muxer));
    s->is_dvd   =  (CONFIG_MPEG2DVD_MUXER  && ctx->oformat == &ff_mpeg2dvd_muxer);

    if (ctx->packet_size) {
        if (ctx->packet_size < 20 || ctx->packet_size > (1 << 23) + 10) {
            av_log(ctx, AV_LOG_ERROR, "Invalid packet size %d\n",
                   ctx->packet_size);
            goto fail;
        }
        s->packet_size = ctx->packet_size;
    } else
        s->packet_size = 2048;
    if (ctx->max_delay < 0)     /* Not set by the caller */
        ctx->max_delay = 0;

    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;
    h264_id = H264_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;

        avpriv_set_pts_info(st, 64, 1, 90000);

        switch (st->codec->codec_type) {
        case AVMEDIA_TYPE_AUDIO:
            if (st->codec->codec_id == AV_CODEC_ID_AC3) {
                stream->id = ac3_id++;
            } else if (st->codec->codec_id == AV_CODEC_ID_DTS) {
                stream->id = dts_id++;
            } else if (st->codec->codec_id == AV_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 AVMEDIA_TYPE_VIDEO:
            if (st->codec->codec_id == AV_CODEC_ID_H264)
                stream->id = h264_id++;
            else
                stream->id = mpv_id++;
            if (st->codec->rc_buffer_size)
                stream->max_buffer_size = 6 * 1024 + st->codec->rc_buffer_size / 8;
            else {
                av_log(ctx, AV_LOG_WARNING,
                       "VBV buffer size not set, muxing may fail\n");
                // FIXME: this is probably too small as default
                stream->max_buffer_size = 230 * 1024;
            }
            s->video_bound++;
            break;
        case AVMEDIA_TYPE_SUBTITLE:
            stream->id              = mps_id++;
            stream->max_buffer_size = 16 * 1024;
            break;
        default:
            return -1;
        }
        stream->fifo = av_fifo_alloc(16);
        if (!stream->fifo)
            goto fail;
    }
    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 ||
            st->codec->codec_type == AVMEDIA_TYPE_VIDEO)
            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 & 0xe0) == AUDIO_ID)
            audio_bitrate += codec_rate;
        else if (st->codec->codec_type == AVMEDIA_TYPE_VIDEO)
            video_bitrate += codec_rate;
    }

    if (!s->mux_rate) {
        /* we increase slightly the bitrate to take into account the
         * headers. XXX: compute it exactly */
        bitrate    += bitrate / 20;
        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 AVERROR(ENOMEM);
}

static inline void put_timestamp(AVIOContext *pb, int id, int64_t timestamp)
{
    avio_w8(pb, (id << 4) |  (((timestamp >> 30) & 0x07)   << 1) | 1);
    avio_wb16(pb, (uint16_t)((((timestamp >> 15) & 0x7fff) << 1) | 1));
    avio_wb16(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;

        // FIXME: this is wrong
        full_pad_bytes =
            (int64_t)((s->vcd_padding_bitrate * (pts / 90000.0)) / 8.0);
        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;
}

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

    avio_wb32(pb, PADDING_STREAM);
    avio_wb16(pb, packet_bytes - 6);
    if (!s->is_mpeg2) {
        avio_w8(pb, 0x0f);
        packet_bytes -= 7;
    } else
        packet_bytes -= 6;

    for (i = 0; i < packet_bytes; i++)
        avio_w8(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;
    /* "general" pack without data specific to one stream? */
    int general_pack = 0;
    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;
                    // FIXME: rounding and first few bytes of each packet
                    scr        += s->packet_size * 90000LL /
                                  (s->mux_rate * 50LL);
                    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)
            /* the system header refers to both streams and no stream data */
            general_pack = 1;
        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;
        }

        // can't use padding, so use stuffing
        if (pad_packet_bytes > 0 && pad_packet_bytes <= 7) {
            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 (startcode == PRIVATE_STREAM_1 && id >= 0xa0) {
            if (payload_size < av_fifo_size(stream->fifo))
                stuffing_size += payload_size % stream->lpcm_align;
        }

