PeerStreamer

/*

 * Matroska muxer

 * Copyright (c) 2007 David Conrad

 *

 * This file is part of FFmpeg.

 *

 * FFmpeg 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.

 *

 * FFmpeg 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 FFmpeg; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

 */

#include "avformat.h"

#include "riff.h"

#include "isom.h"

#include "matroska.h"

#include "avc.h"

#include "flacenc.h"

#include "libavutil/intreadwrite.h"

#include "libavutil/md5.h"

#include "libavcodec/xiph.h"

#include "libavcodec/mpeg4audio.h"

typedef struct ebml_master {

    int64_t         pos;                ///< absolute offset in the file where the master's elements start

    int             sizebytes;          ///< how many bytes were reserved for the size

} ebml_master;

typedef struct mkv_seekhead_entry {

    unsigned int    elementid;

    uint64_t        segmentpos;

} mkv_seekhead_entry;

typedef struct mkv_seekhead {

    int64_t                 filepos;

    int64_t                 segment_offset;     ///< the file offset to the beginning of the segment

    int                     reserved_size;      ///< -1 if appending to file

    int                     max_entries;

    mkv_seekhead_entry      *entries;

    int                     num_entries;

} mkv_seekhead;

typedef struct {

    uint64_t        pts;

    int             tracknum;

    int64_t         cluster_pos;        ///< file offset of the cluster containing the block

} mkv_cuepoint;

typedef struct {

    int64_t         segment_offset;

    mkv_cuepoint    *entries;

    int             num_entries;

} mkv_cues;

typedef struct MatroskaMuxContext {

    ebml_master     segment;

    int64_t         segment_offset;

    int64_t         segment_uid;

    ebml_master     cluster;

    int64_t         cluster_pos;        ///< file offset of the current cluster

    uint64_t        cluster_pts;

    int64_t         duration_offset;

    uint64_t        duration;

    mkv_seekhead    *main_seekhead;

    mkv_seekhead    *cluster_seekhead;

    mkv_cues        *cues;

    struct AVMD5    *md5_ctx;

} MatroskaMuxContext;

/** 2 bytes * 3 for EBML IDs, 3 1-byte EBML lengths, 8 bytes for 64 bit

 * offset, 4 bytes for target EBML ID */

#define MAX_SEEKENTRY_SIZE 21

/** per-cuepoint-track - 3 1-byte EBML IDs, 3 1-byte EBML sizes, 2

 * 8-byte uint max */

#define MAX_CUETRACKPOS_SIZE 22

/** per-cuepoint - 2 1-byte EBML IDs, 2 1-byte EBML sizes, 8-byte uint max */

#define MAX_CUEPOINT_SIZE(num_tracks) 12 + MAX_CUETRACKPOS_SIZE*num_tracks

static int ebml_id_size(unsigned int id)

{

    return (av_log2(id+1)-1)/7+1;

}

static void put_ebml_id(ByteIOContext *pb, unsigned int id)

{

    int i = ebml_id_size(id);

    while (i--)

        put_byte(pb, id >> (i*8));

}

/**

 * Write an EBML size meaning "unknown size".

 *

 * @param bytes The number of bytes the size should occupy (maximum: 8).

 */

static void put_ebml_size_unknown(ByteIOContext *pb, int bytes)

{

    assert(bytes <= 8);

    put_byte(pb, 0x1ff >> bytes);

    while (--bytes)

        put_byte(pb, 0xff);

}

/**

 * Calculate how many bytes are needed to represent a given number in EBML.

 */

static int ebml_num_size(uint64_t num)

{

    int bytes = 1;

    while ((num+1) >> bytes*7) bytes++;

    return bytes;

}

/**

 * Write a number in EBML variable length format.

 *

 * @param bytes The number of bytes that need to be used to write the number.

 *              If zero, any number of bytes can be used.

 */

static void put_ebml_num(ByteIOContext *pb, uint64_t num, int bytes)

{

    int i, needed_bytes = ebml_num_size(num);

    // sizes larger than this are currently undefined in EBML

    assert(num < (1ULL<<56)-1);

    if (bytes == 0)

        // don't care how many bytes are used, so use the min

        bytes = needed_bytes;

    // the bytes needed to write the given size would exceed the bytes

    // that we need to use, so write unknown size. This shouldn't happen.

    assert(bytes >= needed_bytes);

    num |= 1ULL << bytes*7;

    for (i = bytes - 1; i >= 0; i--)

        put_byte(pb, num >> i*8);

}

static void put_ebml_uint(ByteIOContext *pb, unsigned int elementid, uint64_t val)

{

    int i, bytes = 1;

    uint64_t tmp = val;

    while (tmp>>=8) bytes++;

    put_ebml_id(pb, elementid);

    put_ebml_num(pb, bytes, 0);

    for (i = bytes - 1; i >= 0; i--)

        put_byte(pb, val >> i*8);

}

static void put_ebml_float(ByteIOContext *pb, unsigned int elementid, double val)

{

    put_ebml_id(pb, elementid);

    put_ebml_num(pb, 8, 0);

    put_be64(pb, av_dbl2int(val));

}

static void put_ebml_binary(ByteIOContext *pb, unsigned int elementid,

                            const uint8_t *buf, int size)

{

    put_ebml_id(pb, elementid);

    put_ebml_num(pb, size, 0);

    put_buffer(pb, buf, size);

}

static void put_ebml_string(ByteIOContext *pb, unsigned int elementid, const char *str)

{

    put_ebml_binary(pb, elementid, str, strlen(str));

}

/**

 * Writes a void element of a given size. Useful for reserving space in

 * the file to be written to later.

