/*

  * 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 "internal.h"

 #include "riff.h"

 #include "isom.h"

 #include "matroska.h"

 #include "avc.h"

 #include "flacenc.h"

 #include "avlanguage.h"

 #include "libavutil/samplefmt.h"

 #include "libavutil/sha.h"

 #include "libavutil/intreadwrite.h"

 #include "libavutil/intfloat.h"

 #include "libavutil/mathematics.h"

 #include "libavutil/random_seed.h"
 #include "libavutil/lfg.h"

 #include "libavutil/dict.h"

 #include "libavutil/avstring.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 {
     int             write_dts;
 } mkv_track;
 

 #define MODE_MATROSKAv2 0x01
 #define MODE_WEBM       0x02
 

 typedef struct MatroskaMuxContext {

     int             mode;

     AVIOContext   *dyn_bc;

     ebml_master     segment;

     int64_t         segment_offset;

     ebml_master     cluster;

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

     int64_t         cluster_pts;

     int64_t         duration_offset;

     int64_t         duration;

     mkv_seekhead    *main_seekhead;

     mkv_cues        *cues;

     mkv_track       *tracks;

     unsigned int    audio_buffer_size;
     AVPacket        cur_audio_pkt;

 
     int have_attachments;

 
     int64_t ts_offset;

 } 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(AVIOContext *pb, unsigned int id)

 {

     int i = ebml_id_size(id);
     while (i--)

         avio_w8(pb, (uint8_t)(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(AVIOContext *pb, int bytes)

 {

     av_assert0(bytes <= 8);

     avio_w8(pb, 0x1ff >> bytes);

     while (--bytes)

         avio_w8(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(AVIOContext *pb, uint64_t num, int bytes)

 {

     int i, needed_bytes = ebml_num_size(num);

 
     // sizes larger than this are currently undefined in EBML

     av_assert0(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.

     av_assert0(bytes >= needed_bytes);

     num |= 1ULL << bytes*7;

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

         avio_w8(pb, (uint8_t)(num >> i*8));

 }
 

 static void put_ebml_uint(AVIOContext *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--)

         avio_w8(pb, (uint8_t)(val >> i*8));

 }
 

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

 {
     put_ebml_id(pb, elementid);

     put_ebml_num(pb, 8, 0);

     avio_wb64(pb, av_double2int(val));

 }
 

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

                             const void *buf, int size)

 {
     put_ebml_id(pb, elementid);

     put_ebml_num(pb, size, 0);

     avio_write(pb, buf, size);

 }
 

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

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

 /**

  * Write 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(AVIOContext *pb, uint64_t size)

 {

     int64_t currentpos = avio_tell(pb);

     av_assert0(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(avio_tell(pb) < currentpos + size)

         avio_w8(pb, 0);

 }
 

 static ebml_master start_ebml_master(AVIOContext *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){ avio_tell(pb), bytes };

 }
 

 static void end_ebml_master(AVIOContext *pb, ebml_master master)

 {

     int64_t pos = avio_tell(pb);

     if (avio_seek(pb, master.pos - master.sizebytes, SEEK_SET) < 0)

         return;

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

     avio_seek(pb, pos, SEEK_SET);

 }
 

 static void put_xiph_size(AVIOContext *pb, int size)

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

         avio_w8(pb, 255);
     avio_w8(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(AVIOContext *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 = avio_tell(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,
  * -1 if an error occurred.

  */

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

 {

     ebml_master metaseek, seekentry;

     int64_t currentpos;

     int i;
 

     currentpos = avio_tell(pb);

     if (seekhead->reserved_size > 0) {
         if (avio_seek(pb, seekhead->filepos, SEEK_SET) < 0) {
             currentpos = -1;
             goto fail;
         }
     }

     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 - avio_tell(pb);

         put_ebml_void(pb, remaining);

         avio_seek(pb, currentpos, SEEK_SET);

 
         currentpos = seekhead->filepos;
     }

 fail:

     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, int stream, int64_t ts, int64_t cluster_pos)

 {
     mkv_cuepoint *entries = cues->entries;
 

     if (ts < 0)
         return 0;
 

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

         return AVERROR(ENOMEM);

     entries[cues->num_entries  ].pts = ts;
     entries[cues->num_entries  ].tracknum = stream + 1;

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

 
     cues->entries = entries;
     return 0;
 }
 

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

 {

     ebml_master cues_element;

     int64_t currentpos;

     int i, j;
 

     currentpos = avio_tell(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);
 
     return currentpos;
 }
 

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

 {
     uint8_t *header_start[3];
     int header_len[3];
     int first_header_size;

     int j;

     if (codec->codec_id == AV_CODEC_ID_VORBIS)

         first_header_size = 30;
     else
         first_header_size = 42;
 

     if (avpriv_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;
     }
 

     avio_w8(pb, 2);                    // number packets - 1

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

         put_xiph_size(pb, header_len[j]);