        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,
                             (void (*)(void*, void*, int))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;
}

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++)
        avio_w8(ctx->pb, 0);

    s->vcd_padding_bytes_written += s->packet_size;

    avio_flush(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)
     * (see VCD standard p. IV-6) */
    s->packet_number++;
}

static int remove_decoded_packets(AVFormatContext *ctx, int64_t scr)
{
    int i;

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

        while ((pkt_desc = stream->predecode_packet) &&
               scr > pkt_desc->dts) { // FIXME: > vs >=
            if (stream->buffer_index < pkt_desc->size ||
                stream->predecode_packet == stream->premux_packet) {
                av_log(ctx, AV_LOG_ERROR,
                       "buffer underflow i=%d bufi=%d size=%d\n",
                       i, stream->buffer_index, pkt_desc->size);
                break;
            }
            stream->buffer_index    -= pkt_desc->size;
            stream->predecode_packet = pkt_desc->next;
            av_freep(&pkt_desc);
        }
    }

    return 0;
}

static int output_packet(AVFormatContext *ctx, int flush)
{
    MpegMuxContext *s = ctx->priv_data;
    AVStream *st;
    StreamInfo *stream;
    int i, avail_space = 0, es_size, trailer_size;
    int best_i = -1;
    int best_score = INT_MIN;
    int ignore_constraints = 0;
    int64_t scr = s->last_scr;
    PacketDesc *timestamp_packet;
    const int64_t max_delay = av_rescale(ctx->max_delay, 90000, AV_TIME_BASE);

retry:
    for (i = 0; i < ctx->nb_streams; i++) {
        AVStream *st = ctx->streams[i];
        StreamInfo *stream = st->priv_data;
        const int avail_data = av_fifo_size(stream->fifo);
        const int space = stream->max_buffer_size - stream->buffer_index;
        int rel_space = 1024 * space / stream->max_buffer_size;
        PacketDesc *next_pkt = stream->premux_packet;

        /* for subtitle, a single PES packet must be generated,
         * so we flush after every single subtitle packet */
        if (s->packet_size > avail_data && !flush
            && st->codec->codec_type != AVMEDIA_TYPE_SUBTITLE)
            return 0;
        if (avail_data == 0)
            continue;
        assert(avail_data > 0);

        if (space < s->packet_size && !ignore_constraints)
            continue;

        if (next_pkt && next_pkt->dts - scr > max_delay)
            continue;

        if (rel_space > best_score) {
            best_score  = rel_space;
            best_i      = i;
            avail_space = space;
        }
    }

    if (best_i < 0) {
        int64_t best_dts = INT64_MAX;

        for (i = 0; i < ctx->nb_streams; i++) {
            AVStream *st = ctx->streams[i];
            StreamInfo *stream = st->priv_data;
            PacketDesc *pkt_desc = stream->predecode_packet;
            if (pkt_desc && pkt_desc->dts < best_dts)
                best_dts = pkt_desc->dts;
        }

        av_dlog(ctx, "bumping scr, scr:%f, dts:%f\n",
                scr / 90000.0, best_dts / 90000.0);
        if (best_dts == INT64_MAX)
            return 0;

        if (scr >= best_dts + 1 && !ignore_constraints) {
            av_log(ctx, AV_LOG_ERROR,
                   "packet too large, ignoring buffer limits to mux it\n");
            ignore_constraints = 1;
        }
        scr = FFMAX(best_dts + 1, scr);
        if (remove_decoded_packets(ctx, scr) < 0)
            return -1;
        goto retry;
    }

    assert(best_i >= 0);

    st     = ctx->streams[best_i];
    stream = st->priv_data;

    assert(av_fifo_size(stream->fifo) > 0);

    assert(avail_space >= s->packet_size || ignore_constraints);