 *

 * @param size The number of bytes to reserve, which must be at least 2.

 */

static void put_ebml_void(ByteIOContext *pb, uint64_t size)

{

    int64_t currentpos = url_ftell(pb);

    assert(size >= 2);

    put_ebml_id(pb, EBML_ID_VOID);

    // we need to subtract the length needed to store the size from the

    // size we need to reserve so 2 cases, we use 8 bytes to store the

    // size if possible, 1 byte otherwise

    if (size < 10)

        put_ebml_num(pb, size-1, 0);

    else

        put_ebml_num(pb, size-9, 8);

    while(url_ftell(pb) < currentpos + size)

        put_byte(pb, 0);

}

static ebml_master start_ebml_master(ByteIOContext *pb, unsigned int elementid, uint64_t expectedsize)

{

    int bytes = expectedsize ? ebml_num_size(expectedsize) : 8;

    put_ebml_id(pb, elementid);

    put_ebml_size_unknown(pb, bytes);

    return (ebml_master){ url_ftell(pb), bytes };

}

static void end_ebml_master(ByteIOContext *pb, ebml_master master)

{

    int64_t pos = url_ftell(pb);

    // leave the unknown size for masters when streaming

    if (url_is_streamed(pb))

        return;

    url_fseek(pb, master.pos - master.sizebytes, SEEK_SET);

    put_ebml_num(pb, pos - master.pos, master.sizebytes);

    url_fseek(pb, pos, SEEK_SET);

}

static void put_xiph_size(ByteIOContext *pb, int size)

{

    int i;

    for (i = 0; i < size / 255; i++)

        put_byte(pb, 255);

    put_byte(pb, size % 255);

}

/**

 * Initialize a mkv_seekhead element to be ready to index level 1 Matroska

 * elements. If a maximum number of elements is specified, enough space

 * will be reserved at the current file location to write a seek head of

 * that size.

 *

 * @param segment_offset The absolute offset to the position in the file

 *                       where the segment begins.

 * @param numelements The maximum number of elements that will be indexed

 *                    by this seek head, 0 if unlimited.

 */

static mkv_seekhead * mkv_start_seekhead(ByteIOContext *pb, int64_t segment_offset, int numelements)

{

    mkv_seekhead *new_seekhead = av_mallocz(sizeof(mkv_seekhead));

    if (new_seekhead == NULL)

        return NULL;

    new_seekhead->segment_offset = segment_offset;

    if (numelements > 0) {

        new_seekhead->filepos = url_ftell(pb);

        // 21 bytes max for a seek entry, 10 bytes max for the SeekHead ID

        // and size, and 3 bytes to guarantee that an EBML void element

        // will fit afterwards

        new_seekhead->reserved_size = numelements * MAX_SEEKENTRY_SIZE + 13;

        new_seekhead->max_entries = numelements;

        put_ebml_void(pb, new_seekhead->reserved_size);

    }

    return new_seekhead;

}

static int mkv_add_seekhead_entry(mkv_seekhead *seekhead, unsigned int elementid, uint64_t filepos)

{

    mkv_seekhead_entry *entries = seekhead->entries;

    // don't store more elements than we reserved space for

    if (seekhead->max_entries > 0 && seekhead->max_entries <= seekhead->num_entries)

        return -1;

    entries = av_realloc(entries, (seekhead->num_entries + 1) * sizeof(mkv_seekhead_entry));

    if (entries == NULL)

        return AVERROR(ENOMEM);

    entries[seekhead->num_entries  ].elementid = elementid;

    entries[seekhead->num_entries++].segmentpos = filepos - seekhead->segment_offset;

    seekhead->entries = entries;

    return 0;

}

/**

 * Write the seek head to the file and free it. If a maximum number of

 * elements was specified to mkv_start_seekhead(), the seek head will

 * be written at the location reserved for it. Otherwise, it is written

 * at the current location in the file.

 *

 * @return The file offset where the seekhead was written.