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

         avio_write(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)

 {

     MPEG4AudioConfig mp4ac;

     if (avpriv_mpeg4audio_get_config(&mp4ac, codec->extradata,
                                      codec->extradata_size * 8, 1) < 0) {

         av_log(s, AV_LOG_WARNING, "Error parsing AAC extradata, unable to determine samplerate.\n");

         return;
     }
 

     *sample_rate        = mp4ac.sample_rate;
     *output_sample_rate = mp4ac.ext_sample_rate;

 }
 

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

 {

     AVIOContext *dyn_cp;

     uint8_t *codecpriv;

     int ret, codecpriv_size;

     ret = avio_open_dyn_buf(&dyn_cp);

     if(ret < 0)
         return ret;

 
     if (native_id) {

         if (codec->codec_id == AV_CODEC_ID_VORBIS || codec->codec_id == AV_CODEC_ID_THEORA)

             ret = put_xiph_codecpriv(s, dyn_cp, codec);

         else if (codec->codec_id == AV_CODEC_ID_FLAC)

             ret = ff_flac_write_header(dyn_cp, codec, 1);

         else if (codec->codec_id == AV_CODEC_ID_H264)

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

         else if (codec->codec_id == AV_CODEC_ID_ALAC) {
             if (codec->extradata_size < 36) {
                 av_log(s, AV_LOG_ERROR,
                        "Invalid extradata found, ALAC expects a 36-byte "
                        "QuickTime atom.");
                 ret = AVERROR_INVALIDDATA;
             } else
                 avio_write(dyn_cp, codec->extradata + 12,
                                    codec->extradata_size - 12);
         }

         else if (codec->extradata_size)

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

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

         if (qt_id) {
             if (!codec->codec_tag)

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

             if (codec->extradata_size)

                 avio_write(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.\n");

                 ret = -1;
             }

             ff_put_bmp_header(dyn_cp, codec, ff_codec_bmp_tags, 0);

         }

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

         unsigned int tag;
         tag = ff_codec_get_tag(ff_codec_wav_tags, codec->codec_id);
         if (!tag) {

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

             ret = -1;

         }

         if (!codec->codec_tag)
             codec->codec_tag = tag;

         ff_put_wav_header(dyn_cp, codec);

     }

     codecpriv_size = avio_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;

     AVIOContext *pb = s->pb;

     ebml_master tracks;

     int i, j, ret;

     ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_TRACKS, avio_tell(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;

         AVDictionaryEntry *tag;

         if (codec->codec_type == AVMEDIA_TYPE_ATTACHMENT) {
             mkv->have_attachments = 1;
             continue;
         }
 

         if (!bit_depth)

             bit_depth = av_get_bytes_per_sample(codec->sample_fmt) << 3;

         if (codec->codec_id == AV_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)
 

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

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

         tag = av_dict_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 != AV_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;
             }
         }
 

         if (mkv->mode == MODE_WEBM && !(codec->codec_id == AV_CODEC_ID_VP8 ||
                                         codec->codec_id == AV_CODEC_ID_VORBIS)) {

             av_log(s, AV_LOG_ERROR,
                    "Only VP8 video and Vorbis audio are supported for WebM.\n");
             return AVERROR(EINVAL);
         }
 

         switch (codec->codec_type) {

             case AVMEDIA_TYPE_VIDEO:

                 put_ebml_uint(pb, MATROSKA_ID_TRACKTYPE, MATROSKA_TRACK_TYPE_VIDEO);

                 if(st->avg_frame_rate.num && st->avg_frame_rate.den && 1.0/av_q2d(st->avg_frame_rate) > av_q2d(codec->time_base))
                     put_ebml_uint(pb, MATROSKA_ID_TRACKDEFAULTDURATION, 1E9/av_q2d(st->avg_frame_rate));
                 else
                     put_ebml_uint(pb, MATROSKA_ID_TRACKDEFAULTDURATION, av_q2d(codec->time_base)*1E9);

                 if (!native_id &&

                       ff_codec_get_tag(ff_codec_movvideo_tags, codec->codec_id) &&

                     (!ff_codec_get_tag(ff_codec_bmp_tags,   codec->codec_id)

                      || codec->codec_id == AV_CODEC_ID_SVQ1
                      || codec->codec_id == AV_CODEC_ID_SVQ3
                      || codec->codec_id == AV_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");

                     mkv->tracks[i].write_dts = 1;
                 }

                 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 ((tag = av_dict_get(st->metadata, "stereo_mode", NULL, 0)) ||
                     (tag = av_dict_get( s->metadata, "stereo_mode", NULL, 0))) {

