doxygen/4.4/libavformat_2ttmlenc_8c_source.html

/*

 * TTML subtitle muxer

 * Copyright (c) 2020 24i

 *

 * 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

 */


/**

 * @file

 * TTML subtitle muxer

 * @see https://www.w3.org/TR/ttml1/

 * @see https://www.w3.org/TR/ttml2/

 * @see https://www.w3.org/TR/ttml-imsc/rec

 */


#include "avformat.h"

#include "internal.h"

#include "libavcodec/ttmlenc.h"

#include "libavutil/internal.h"


enum TTMLPacketType {

    PACKET_TYPE_PARAGRAPH,

    PACKET_TYPE_DOCUMENT,

};


typedef struct TTMLMuxContext {

    enum TTMLPacketType input_type;

    unsigned int document_written;

} TTMLMuxContext;


static const char ttml_header_text[] =

"<?xml version=\"1.0\" encoding=\"utf-8\"?>\n"

"<tt\n"

"  xmlns=\"http://www.w3.org/ns/ttml\"\n"

"  xmlns:ttm=\"http://www.w3.org/ns/ttml#metadata\"\n"

"  xmlns:tts=\"http://www.w3.org/ns/ttml#styling\"\n"

"  xml:lang=\"%s\">\n"

"  <body>\n"

"    <div>\n";


static const char ttml_footer_text[] =

"    </div>\n"

"  </body>\n"

"</tt>\n";


static void ttml_write_time(AVIOContext *pb, const char tag[],

                            int64_t millisec)

{

    int64_t sec, min, hour;

    sec = millisec / 1000;

    millisec -= 1000 * sec;

    min = sec / 60;

    sec -= 60 * min;

    hour = min / 60;

    min -= 60 * hour;


    avio_printf(pb, "%s=\"%02"PRId64":%02"PRId64":%02"PRId64".%03"PRId64"\"",

                tag, hour, min, sec, millisec);

}


static int ttml_write_header(AVFormatContext *ctx)

{

    TTMLMuxContext *ttml_ctx = ctx->priv_data;

    ttml_ctx->document_written = 0;


    if (ctx->nb_streams != 1 ||

        ctx->streams[0]->codecpar->codec_id != AV_CODEC_ID_TTML) {

        av_log(ctx, AV_LOG_ERROR, "Exactly one TTML stream is required!\n");

        return AVERROR(EINVAL);

    }


    {

        AVStream    *st = ctx->streams[0];

        AVIOContext *pb = ctx->pb;


        AVDictionaryEntry *lang = av_dict_get(st->metadata, "language", NULL,

                                              0);

        const char *printed_lang = (lang && lang->value) ? lang->value : "";


        // Not perfect, but decide whether the packet is a document or not

        // by the existence of the lavc ttmlenc extradata.

        ttml_ctx->input_type = (st->codecpar->extradata &&

                                st->codecpar->extradata_size >= TTMLENC_EXTRADATA_SIGNATURE_SIZE &&

                                !memcmp(st->codecpar->extradata,

                                        TTMLENC_EXTRADATA_SIGNATURE,

                                        TTMLENC_EXTRADATA_SIGNATURE_SIZE)) ?

                               PACKET_TYPE_PARAGRAPH :

                               PACKET_TYPE_DOCUMENT;


        avpriv_set_pts_info(st, 64, 1, 1000);


        if (ttml_ctx->input_type == PACKET_TYPE_PARAGRAPH)

            avio_printf(pb, ttml_header_text, printed_lang);

    }


    return 0;

}


static int ttml_write_packet(AVFormatContext *ctx, AVPacket *pkt)

{

    TTMLMuxContext *ttml_ctx = ctx->priv_data;

    AVIOContext    *pb       = ctx->pb;


    switch (ttml_ctx->input_type) {

    case PACKET_TYPE_PARAGRAPH:

        // write out a paragraph element with the given contents.

        avio_printf(pb,     "      <p\n");

        ttml_write_time(pb, "        begin", pkt->pts);

        avio_w8(pb, '\n');

        ttml_write_time(pb, "        end",   pkt->pts + pkt->duration);

        avio_printf(pb, ">");

        avio_write(pb, pkt->data, pkt->size);

        avio_printf(pb, "</p>\n");

        break;

    case PACKET_TYPE_DOCUMENT:

        // dump the given document out as-is.

        if (ttml_ctx->document_written) {

            av_log(ctx, AV_LOG_ERROR,

                   "Attempting to write multiple TTML documents into a "

                   "single document! The XML specification forbids this "

                   "as there has to be a single root tag.\n");

            return AVERROR(EINVAL);

        }

        avio_write(pb, pkt->data, pkt->size);

        ttml_ctx->document_written = 1;

        break;

    default:

        av_log(ctx, AV_LOG_ERROR,

               "Internal error: invalid TTML input packet type: %d!\n",

               ttml_ctx->input_type);

        return AVERROR_BUG;

    }


    return 0;

}


static int ttml_write_trailer(AVFormatContext *ctx)

{

    TTMLMuxContext *ttml_ctx = ctx->priv_data;

    AVIOContext    *pb       = ctx->pb;


    if (ttml_ctx->input_type == PACKET_TYPE_PARAGRAPH)

        avio_printf(pb, ttml_footer_text);


    return 0;

}


AVOutputFormat ff_ttml_muxer = {

    .name              = "ttml",

    .long_name         = NULL_IF_CONFIG_SMALL("TTML subtitle"),

    .extensions        = "ttml",

    .mime_type         = "text/ttml",

    .priv_data_size    = sizeof(TTMLMuxContext),

    .flags             = AVFMT_GLOBALHEADER | AVFMT_VARIABLE_FPS |

                         AVFMT_TS_NONSTRICT,

    .subtitle_codec    = AV_CODEC_ID_TTML,

    .write_header      = ttml_write_header,

    .write_packet      = ttml_write_packet,

    .write_trailer     = ttml_write_trailer,

};