 */

static int64_t mkv_write_seekhead(ByteIOContext *pb, mkv_seekhead *seekhead)

{

    ebml_master metaseek, seekentry;

    int64_t currentpos;

    int i;

    currentpos = url_ftell(pb);

    if (seekhead->reserved_size > 0)

        url_fseek(pb, seekhead->filepos, SEEK_SET);

    metaseek = start_ebml_master(pb, MATROSKA_ID_SEEKHEAD, seekhead->reserved_size);

    for (i = 0; i < seekhead->num_entries; i++) {

        mkv_seekhead_entry *entry = &seekhead->entries[i];

        seekentry = start_ebml_master(pb, MATROSKA_ID_SEEKENTRY, MAX_SEEKENTRY_SIZE);

        put_ebml_id(pb, MATROSKA_ID_SEEKID);

        put_ebml_num(pb, ebml_id_size(entry->elementid), 0);

        put_ebml_id(pb, entry->elementid);

        put_ebml_uint(pb, MATROSKA_ID_SEEKPOSITION, entry->segmentpos);

        end_ebml_master(pb, seekentry);

    }

    end_ebml_master(pb, metaseek);

    if (seekhead->reserved_size > 0) {

        uint64_t remaining = seekhead->filepos + seekhead->reserved_size - url_ftell(pb);

        put_ebml_void(pb, remaining);

        url_fseek(pb, currentpos, SEEK_SET);

        currentpos = seekhead->filepos;

    }

    av_free(seekhead->entries);

    av_free(seekhead);

    return currentpos;

}

static mkv_cues * mkv_start_cues(int64_t segment_offset)

{

    mkv_cues *cues = av_mallocz(sizeof(mkv_cues));

    if (cues == NULL)

        return NULL;

    cues->segment_offset = segment_offset;

    return cues;

}

static int mkv_add_cuepoint(mkv_cues *cues, AVPacket *pkt, int64_t cluster_pos)

{

    mkv_cuepoint *entries = cues->entries;

    entries = av_realloc(entries, (cues->num_entries + 1) * sizeof(mkv_cuepoint));

    if (entries == NULL)

        return AVERROR(ENOMEM);

    entries[cues->num_entries  ].pts = pkt->pts;

    entries[cues->num_entries  ].tracknum = pkt->stream_index + 1;

    entries[cues->num_entries++].cluster_pos = cluster_pos - cues->segment_offset;

    cues->entries = entries;

    return 0;

}

static int64_t mkv_write_cues(ByteIOContext *pb, mkv_cues *cues, int num_tracks)

{

    ebml_master cues_element;

    int64_t currentpos;

    int i, j;

    currentpos = url_ftell(pb);

    cues_element = start_ebml_master(pb, MATROSKA_ID_CUES, 0);

    for (i = 0; i < cues->num_entries; i++) {

        ebml_master cuepoint, track_positions;

        mkv_cuepoint *entry = &cues->entries[i];

        uint64_t pts = entry->pts;

        cuepoint = start_ebml_master(pb, MATROSKA_ID_POINTENTRY, MAX_CUEPOINT_SIZE(num_tracks));

        put_ebml_uint(pb, MATROSKA_ID_CUETIME, pts);

        // put all the entries from different tracks that have the exact same

        // timestamp into the same CuePoint

        for (j = 0; j < cues->num_entries - i && entry[j].pts == pts; j++) {

            track_positions = start_ebml_master(pb, MATROSKA_ID_CUETRACKPOSITION, MAX_CUETRACKPOS_SIZE);

            put_ebml_uint(pb, MATROSKA_ID_CUETRACK          , entry[j].tracknum   );

            put_ebml_uint(pb, MATROSKA_ID_CUECLUSTERPOSITION, entry[j].cluster_pos);

            end_ebml_master(pb, track_positions);

        }

        i += j - 1;

        end_ebml_master(pb, cuepoint);

    }

    end_ebml_master(pb, cues_element);

    av_free(cues->entries);

    av_free(cues);

    return currentpos;

}

static int put_xiph_codecpriv(AVFormatContext *s, ByteIOContext *pb, AVCodecContext *codec)

{

    uint8_t *header_start[3];

    int header_len[3];

    int first_header_size;

    int j;

    if (codec->codec_id == CODEC_ID_VORBIS)

        first_header_size = 30;

    else

        first_header_size = 42;

    if (ff_split_xiph_headers(codec->extradata, codec->extradata_size,

                              first_header_size, header_start, header_len) < 0) {

        av_log(s, AV_LOG_ERROR, "Extradata corrupt.\n");

        return -1;

    }

    put_byte(pb, 2);                    // number packets - 1

    for (j = 0; j < 2; j++) {

        put_xiph_size(pb, header_len[j]);

    }

    for (j = 0; j < 3; j++)

        put_buffer(pb, header_start[j], header_len[j]);

    return 0;

}

static void get_aac_sample_rates(AVFormatContext *s, AVCodecContext *codec, int *sample_rate, int *output_sample_rate)

{

    int sri;

    if (codec->extradata_size < 2) {

        av_log(s, AV_LOG_WARNING, "No AAC extradata, unable to determine samplerate.\n");

        return;

    }

    sri = ((codec->extradata[0] << 1) & 0xE) | (codec->extradata[1] >> 7);

    if (sri > 12) {

        av_log(s, AV_LOG_WARNING, "AAC samplerate index out of bounds\n");

        return;