                     // save stereo mode flag
                     uint64_t st_mode = MATROSKA_VIDEO_STEREO_MODE_COUNT;
 
                     for (j=0; j<MATROSKA_VIDEO_STEREO_MODE_COUNT; j++)

                         if (!strcmp(tag->value, ff_matroska_video_stereo_mode[j])){

                             st_mode = j;

                             break;

                         }
 
                     if ((mkv->mode == MODE_WEBM && st_mode > 3 && st_mode != 11)
                         || st_mode >= MATROSKA_VIDEO_STEREO_MODE_COUNT) {
                         av_log(s, AV_LOG_ERROR,
                                "The specified stereo mode is not valid.\n");
                         return AVERROR(EINVAL);
                     } else
                         put_ebml_uint(pb, MATROSKA_ID_VIDEOSTEREOMODE, st_mode);

                 }

                 if (st->sample_aspect_ratio.num) {

                     int64_t d_width = av_rescale(codec->width, st->sample_aspect_ratio.num, st->sample_aspect_ratio.den);
                     if (d_width > INT_MAX) {
                         av_log(s, AV_LOG_ERROR, "Overflow in display width\n");
                         return AVERROR(EINVAL);
                     }

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

                 }

                 if (codec->codec_id == AV_CODEC_ID_RAWVIDEO) {

                     uint32_t color_space = av_le2ne32(codec->codec_tag);
                     put_ebml_binary(pb, MATROSKA_ID_VIDEOCOLORSPACE, &color_space, sizeof(color_space));
                 }

                 end_ebml_master(pb, subinfo);
                 break;
 

             case AVMEDIA_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 AVMEDIA_TYPE_SUBTITLE:

                 put_ebml_uint(pb, MATROSKA_ID_TRACKTYPE, MATROSKA_TRACK_TYPE_SUBTITLE);

                 if (!native_id) {
                     av_log(s, AV_LOG_ERROR, "Subtitle codec %d is not supported.\n", codec->codec_id);

                     return AVERROR(ENOSYS);

                 }

                 break;

             default:

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

                 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

         avpriv_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;

     AVIOContext *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, avio_tell(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];

         AVDictionaryEntry *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_dict_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 void mkv_write_simpletag(AVIOContext *pb, AVDictionaryEntry *t)

 {
     uint8_t *key = av_strdup(t->key);
     uint8_t *p   = key;
     const uint8_t *lang = NULL;
     ebml_master tag;
 
     if ((p = strrchr(p, '-')) &&
         (lang = av_convert_lang_to(p + 1, AV_LANG_ISO639_2_BIBL)))
         *p = 0;
 
     p = key;
     while (*p) {
         if (*p == ' ')
             *p = '_';
         else if (*p >= 'a' && *p <= 'z')
             *p -= 'a' - 'A';
         p++;
     }
 
     tag = start_ebml_master(pb, MATROSKA_ID_SIMPLETAG, 0);
     put_ebml_string(pb, MATROSKA_ID_TAGNAME, key);
     if (lang)
         put_ebml_string(pb, MATROSKA_ID_TAGLANG, lang);
     put_ebml_string(pb, MATROSKA_ID_TAGSTRING, t->value);
     end_ebml_master(pb, tag);
 
     av_freep(&key);
 }
 

 static int mkv_write_tag(AVFormatContext *s, AVDictionary *m, unsigned int elementid,

                          unsigned int uid, ebml_master *tags)
 {
     MatroskaMuxContext *mkv = s->priv_data;
     ebml_master tag, targets;

     AVDictionaryEntry *t = NULL;

     int ret;
 
     if (!tags->pos) {

         ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_TAGS, avio_tell(s->pb));

         if (ret < 0) return ret;
 
         *tags = start_ebml_master(s->pb, MATROSKA_ID_TAGS, 0);
     }
 
     tag     = start_ebml_master(s->pb, MATROSKA_ID_TAG,        0);
     targets = start_ebml_master(s->pb, MATROSKA_ID_TAGTARGETS, 0);
     if (elementid)
         put_ebml_uint(s->pb, elementid, uid);
     end_ebml_master(s->pb, targets);
 

     while ((t = av_dict_get(m, "", t, AV_DICT_IGNORE_SUFFIX)))

         if (av_strcasecmp(t->key, "title") &&

             av_strcasecmp(t->key, "stereo_mode") &&

             av_strcasecmp(t->key, "encoding_tool"))

             mkv_write_simpletag(s->pb, t);

 
     end_ebml_master(s->pb, tag);
     return 0;
 }
 

 static int mkv_check_tag(AVDictionary *m)
 {
     AVDictionaryEntry *t = NULL;
 
     while ((t = av_dict_get(m, "", t, AV_DICT_IGNORE_SUFFIX)))
         if (av_strcasecmp(t->key, "title") && av_strcasecmp(t->key, "stereo_mode"))

             return 1;

     return 0;