    timestamp_packet = stream->premux_packet;
    if (timestamp_packet->unwritten_size == timestamp_packet->size) {
        trailer_size = 0;
    } else {
        trailer_size     = timestamp_packet->unwritten_size;
        timestamp_packet = timestamp_packet->next;
    }

    if (timestamp_packet) {
        av_dlog(ctx, "dts:%f pts:%f scr:%f stream:%d\n",
                timestamp_packet->dts / 90000.0,
                timestamp_packet->pts / 90000.0,
                scr / 90000.0, best_i);
        es_size = flush_packet(ctx, best_i, timestamp_packet->pts,
                               timestamp_packet->dts, scr, trailer_size);
    } else {
        assert(av_fifo_size(stream->fifo) == trailer_size);
        es_size = flush_packet(ctx, best_i, AV_NOPTS_VALUE, AV_NOPTS_VALUE, scr,
                               trailer_size);
    }

    if (s->is_vcd) {
        /* Write one or more padding sectors, if necessary, to reach
         * the constant overall bitrate. */
        int vcd_pad_bytes;

        // FIXME: pts cannot be correct here
        while ((vcd_pad_bytes = get_vcd_padding_size(ctx, stream->premux_packet->pts)) >= s->packet_size) {
            put_vcd_padding_sector(ctx);
            // FIXME: rounding and first few bytes of each packet
            s->last_scr += s->packet_size * 90000LL / (s->mux_rate * 50LL);
        }
    }

    stream->buffer_index += es_size;
    // FIXME: rounding and first few bytes of each packet
    s->last_scr          += s->packet_size * 90000LL / (s->mux_rate * 50LL);

    while (stream->premux_packet &&
           stream->premux_packet->unwritten_size <= es_size) {
        es_size              -= stream->premux_packet->unwritten_size;
        stream->premux_packet = stream->premux_packet->next;
    }
    if (stream->premux_packet && es_size)
        stream->premux_packet->unwritten_size -= es_size;

    if (remove_decoded_packets(ctx, s->last_scr) < 0)
        return -1;

    return 1;
}

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->codec->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 (pts != AV_NOPTS_VALUE)
        pts += 2 * preload;
    if (dts != AV_NOPTS_VALUE) {
        if (!s->last_scr)
            s->last_scr = dts + preload;
        dts += 2 * preload;
    }

    av_dlog(ctx, "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));
    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;
    }
}

static int mpeg_mux_end(AVFormatContext *ctx)
{
    StreamInfo *stream;
    int i;

    for (;;) {
        int ret = output_packet(ctx, 1);
        if (ret < 0)
            return ret;
        else if (ret == 0)
            break;
    }

    /* End header according to MPEG1 systems standard. We do not write
     * it as it is usually not needed by decoders and because it
     * complicates MPEG stream concatenation. */
    // avio_wb32(ctx->pb, ISO_11172_END_CODE);
    // avio_flush(ctx->pb);

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

        assert(av_fifo_size(stream->fifo) == 0);
        av_fifo_free(stream->fifo);
    }
    return 0;
}

#define OFFSET(x) offsetof(MpegMuxContext, x)
#define E AV_OPT_FLAG_ENCODING_PARAM
static const AVOption options[] = {
    { "muxrate", NULL,                                          OFFSET(mux_rate), AV_OPT_TYPE_INT, { .i64 =      0 }, 0, (1 << 22) - 1, E },
    { "preload", "Initial demux-decode delay in microseconds.", OFFSET(preload),  AV_OPT_TYPE_INT, { .i64 = 500000 }, 0, INT_MAX, E },
    { NULL },
};

#define MPEGENC_CLASS(flavor)                   \
static const AVClass flavor ## _class = {       \
    .class_name = #flavor " muxer",             \
    .item_name  = av_default_item_name,         \
    .version    = LIBAVUTIL_VERSION_INT,        \
    .option     = options,                      \
};