    }

    *sample_rate = ff_mpeg4audio_sample_rates[sri];

    // if sbr, get output sample rate as well

    if (codec->extradata_size == 5) {

        sri = (codec->extradata[4] >> 3) & 0xF;

        if (sri > 12) {

            av_log(s, AV_LOG_WARNING, "AAC output samplerate index out of bounds\n");

            return;

        }

        *output_sample_rate = ff_mpeg4audio_sample_rates[sri];

    }

}

static int mkv_write_codecprivate(AVFormatContext *s, ByteIOContext *pb, AVCodecContext *codec, int native_id, int qt_id)

{

    ByteIOContext *dyn_cp;

    uint8_t *codecpriv;

    int ret, codecpriv_size;

    ret = url_open_dyn_buf(&dyn_cp);

    if(ret < 0)

        return ret;

    if (native_id) {

        if (codec->codec_id == CODEC_ID_VORBIS || codec->codec_id == CODEC_ID_THEORA)

            ret = put_xiph_codecpriv(s, dyn_cp, codec);

        else if (codec->codec_id == CODEC_ID_FLAC)

            ret = ff_flac_write_header(dyn_cp, codec);

        else if (codec->codec_id == CODEC_ID_H264)

            ret = ff_isom_write_avcc(dyn_cp, codec->extradata, codec->extradata_size);

        else if (codec->extradata_size)

            put_buffer(dyn_cp, codec->extradata, codec->extradata_size);

    } else if (codec->codec_type == CODEC_TYPE_VIDEO) {

        if (qt_id) {

            if (!codec->codec_tag)

                codec->codec_tag = ff_codec_get_tag(codec_movvideo_tags, codec->codec_id);

            if (codec->extradata_size)

                put_buffer(dyn_cp, codec->extradata, codec->extradata_size);

        } else {

        if (!codec->codec_tag)

            codec->codec_tag = ff_codec_get_tag(ff_codec_bmp_tags, codec->codec_id);

        if (!codec->codec_tag) {

            av_log(s, AV_LOG_ERROR, "No bmp codec ID found.");

            ret = -1;

        }

        ff_put_bmp_header(dyn_cp, codec, ff_codec_bmp_tags, 0);

        }

    } else if (codec->codec_type == CODEC_TYPE_AUDIO) {

        if (!codec->codec_tag)

            codec->codec_tag = ff_codec_get_tag(ff_codec_wav_tags, codec->codec_id);

        if (!codec->codec_tag) {

            av_log(s, AV_LOG_ERROR, "No wav codec ID found.");

            ret = -1;

        }

        ff_put_wav_header(dyn_cp, codec);

    }

    codecpriv_size = url_close_dyn_buf(dyn_cp, &codecpriv);

    if (codecpriv_size)

        put_ebml_binary(pb, MATROSKA_ID_CODECPRIVATE, codecpriv, codecpriv_size);

    av_free(codecpriv);

    return ret;

}

static int mkv_write_tracks(AVFormatContext *s)

{

    MatroskaMuxContext *mkv = s->priv_data;

    ByteIOContext *pb = s->pb;

    ebml_master tracks;

    int i, j, ret;

    ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_TRACKS, url_ftell(pb));

    if (ret < 0) return ret;

    tracks = start_ebml_master(pb, MATROSKA_ID_TRACKS, 0);

    for (i = 0; i < s->nb_streams; i++) {

        AVStream *st = s->streams[i];

        AVCodecContext *codec = st->codec;

        ebml_master subinfo, track;

        int native_id = 0;

        int qt_id = 0;

        int bit_depth = av_get_bits_per_sample(codec->codec_id);

        int sample_rate = codec->sample_rate;

        int output_sample_rate = 0;

        AVMetadataTag *tag;

        if (!bit_depth)

            bit_depth = av_get_bits_per_sample_format(codec->sample_fmt);

        if (codec->codec_id == CODEC_ID_AAC)

            get_aac_sample_rates(s, codec, &sample_rate, &output_sample_rate);

        track = start_ebml_master(pb, MATROSKA_ID_TRACKENTRY, 0);

        put_ebml_uint (pb, MATROSKA_ID_TRACKNUMBER     , i + 1);

        put_ebml_uint (pb, MATROSKA_ID_TRACKUID        , i + 1);

        put_ebml_uint (pb, MATROSKA_ID_TRACKFLAGLACING , 0);    // no lacing (yet)

        put_ebml_float(pb, MATROSKA_ID_TRACKTIMECODESCALE, 1.0);

        if ((tag = av_metadata_get(st->metadata, "title", NULL, 0)))

            put_ebml_string(pb, MATROSKA_ID_TRACKNAME, tag->value);

        tag = av_metadata_get(st->metadata, "language", NULL, 0);

        put_ebml_string(pb, MATROSKA_ID_TRACKLANGUAGE, tag ? tag->value:"und");

        if (st->disposition)

            put_ebml_uint(pb, MATROSKA_ID_TRACKFLAGDEFAULT, !!(st->disposition & AV_DISPOSITION_DEFAULT));