 }
 

 static int mkv_write_tags(AVFormatContext *s)
 {
     ebml_master tags = {0};
     int i, ret;
 

     ff_metadata_conv_ctx(s, ff_mkv_metadata_conv, NULL);
 

     if (mkv_check_tag(s->metadata)) {

         ret = mkv_write_tag(s, s->metadata, 0, 0, &tags);
         if (ret < 0) return ret;
     }
 
     for (i = 0; i < s->nb_streams; i++) {
         AVStream *st = s->streams[i];
 

         if (!mkv_check_tag(st->metadata))

             continue;
 
         ret = mkv_write_tag(s, st->metadata, MATROSKA_ID_TAGTARGETS_TRACKUID, i + 1, &tags);
         if (ret < 0) return ret;
     }
 
     for (i = 0; i < s->nb_chapters; i++) {
         AVChapter *ch = s->chapters[i];
 

         if (!mkv_check_tag(ch->metadata))

             continue;
 
         ret = mkv_write_tag(s, ch->metadata, MATROSKA_ID_TAGTARGETS_CHAPTERUID, ch->id, &tags);
         if (ret < 0) return ret;
     }
 
     if (tags.pos)
         end_ebml_master(s->pb, tags);
     return 0;
 }
 

 static int mkv_write_attachments(AVFormatContext *s)
 {
     MatroskaMuxContext *mkv = s->priv_data;
     AVIOContext *pb = s->pb;
     ebml_master attachments;
     AVLFG c;
     int i, ret;
 
     if (!mkv->have_attachments)
         return 0;
 
     av_lfg_init(&c, av_get_random_seed());
 
     ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_ATTACHMENTS, avio_tell(pb));
     if (ret < 0) return ret;
 
     attachments = start_ebml_master(pb, MATROSKA_ID_ATTACHMENTS, 0);
 
     for (i = 0; i < s->nb_streams; i++) {
         AVStream *st = s->streams[i];
         ebml_master attached_file;
         AVDictionaryEntry *t;
         const char *mimetype = NULL;

         uint64_t fileuid;

 
         if (st->codec->codec_type != AVMEDIA_TYPE_ATTACHMENT)
             continue;
 
         attached_file = start_ebml_master(pb, MATROSKA_ID_ATTACHEDFILE, 0);
 
         if (t = av_dict_get(st->metadata, "title", NULL, 0))
             put_ebml_string(pb, MATROSKA_ID_FILEDESC, t->value);
         if (!(t = av_dict_get(st->metadata, "filename", NULL, 0))) {
             av_log(s, AV_LOG_ERROR, "Attachment stream %d has no filename tag.\n", i);
             return AVERROR(EINVAL);
         }
         put_ebml_string(pb, MATROSKA_ID_FILENAME, t->value);
         if (t = av_dict_get(st->metadata, "mimetype", NULL, 0))
             mimetype = t->value;

         else if (st->codec->codec_id != AV_CODEC_ID_NONE ) {

             int i;

             for (i = 0; ff_mkv_mime_tags[i].id != AV_CODEC_ID_NONE; i++)

                 if (ff_mkv_mime_tags[i].id == st->codec->codec_id) {
                     mimetype = ff_mkv_mime_tags[i].str;
                     break;
                 }
         }
         if (!mimetype) {
             av_log(s, AV_LOG_ERROR, "Attachment stream %d has no mimetype tag and "
                                     "it cannot be deduced from the codec id.\n", i);
             return AVERROR(EINVAL);
         }
 

         if (st->codec->flags & CODEC_FLAG_BITEXACT) {
             struct AVSHA *sha = av_sha_alloc();
             uint8_t digest[20];
             if (!sha)
                 return AVERROR(ENOMEM);
             av_sha_init(sha, 160);
             av_sha_update(sha, st->codec->extradata, st->codec->extradata_size);
             av_sha_final(sha, digest);
             av_free(sha);
             fileuid = AV_RL64(digest);
         } else {
             fileuid = av_lfg_get(&c);
         }
         av_log(s, AV_LOG_VERBOSE, "Using %.16"PRIx64" for attachment %d\n",
                fileuid, i);
 

         put_ebml_string(pb, MATROSKA_ID_FILEMIMETYPE, mimetype);
         put_ebml_binary(pb, MATROSKA_ID_FILEDATA, st->codec->extradata, st->codec->extradata_size);

         put_ebml_uint(pb, MATROSKA_ID_FILEUID, fileuid);

         end_ebml_master(pb, attached_file);
     }
     end_ebml_master(pb, attachments);
 
     return 0;
 }
 

 static int mkv_write_header(AVFormatContext *s)
 {
     MatroskaMuxContext *mkv = s->priv_data;