#if CONFIG_MPEG1SYSTEM_MUXER
MPEGENC_CLASS(mpeg)
AVOutputFormat ff_mpeg1system_muxer = {
    .name              = "mpeg",
    .long_name         = NULL_IF_CONFIG_SMALL("MPEG-1 Systems / MPEG program stream"),
    .mime_type         = "video/mpeg",
    .extensions        = "mpg,mpeg",
    .priv_data_size    = sizeof(MpegMuxContext),
    .audio_codec       = AV_CODEC_ID_MP2,
    .video_codec       = AV_CODEC_ID_MPEG1VIDEO,
    .write_header      = mpeg_mux_init,
    .write_packet      = mpeg_mux_write_packet,
    .write_trailer     = mpeg_mux_end,
    .priv_class        = &mpeg_class,
};
#endif

#if CONFIG_MPEG1VCD_MUXER
MPEGENC_CLASS(vcd)
AVOutputFormat ff_mpeg1vcd_muxer = {
    .name              = "vcd",
    .long_name         = NULL_IF_CONFIG_SMALL("MPEG-1 Systems / MPEG program stream (VCD)"),
    .mime_type         = "video/mpeg",
    .priv_data_size    = sizeof(MpegMuxContext),
    .audio_codec       = AV_CODEC_ID_MP2,
    .video_codec       = AV_CODEC_ID_MPEG1VIDEO,
    .write_header      = mpeg_mux_init,
    .write_packet      = mpeg_mux_write_packet,
    .write_trailer     = mpeg_mux_end,
    .priv_class        = &vcd_class,
};
#endif

#if CONFIG_MPEG2VOB_MUXER
MPEGENC_CLASS(vob)
AVOutputFormat ff_mpeg2vob_muxer = {
    .name              = "vob",
    .long_name         = NULL_IF_CONFIG_SMALL("MPEG-2 PS (VOB)"),
    .mime_type         = "video/mpeg",
    .extensions        = "vob",
    .priv_data_size    = sizeof(MpegMuxContext),
    .audio_codec       = AV_CODEC_ID_MP2,
    .video_codec       = AV_CODEC_ID_MPEG2VIDEO,
    .write_header      = mpeg_mux_init,
    .write_packet      = mpeg_mux_write_packet,
    .write_trailer     = mpeg_mux_end,
    .priv_class        = &vob_class,
};
#endif

/* Same as mpeg2vob_mux except that the pack size is 2324 */
#if CONFIG_MPEG2SVCD_MUXER
MPEGENC_CLASS(svcd)
AVOutputFormat ff_mpeg2svcd_muxer = {
    .name              = "svcd",
    .long_name         = NULL_IF_CONFIG_SMALL("MPEG-2 PS (SVCD)"),
    .mime_type         = "video/mpeg",
    .extensions        = "vob",
    .priv_data_size    = sizeof(MpegMuxContext),
    .audio_codec       = AV_CODEC_ID_MP2,
    .video_codec       = AV_CODEC_ID_MPEG2VIDEO,
    .write_header      = mpeg_mux_init,
    .write_packet      = mpeg_mux_write_packet,
    .write_trailer     = mpeg_mux_end,
    .priv_class        = &svcd_class,
};
#endif

/*  Same as mpeg2vob_mux except the 'is_dvd' flag is set to produce NAV pkts */
#if CONFIG_MPEG2DVD_MUXER
MPEGENC_CLASS(dvd)
AVOutputFormat ff_mpeg2dvd_muxer = {
    .name              = "dvd",
    .long_name         = NULL_IF_CONFIG_SMALL("MPEG-2 PS (DVD VOB)"),
    .mime_type         = "video/mpeg",
    .extensions        = "dvd",
    .priv_data_size    = sizeof(MpegMuxContext),
    .audio_codec       = AV_CODEC_ID_MP2,
    .video_codec       = AV_CODEC_ID_MPEG2VIDEO,
    .write_header      = mpeg_mux_init,
    .write_packet      = mpeg_mux_write_packet,
    .write_trailer     = mpeg_mux_end,
    .priv_class        = &dvd_class,
};
#endif