        // look for a codec ID string specific to mkv to use,

        // if none are found, use AVI codes

        for (j = 0; ff_mkv_codec_tags[j].id != CODEC_ID_NONE; j++) {

            if (ff_mkv_codec_tags[j].id == codec->codec_id) {

                put_ebml_string(pb, MATROSKA_ID_CODECID, ff_mkv_codec_tags[j].str);

                native_id = 1;

                break;

            }

        }

        switch (codec->codec_type) {

            case CODEC_TYPE_VIDEO:

                put_ebml_uint(pb, MATROSKA_ID_TRACKTYPE, MATROSKA_TRACK_TYPE_VIDEO);

                if (!native_id &&

                      ff_codec_get_tag(codec_movvideo_tags, codec->codec_id) &&

                    (!ff_codec_get_tag(ff_codec_bmp_tags,   codec->codec_id)

                     || codec->codec_id == CODEC_ID_SVQ1

                     || codec->codec_id == CODEC_ID_SVQ3

                     || codec->codec_id == CODEC_ID_CINEPAK))

                    qt_id = 1;

                if (qt_id)

                    put_ebml_string(pb, MATROSKA_ID_CODECID, "V_QUICKTIME");

                else if (!native_id)

                    // if there is no mkv-specific codec ID, use VFW mode

                    put_ebml_string(pb, MATROSKA_ID_CODECID, "V_MS/VFW/FOURCC");

                subinfo = start_ebml_master(pb, MATROSKA_ID_TRACKVIDEO, 0);

                // XXX: interlace flag?

                put_ebml_uint (pb, MATROSKA_ID_VIDEOPIXELWIDTH , codec->width);

                put_ebml_uint (pb, MATROSKA_ID_VIDEOPIXELHEIGHT, codec->height);

                if (st->sample_aspect_ratio.num) {

                    int d_width = codec->width*av_q2d(st->sample_aspect_ratio);

                    put_ebml_uint(pb, MATROSKA_ID_VIDEODISPLAYWIDTH , d_width);

                    put_ebml_uint(pb, MATROSKA_ID_VIDEODISPLAYHEIGHT, codec->height);

                }

                end_ebml_master(pb, subinfo);

                break;

            case CODEC_TYPE_AUDIO:

                put_ebml_uint(pb, MATROSKA_ID_TRACKTYPE, MATROSKA_TRACK_TYPE_AUDIO);

                if (!native_id)

                    // no mkv-specific ID, use ACM mode

                    put_ebml_string(pb, MATROSKA_ID_CODECID, "A_MS/ACM");

                subinfo = start_ebml_master(pb, MATROSKA_ID_TRACKAUDIO, 0);

                put_ebml_uint  (pb, MATROSKA_ID_AUDIOCHANNELS    , codec->channels);

                put_ebml_float (pb, MATROSKA_ID_AUDIOSAMPLINGFREQ, sample_rate);

                if (output_sample_rate)

                    put_ebml_float(pb, MATROSKA_ID_AUDIOOUTSAMPLINGFREQ, output_sample_rate);

                if (bit_depth)

                    put_ebml_uint(pb, MATROSKA_ID_AUDIOBITDEPTH, bit_depth);

                end_ebml_master(pb, subinfo);

                break;

            case CODEC_TYPE_SUBTITLE:

                put_ebml_uint(pb, MATROSKA_ID_TRACKTYPE, MATROSKA_TRACK_TYPE_SUBTITLE);

                break;

            default:

                av_log(s, AV_LOG_ERROR, "Only audio, video, and subtitles are supported for Matroska.");

                break;

        }

        ret = mkv_write_codecprivate(s, pb, codec, native_id, qt_id);

        if (ret < 0) return ret;

        end_ebml_master(pb, track);

        // ms precision is the de-facto standard timescale for mkv files

        av_set_pts_info(st, 64, 1, 1000);

    }

    end_ebml_master(pb, tracks);

    return 0;

}

static int mkv_write_chapters(AVFormatContext *s)

{

    MatroskaMuxContext *mkv = s->priv_data;

    ByteIOContext *pb = s->pb;

    ebml_master chapters, editionentry;

    AVRational scale = {1, 1E9};

    int i, ret;

    if (!s->nb_chapters)

        return 0;

    ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_CHAPTERS, url_ftell(pb));

    if (ret < 0) return ret;

    chapters     = start_ebml_master(pb, MATROSKA_ID_CHAPTERS    , 0);

    editionentry = start_ebml_master(pb, MATROSKA_ID_EDITIONENTRY, 0);

    put_ebml_uint(pb, MATROSKA_ID_EDITIONFLAGDEFAULT, 1);

    put_ebml_uint(pb, MATROSKA_ID_EDITIONFLAGHIDDEN , 0);

    for (i = 0; i < s->nb_chapters; i++) {

        ebml_master chapteratom, chapterdisplay;