     AVIOContext *pb = s->pb;

     ebml_master ebml_header, segment_info;

     AVDictionaryEntry *tag;

     int ret, i;

     if (!strcmp(s->oformat->name, "webm")) mkv->mode = MODE_WEBM;
     else                                   mkv->mode = MODE_MATROSKAv2;
 

     if (s->avoid_negative_ts < 0)
         s->avoid_negative_ts = 1;
 

     mkv->tracks = av_mallocz(s->nb_streams * sizeof(*mkv->tracks));

     if (!mkv->tracks)
         return AVERROR(ENOMEM);

     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            , s->oformat->name);

     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 = avio_tell(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);

     if (!mkv->main_seekhead)

         return AVERROR(ENOMEM);

     ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_INFO, avio_tell(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_dict_get(s->metadata, "title", NULL, 0)))

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

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

         uint32_t segment_uid[4];

         AVLFG lfg;
 
         av_lfg_init(&lfg, av_get_random_seed());
 

         for (i = 0; i < 4; i++)

             segment_uid[i] = av_lfg_get(&lfg);

         put_ebml_string(pb, MATROSKA_ID_MUXINGAPP , LIBAVFORMAT_IDENT);

         if ((tag = av_dict_get(s->metadata, "encoding_tool", NULL, 0)))
             put_ebml_string(pb, MATROSKA_ID_WRITINGAPP, tag->value);
         else
             put_ebml_string(pb, MATROSKA_ID_WRITINGAPP, LIBAVFORMAT_IDENT);

         put_ebml_binary(pb, MATROSKA_ID_SEGMENTUID, segment_uid, 16);

     }

     if (tag = av_dict_get(s->metadata, "creation_time", NULL, 0)) {
         // Adjust time so it's relative to 2001-01-01 and convert to nanoseconds.
         int64_t date_utc = (ff_iso8601_to_unix_time(tag->value) - 978307200) * 1000000000;
         uint8_t date_utc_buf[8];
         AV_WB64(date_utc_buf, date_utc);
         put_ebml_binary(pb, MATROSKA_ID_DATEUTC, date_utc_buf, 8);
     }
 

     // reserve space for the duration
     mkv->duration = 0;

     mkv->duration_offset = avio_tell(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;

     if (mkv->mode != MODE_WEBM) {
         ret = mkv_write_chapters(s);
         if (ret < 0) return ret;

 
         ret = mkv_write_tags(s);
         if (ret < 0) return ret;

 
         ret = mkv_write_attachments(s);
         if (ret < 0) return ret;

     }

     if (!s->pb->seekable)

         mkv_write_seekhead(pb, mkv->main_seekhead);
 

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

         return AVERROR(ENOMEM);

     av_init_packet(&mkv->cur_audio_pkt);
     mkv->cur_audio_pkt.size = 0;
     mkv->audio_buffer_size  = 0;

     mkv->cluster_pos = -1;

     avio_flush(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 = 3600000LL*sh + 60000LL*sm + 1000LL*ss + 10LL*sc;
     end   = 3600000LL*eh + 60000LL*em + 1000LL*es + 10LL*ec;

     return end - start;
 }
 

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

 {
     MatroskaMuxContext *mkv = s->priv_data;
     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",

                avio_tell(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);

         avio_w8(pb, 0x80 | (pkt->stream_index + 1));     // this assumes stream_index is less than 126
         avio_wb16(pb, pkt->pts - mkv->cluster_pts);
         avio_w8(pb, 0);
         avio_write(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, AVIOContext *pb,

                             unsigned int blockid, AVPacket *pkt, int flags)

 {
     MatroskaMuxContext *mkv = s->priv_data;

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

     uint8_t *data = NULL;

     int offset = 0, size = pkt->size;

     int64_t ts = mkv->tracks[pkt->stream_index].write_dts ? pkt->dts : pkt->pts;

     av_log(s, AV_LOG_DEBUG, "Writing block at offset %" PRIu64 ", size %d, "
            "pts %" PRId64 ", dts %" PRId64 ", duration %d, flags %d\n",

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

     if (codec->codec_id == AV_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;

 
     if (codec->codec_id == AV_CODEC_ID_PRORES) {
         /* Matroska specification requires to remove the first QuickTime atom
          */
         size -= 8;
         offset = 8;
     }
 

     put_ebml_id(pb, blockid);

     put_ebml_num(pb, size+4, 0);

     avio_w8(pb, 0x80 | (pkt->stream_index + 1));     // this assumes stream_index is less than 126
     avio_wb16(pb, ts - mkv->cluster_pts);
     avio_w8(pb, flags);

     avio_write(pb, data + offset, size);

     if (data != pkt->data)
         av_free(data);

 }
 

 static int srt_get_duration(uint8_t **buf)
 {
     int i, duration = 0;
 
     for (i=0; i<2 && !duration; i++) {
         int s_hour, s_min, s_sec, s_hsec, e_hour, e_min, e_sec, e_hsec;
         if (sscanf(*buf, "%d:%2d:%2d%*1[,.]%3d --> %d:%2d:%2d%*1[,.]%3d",
                    &s_hour, &s_min, &s_sec, &s_hsec,
                    &e_hour, &e_min, &e_sec, &e_hsec) == 8) {
             s_min  +=   60*s_hour;      e_min  +=   60*e_hour;
             s_sec  +=   60*s_min;       e_sec  +=   60*e_min;
             s_hsec += 1000*s_sec;       e_hsec += 1000*e_sec;
             duration = e_hsec - s_hsec;
         }
         *buf += strcspn(*buf, "\n") + 1;
     }
     return duration;
 }
 

 static int mkv_write_srt_blocks(AVFormatContext *s, AVIOContext *pb, AVPacket *pkt)

 {
     ebml_master blockgroup;
     AVPacket pkt2 = *pkt;
     int64_t duration = srt_get_duration(&pkt2.data);
     pkt2.size -= pkt2.data - pkt->data;
 
     blockgroup = start_ebml_master(pb, MATROSKA_ID_BLOCKGROUP,
                                    mkv_blockgroup_size(pkt2.size));
     mkv_write_block(s, pb, MATROSKA_ID_BLOCK, &pkt2, 0);
     put_ebml_uint(pb, MATROSKA_ID_BLOCKDURATION, duration);
     end_ebml_master(pb, blockgroup);
 
     return duration;
 }
 

 static void mkv_flush_dynbuf(AVFormatContext *s)
 {
     MatroskaMuxContext *mkv = s->priv_data;
     int bufsize;
     uint8_t *dyn_buf;
 
     if (!mkv->dyn_bc)
         return;
 

     bufsize = avio_close_dyn_buf(mkv->dyn_bc, &dyn_buf);

     avio_write(s->pb, dyn_buf, bufsize);

     av_free(dyn_buf);
     mkv->dyn_bc = NULL;
 }
 

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

 {

     MatroskaMuxContext *mkv = s->priv_data;

     AVIOContext *pb = s->pb;

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

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

     int duration = pkt->duration;

     int ret;

     int64_t ts = mkv->tracks[pkt->stream_index].write_dts ? pkt->dts : pkt->pts;

     if (ts == AV_NOPTS_VALUE) {
         av_log(s, AV_LOG_ERROR, "Can't write packet with unknown timestamp\n");
         return AVERROR(EINVAL);
     }
 

     if (!s->pb->seekable) {

         if (!mkv->dyn_bc) {
             if ((ret = avio_open_dyn_buf(&mkv->dyn_bc)) < 0) {
                 av_log(s, AV_LOG_ERROR, "Failed to open dynamic buffer\n");
                 return ret;
             }
         }

         pb = mkv->dyn_bc;
     }
 

     if (mkv->cluster_pos == -1) {

         mkv->cluster_pos = avio_tell(s->pb);

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

         put_ebml_uint(pb, MATROSKA_ID_CLUSTERTIMECODE, FFMAX(0, ts));
         mkv->cluster_pts = FFMAX(0, ts);

     }
 

     if (codec->codec_type != AVMEDIA_TYPE_SUBTITLE) {

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

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

         duration = mkv_write_ass_blocks(s, pb, pkt);

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

         duration = mkv_write_srt_blocks(s, pb, pkt);

     } else {

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

         /* For backward compatibility, prefer convergence_duration. */
         if (pkt->convergence_duration > 0) {
             duration = pkt->convergence_duration;
         }

         mkv_write_block(s, pb, MATROSKA_ID_BLOCK, pkt, 0);

         put_ebml_uint(pb, MATROSKA_ID_BLOCKDURATION, duration);

         end_ebml_master(pb, blockgroup);
     }

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

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

         if (ret < 0) return ret;