        AVChapter *c     = s->chapters[i];

        AVMetadataTag *t = NULL;

        chapteratom = start_ebml_master(pb, MATROSKA_ID_CHAPTERATOM, 0);

        put_ebml_uint(pb, MATROSKA_ID_CHAPTERUID, c->id);

        put_ebml_uint(pb, MATROSKA_ID_CHAPTERTIMESTART,

                      av_rescale_q(c->start, c->time_base, scale));

        put_ebml_uint(pb, MATROSKA_ID_CHAPTERTIMEEND,

                      av_rescale_q(c->end,   c->time_base, scale));

        put_ebml_uint(pb, MATROSKA_ID_CHAPTERFLAGHIDDEN , 0);

        put_ebml_uint(pb, MATROSKA_ID_CHAPTERFLAGENABLED, 1);

        if ((t = av_metadata_get(c->metadata, "title", NULL, 0))) {

            chapterdisplay = start_ebml_master(pb, MATROSKA_ID_CHAPTERDISPLAY, 0);

            put_ebml_string(pb, MATROSKA_ID_CHAPSTRING, t->value);

            put_ebml_string(pb, MATROSKA_ID_CHAPLANG  , "und");

            end_ebml_master(pb, chapterdisplay);

        }

        end_ebml_master(pb, chapteratom);

    }

    end_ebml_master(pb, editionentry);

    end_ebml_master(pb, chapters);

    return 0;

}

static int mkv_write_header(AVFormatContext *s)

{

    MatroskaMuxContext *mkv = s->priv_data;

    ByteIOContext *pb = s->pb;

    ebml_master ebml_header, segment_info;

    AVMetadataTag *tag;

    int ret;

    mkv->md5_ctx = av_mallocz(av_md5_size);

    av_md5_init(mkv->md5_ctx);

    ebml_header = start_ebml_master(pb, EBML_ID_HEADER, 0);

    put_ebml_uint   (pb, EBML_ID_EBMLVERSION        ,           1);

    put_ebml_uint   (pb, EBML_ID_EBMLREADVERSION    ,           1);

    put_ebml_uint   (pb, EBML_ID_EBMLMAXIDLENGTH    ,           4);

    put_ebml_uint   (pb, EBML_ID_EBMLMAXSIZELENGTH  ,           8);

    put_ebml_string (pb, EBML_ID_DOCTYPE            ,  "matroska");

    put_ebml_uint   (pb, EBML_ID_DOCTYPEVERSION     ,           2);

    put_ebml_uint   (pb, EBML_ID_DOCTYPEREADVERSION ,           2);

    end_ebml_master(pb, ebml_header);

    mkv->segment = start_ebml_master(pb, MATROSKA_ID_SEGMENT, 0);

    mkv->segment_offset = url_ftell(pb);

    // we write 2 seek heads - one at the end of the file to point to each

    // cluster, and one at the beginning to point to all other level one

    // elements (including the seek head at the end of the file), which

    // isn't more than 10 elements if we only write one of each other

    // currently defined level 1 element

    mkv->main_seekhead    = mkv_start_seekhead(pb, mkv->segment_offset, 10);

    mkv->cluster_seekhead = mkv_start_seekhead(pb, mkv->segment_offset, 0);

    if (mkv->main_seekhead == NULL || mkv->cluster_seekhead == NULL)

        return AVERROR(ENOMEM);

    ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_INFO, url_ftell(pb));

    if (ret < 0) return ret;

    segment_info = start_ebml_master(pb, MATROSKA_ID_INFO, 0);

    put_ebml_uint(pb, MATROSKA_ID_TIMECODESCALE, 1000000);

    if ((tag = av_metadata_get(s->metadata, "title", NULL, 0)))

        put_ebml_string(pb, MATROSKA_ID_TITLE, tag->value);

    if (!(s->streams[0]->codec->flags & CODEC_FLAG_BITEXACT)) {

        put_ebml_string(pb, MATROSKA_ID_MUXINGAPP , LIBAVFORMAT_IDENT);

        put_ebml_string(pb, MATROSKA_ID_WRITINGAPP, LIBAVFORMAT_IDENT);

        // reserve space to write the segment UID later

        mkv->segment_uid = url_ftell(pb);

        put_ebml_void(pb, 19);

    }

    // reserve space for the duration

    mkv->duration = 0;

    mkv->duration_offset = url_ftell(pb);

    put_ebml_void(pb, 11);                  // assumes double-precision float to be written

    end_ebml_master(pb, segment_info);

    ret = mkv_write_tracks(s);

    if (ret < 0) return ret;

    ret = mkv_write_chapters(s);

    if (ret < 0) return ret;

    ret = mkv_add_seekhead_entry(mkv->cluster_seekhead, MATROSKA_ID_CLUSTER, url_ftell(pb));

    if (ret < 0) return ret;

    mkv->cluster_pos = url_ftell(pb);

    mkv->cluster = start_ebml_master(pb, MATROSKA_ID_CLUSTER, 0);

    put_ebml_uint(pb, MATROSKA_ID_CLUSTERTIMECODE, 0);

    mkv->cluster_pts = 0;

    mkv->cues = mkv_start_cues(mkv->segment_offset);

    if (mkv->cues == NULL)

        return AVERROR(ENOMEM);

    put_flush_packet(pb);

    return 0;