     }
 

     mkv->duration = FFMAX(mkv->duration, ts + duration);
     return 0;
 }
 
 static int mkv_copy_packet(MatroskaMuxContext *mkv, const AVPacket *pkt)
 {
     uint8_t *data           = mkv->cur_audio_pkt.data;
     mkv->cur_audio_pkt      = *pkt;
     mkv->cur_audio_pkt.data = av_fast_realloc(data, &mkv->audio_buffer_size, pkt->size);
     if (!mkv->cur_audio_pkt.data)
         return AVERROR(ENOMEM);
 
     memcpy(mkv->cur_audio_pkt.data, pkt->data, pkt->size);
     mkv->cur_audio_pkt.size = pkt->size;
     return 0;
 }
 
 static int mkv_write_packet(AVFormatContext *s, AVPacket *pkt)
 {
     MatroskaMuxContext *mkv = s->priv_data;

     AVIOContext *pb = s->pb->seekable ? s->pb : mkv->dyn_bc;

     AVCodecContext *codec = s->streams[pkt->stream_index]->codec;
     int ret, keyframe = !!(pkt->flags & AV_PKT_FLAG_KEY);

     int64_t ts;

     int cluster_size = avio_tell(pb) - (s->pb->seekable ? mkv->cluster_pos : 0);

     if (pkt->dts < 0 && !mkv->ts_offset)
         mkv->ts_offset = -pkt->dts;
 
     pkt->dts += mkv->ts_offset;
     if (pkt->pts != AV_NOPTS_VALUE)
         pkt->pts += mkv->ts_offset;
 
     ts = mkv->tracks[pkt->stream_index].write_dts ? pkt->dts : pkt->pts;
 

     // start a new cluster every 5 MB or 5 sec, or 32k / 1 sec for streaming or
     // after 4k and on a keyframe

     if (mkv->cluster_pos != -1 &&

         ((!s->pb->seekable && (cluster_size > 32*1024 || ts > mkv->cluster_pts + 1000))

          ||                      cluster_size > 5*1024*1024 || ts > mkv->cluster_pts + 5000
          || (codec->codec_type == AVMEDIA_TYPE_VIDEO && keyframe && cluster_size > 4*1024))) {

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

                " bytes, pts %" PRIu64 "\n", avio_tell(pb), ts);

         end_ebml_master(pb, mkv->cluster);

         mkv->cluster_pos = -1;

         if (mkv->dyn_bc)
             mkv_flush_dynbuf(s);

     }
 

     // check if we have an audio packet cached
     if (mkv->cur_audio_pkt.size > 0) {
         ret = mkv_write_packet_internal(s, &mkv->cur_audio_pkt);
         mkv->cur_audio_pkt.size = 0;
         if (ret < 0) {
             av_log(s, AV_LOG_ERROR, "Could not write cached audio packet ret:%d\n", ret);
             return ret;
         }
     }
 
     // buffer an audio packet to ensure the packet containing the video
     // keyframe's timecode is contained in the same cluster for WebM
     if (codec->codec_type == AVMEDIA_TYPE_AUDIO)
         ret = mkv_copy_packet(mkv, pkt);
     else
         ret = mkv_write_packet_internal(s, pkt);
     return ret;

 }
 
 static int mkv_write_trailer(AVFormatContext *s)
 {
     MatroskaMuxContext *mkv = s->priv_data;

     AVIOContext *pb = s->pb;

     int64_t currentpos, cuespos;

     int ret;

     // check if we have an audio packet cached
     if (mkv->cur_audio_pkt.size > 0) {
         ret = mkv_write_packet_internal(s, &mkv->cur_audio_pkt);
         mkv->cur_audio_pkt.size = 0;
         if (ret < 0) {
             av_log(s, AV_LOG_ERROR, "Could not write cached audio packet ret:%d\n", ret);
             return ret;
         }
     }
 

     if (mkv->dyn_bc) {
         end_ebml_master(mkv->dyn_bc, mkv->cluster);
         mkv_flush_dynbuf(s);

     } else if (mkv->cluster_pos != -1) {

         end_ebml_master(pb, mkv->cluster);
     }

     if (pb->seekable) {

         if (mkv->cues->num_entries) {
             cuespos = mkv_write_cues(pb, mkv->cues, s->nb_streams);
 
             ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_CUES, cuespos);
             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 = avio_tell(pb);

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

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

         avio_seek(pb, currentpos, SEEK_SET);

     }

     end_ebml_master(pb, mkv->segment);

     av_free(mkv->tracks);

     av_freep(&mkv->cues->entries);
     av_freep(&mkv->cues);

     av_destruct_packet(&mkv->cur_audio_pkt);

     return 0;
 }
 

 static int mkv_query_codec(enum AVCodecID codec_id, int std_compliance)

 {
     int i;

     for (i = 0; ff_mkv_codec_tags[i].id != AV_CODEC_ID_NONE; i++)

         if (ff_mkv_codec_tags[i].id == codec_id)
             return 1;
 
     if (std_compliance < FF_COMPLIANCE_NORMAL) {                // mkv theoretically supports any
         enum AVMediaType type = avcodec_get_type(codec_id);     // video/audio through VFW/ACM
         if (type == AVMEDIA_TYPE_VIDEO || type == AVMEDIA_TYPE_AUDIO)
             return 1;
     }
 
     return 0;
 }
 

 const AVCodecTag additional_audio_tags[] = {
     { AV_CODEC_ID_ALAC,      0XFFFFFFFF },
     { AV_CODEC_ID_EAC3,      0XFFFFFFFF },
     { AV_CODEC_ID_MLP,       0xFFFFFFFF },
     { AV_CODEC_ID_OPUS,      0xFFFFFFFF },
     { AV_CODEC_ID_PCM_S16BE, 0xFFFFFFFF },
     { AV_CODEC_ID_PCM_S24BE, 0xFFFFFFFF },
     { AV_CODEC_ID_PCM_S32BE, 0xFFFFFFFF },
     { AV_CODEC_ID_QDM2,      0xFFFFFFFF },
     { AV_CODEC_ID_RA_144,    0xFFFFFFFF },
     { AV_CODEC_ID_RA_288,    0xFFFFFFFF },
     { AV_CODEC_ID_COOK,      0xFFFFFFFF },
     { AV_CODEC_ID_TRUEHD,    0xFFFFFFFF },
     { AV_CODEC_ID_TTA,       0xFFFFFFFF },
     { AV_CODEC_ID_WAVPACK,   0xFFFFFFFF },
     { AV_CODEC_ID_NONE,      0xFFFFFFFF }
 };
 
 const AVCodecTag additional_video_tags[] = {
     { AV_CODEC_ID_RV10,      0xFFFFFFFF },
     { AV_CODEC_ID_RV20,      0xFFFFFFFF },
     { AV_CODEC_ID_RV30,      0xFFFFFFFF },
     { AV_CODEC_ID_RV40,      0xFFFFFFFF },
     { AV_CODEC_ID_NONE,      0xFFFFFFFF }
 };
 

 #if CONFIG_MATROSKA_MUXER

 AVOutputFormat ff_matroska_muxer = {

     .name              = "matroska",

     .long_name         = NULL_IF_CONFIG_SMALL("Matroska"),

     .mime_type         = "video/x-matroska",
     .extensions        = "mkv",
     .priv_data_size    = sizeof(MatroskaMuxContext),

     .audio_codec       = CONFIG_LIBVORBIS_ENCODER ?

                          AV_CODEC_ID_VORBIS : AV_CODEC_ID_AC3,

     .video_codec       = CONFIG_LIBX264_ENCODER ?

                          AV_CODEC_ID_H264 : AV_CODEC_ID_MPEG4,

     .write_header      = mkv_write_header,
     .write_packet      = mkv_write_packet,
     .write_trailer     = mkv_write_trailer,

     .flags             = AVFMT_GLOBALHEADER | AVFMT_VARIABLE_FPS |
                          AVFMT_TS_NONSTRICT,

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

     .subtitle_codec    = AV_CODEC_ID_SSA,

     .query_codec       = mkv_query_codec,

 };

 #endif
 
 #if CONFIG_WEBM_MUXER

 AVOutputFormat ff_webm_muxer = {

     .name              = "webm",

     .long_name         = NULL_IF_CONFIG_SMALL("WebM"),

     .mime_type         = "video/webm",
     .extensions        = "webm",
     .priv_data_size    = sizeof(MatroskaMuxContext),

     .audio_codec       = AV_CODEC_ID_VORBIS,
     .video_codec       = AV_CODEC_ID_VP8,

     .write_header      = mkv_write_header,
     .write_packet      = mkv_write_packet,
     .write_trailer     = mkv_write_trailer,

     .flags             = AVFMT_GLOBALHEADER | AVFMT_VARIABLE_FPS |
                          AVFMT_TS_NONSTRICT,

 };
 #endif

 #if CONFIG_MATROSKA_AUDIO_MUXER

 AVOutputFormat ff_matroska_audio_muxer = {

     .name              = "matroska",

     .long_name         = NULL_IF_CONFIG_SMALL("Matroska"),

     .mime_type         = "audio/x-matroska",
     .extensions        = "mka",
     .priv_data_size    = sizeof(MatroskaMuxContext),

     .audio_codec       = CONFIG_LIBVORBIS_ENCODER ?

                          AV_CODEC_ID_VORBIS : AV_CODEC_ID_AC3,
     .video_codec       = AV_CODEC_ID_NONE,

     .write_header      = mkv_write_header,
     .write_packet      = mkv_write_packet,
     .write_trailer     = mkv_write_trailer,

     .flags             = AVFMT_GLOBALHEADER | AVFMT_TS_NONSTRICT,

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

 };

 #endif