}

static int mkv_blockgroup_size(int pkt_size)

{

    int size = pkt_size + 4;

    size += ebml_num_size(size);

    size += 2;              // EBML ID for block and block duration

    size += 8;              // max size of block duration

    size += ebml_num_size(size);

    size += 1;              // blockgroup EBML ID

    return size;

}

static int ass_get_duration(const uint8_t *p)

{

    int sh, sm, ss, sc, eh, em, es, ec;

    uint64_t start, end;

    if (sscanf(p, "%*[^,],%d:%d:%d%*c%d,%d:%d:%d%*c%d",

               &sh, &sm, &ss, &sc, &eh, &em, &es, &ec) != 8)

        return 0;

    start = 3600000*sh + 60000*sm + 1000*ss + 10*sc;

    end   = 3600000*eh + 60000*em + 1000*es + 10*ec;

    return end - start;

}

static int mkv_write_ass_blocks(AVFormatContext *s, AVPacket *pkt)

{

    MatroskaMuxContext *mkv = s->priv_data;

    ByteIOContext *pb = s->pb;

    int i, layer = 0, max_duration = 0, size, line_size, data_size = pkt->size;

    uint8_t *start, *end, *data = pkt->data;

    ebml_master blockgroup;

    char buffer[2048];

    while (data_size) {

        int duration = ass_get_duration(data);

        max_duration = FFMAX(duration, max_duration);

        end = memchr(data, '\n', data_size);

        size = line_size = end ? end-data+1 : data_size;

        size -= end ? (end[-1]=='\r')+1 : 0;

        start = data;

        for (i=0; i<3; i++, start++)

            if (!(start = memchr(start, ',', size-(start-data))))

                return max_duration;

        size -= start - data;

        sscanf(data, "Dialogue: %d,", &layer);

        i = snprintf(buffer, sizeof(buffer), "%"PRId64",%d,",

                     s->streams[pkt->stream_index]->nb_frames++, layer);

        size = FFMIN(i+size, sizeof(buffer));

        memcpy(buffer+i, start, size-i);

        av_log(s, AV_LOG_DEBUG, "Writing block at offset %" PRIu64 ", size %d, "

               "pts %" PRId64 ", duration %d\n",

               url_ftell(pb), size, pkt->pts, duration);

        blockgroup = start_ebml_master(pb, MATROSKA_ID_BLOCKGROUP, mkv_blockgroup_size(size));

        put_ebml_id(pb, MATROSKA_ID_BLOCK);

        put_ebml_num(pb, size+4, 0);

        put_byte(pb, 0x80 | (pkt->stream_index + 1));     // this assumes stream_index is less than 126

        put_be16(pb, pkt->pts - mkv->cluster_pts);

        put_byte(pb, 0);

        put_buffer(pb, buffer, size);

        put_ebml_uint(pb, MATROSKA_ID_BLOCKDURATION, duration);

        end_ebml_master(pb, blockgroup);

        data += line_size;

        data_size -= line_size;

    }

    return max_duration;

}

static void mkv_write_block(AVFormatContext *s, unsigned int blockid, AVPacket *pkt, int flags)

{

    MatroskaMuxContext *mkv = s->priv_data;

    ByteIOContext *pb = s->pb;

    AVCodecContext *codec = s->streams[pkt->stream_index]->codec;

    uint8_t *data = NULL;

    int size = pkt->size;

    av_log(s, AV_LOG_DEBUG, "Writing block at offset %" PRIu64 ", size %d, "

           "pts %" PRId64 ", dts %" PRId64 ", duration %d, flags %d\n",

           url_ftell(pb), pkt->size, pkt->pts, pkt->dts, pkt->duration, flags);

    if (codec->codec_id == CODEC_ID_H264 && codec->extradata_size > 0 &&

        (AV_RB24(codec->extradata) == 1 || AV_RB32(codec->extradata) == 1))

        ff_avc_parse_nal_units_buf(pkt->data, &data, &size);

    else

        data = pkt->data;

    put_ebml_id(pb, blockid);

    put_ebml_num(pb, size+4, 0);

    put_byte(pb, 0x80 | (pkt->stream_index + 1));     // this assumes stream_index is less than 126

    put_be16(pb, pkt->pts - mkv->cluster_pts);

    put_byte(pb, flags);

    put_buffer(pb, data, size);

    if (data != pkt->data)

        av_free(data);

}

static int mkv_write_packet(AVFormatContext *s, AVPacket *pkt)

{

    MatroskaMuxContext *mkv = s->priv_data;

    ByteIOContext *pb = s->pb;

    AVCodecContext *codec = s->streams[pkt->stream_index]->codec;

    int keyframe = !!(pkt->flags & PKT_FLAG_KEY);

    int duration = pkt->duration;

    int ret;

    // start a new cluster every 5 MB or 5 sec

    if (url_ftell(pb) > mkv->cluster_pos + 5*1024*1024 || pkt->pts > mkv->cluster_pts + 5000) {

        av_log(s, AV_LOG_DEBUG, "Starting new cluster at offset %" PRIu64

               " bytes, pts %" PRIu64 "\n", url_ftell(pb), pkt->pts);

        end_ebml_master(pb, mkv->cluster);

        ret = mkv_add_seekhead_entry(mkv->cluster_seekhead, MATROSKA_ID_CLUSTER, url_ftell(pb));

        if (ret < 0) return ret;

        mkv->cluster_pos = url_ftell(pb);

        mkv->cluster = start_ebml_master(pb, MATROSKA_ID_CLUSTER, 0);

        put_ebml_uint(pb, MATROSKA_ID_CLUSTERTIMECODE, pkt->pts);

        mkv->cluster_pts = pkt->pts;

        av_md5_update(mkv->md5_ctx, pkt->data, FFMIN(200, pkt->size));

    }

    if (codec->codec_type != CODEC_TYPE_SUBTITLE) {

        mkv_write_block(s, MATROSKA_ID_SIMPLEBLOCK, pkt, keyframe << 7);

    } else if (codec->codec_id == CODEC_ID_SSA) {

        duration = mkv_write_ass_blocks(s, pkt);

    } else {

        ebml_master blockgroup = start_ebml_master(pb, MATROSKA_ID_BLOCKGROUP, mkv_blockgroup_size(pkt->size));

        duration = pkt->convergence_duration;

        mkv_write_block(s, MATROSKA_ID_BLOCK, pkt, 0);

        put_ebml_uint(pb, MATROSKA_ID_BLOCKDURATION, duration);

        end_ebml_master(pb, blockgroup);

    }

    if (codec->codec_type == CODEC_TYPE_VIDEO && keyframe) {

        ret = mkv_add_cuepoint(mkv->cues, pkt, mkv->cluster_pos);

        if (ret < 0) return ret;

    }

    mkv->duration = FFMAX(mkv->duration, pkt->pts + duration);

    return 0;

}

static int mkv_write_trailer(AVFormatContext *s)

{

    MatroskaMuxContext *mkv = s->priv_data;

    ByteIOContext *pb = s->pb;

    int64_t currentpos, second_seekhead, cuespos;

    int ret;

    end_ebml_master(pb, mkv->cluster);

    if (!url_is_streamed(pb)) {

        cuespos = mkv_write_cues(pb, mkv->cues, s->nb_streams);

        second_seekhead = mkv_write_seekhead(pb, mkv->cluster_seekhead);

        ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_CUES    , cuespos);

        if (ret < 0) return ret;

        ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_SEEKHEAD, second_seekhead);

        if (ret < 0) return ret;

        mkv_write_seekhead(pb, mkv->main_seekhead);

        // update the duration

        av_log(s, AV_LOG_DEBUG, "end duration = %" PRIu64 "\n", mkv->duration);

        currentpos = url_ftell(pb);

        url_fseek(pb, mkv->duration_offset, SEEK_SET);

        put_ebml_float(pb, MATROSKA_ID_DURATION, mkv->duration);

        // write the md5sum of some frames as the segment UID

        if (!(s->streams[0]->codec->flags & CODEC_FLAG_BITEXACT)) {

            uint8_t segment_uid[16];

            av_md5_final(mkv->md5_ctx, segment_uid);

            url_fseek(pb, mkv->segment_uid, SEEK_SET);

            put_ebml_binary(pb, MATROSKA_ID_SEGMENTUID, segment_uid, 16);

        }

        url_fseek(pb, currentpos, SEEK_SET);

    }

    end_ebml_master(pb, mkv->segment);

    av_free(mkv->md5_ctx);

    put_flush_packet(pb);

    return 0;

}

AVOutputFormat matroska_muxer = {

    "matroska",

    NULL_IF_CONFIG_SMALL("Matroska file format"),

    "video/x-matroska",

    "mkv",

    sizeof(MatroskaMuxContext),

    CODEC_ID_MP2,

    CODEC_ID_MPEG4,

    mkv_write_header,

    mkv_write_packet,

    mkv_write_trailer,

    .flags = AVFMT_GLOBALHEADER | AVFMT_VARIABLE_FPS,

    .codec_tag = (const AVCodecTag* const []){ff_codec_bmp_tags, ff_codec_wav_tags, 0},

    .subtitle_codec = CODEC_ID_TEXT,

};

AVOutputFormat matroska_audio_muxer = {

    "matroska",

    NULL_IF_CONFIG_SMALL("Matroska file format"),

    "audio/x-matroska",

    "mka",

    sizeof(MatroskaMuxContext),