ffmpeg/libavformat/ttmlenc.c

/*
 * 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 "libavutil/avstring.h"
#include "avformat.h"
#include "internal.h"
#include "ttmlenc.h"
#include "libavcodec/ttmlenc.h"
#include "libavutil/internal.h"

enum TTMLPacketType {
    PACKET_TYPE_PARAGRAPH,
    PACKET_TYPE_DOCUMENT,
};

struct TTMLHeaderParameters {
    const char *tt_element_params;
    const char *pre_body_elements;
};

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"
"%s"
"  xml:lang=\"%s\">\n"
"%s"
"  <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_set_header_values_from_extradata(
    AVCodecParameters *par, struct TTMLHeaderParameters *header_params)
{
    size_t additional_data_size =
        par->extradata_size - TTMLENC_EXTRADATA_SIGNATURE_SIZE;
    char *value =
        (char *)par->extradata + TTMLENC_EXTRADATA_SIGNATURE_SIZE;
    size_t value_size = av_strnlen(value, additional_data_size);
    struct TTMLHeaderParameters local_params = { 0 };

    if (!additional_data_size) {
        // simple case, we don't have to go through local_params and just
        // set default fall-back values (for old extradata format).
        header_params->tt_element_params = ttml_default_namespacing;
        header_params->pre_body_elements = "";

        return 0;
    }

    if (value_size == additional_data_size ||
        value[value_size] != '\0')
        return AVERROR_INVALIDDATA;

    local_params.tt_element_params = value;

    additional_data_size -= value_size + 1;
    value += value_size + 1;
    if (!additional_data_size)
        return AVERROR_INVALIDDATA;

    value_size = av_strnlen(value, additional_data_size);
    if (value_size == additional_data_size ||
        value[value_size] != '\0')
        return AVERROR_INVALIDDATA;

    local_params.pre_body_elements = value;

    *header_params = local_params;

    return 0;
}

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 : "";

        ttml_ctx->input_type = ff_is_ttml_stream_paragraph_based(st->codecpar) ?
                               PACKET_TYPE_PARAGRAPH :
                               PACKET_TYPE_DOCUMENT;

        avpriv_set_pts_info(st, 64, 1, 1000);

        if (ttml_ctx->input_type == PACKET_TYPE_PARAGRAPH) {
            struct TTMLHeaderParameters header_params;
            int ret = ttml_set_header_values_from_extradata(
                st->codecpar, &header_params);
            if (ret < 0) {
                av_log(ctx, AV_LOG_ERROR,
                       "Failed to parse TTML header values from extradata: "
                       "%s!\n", av_err2str(ret));
                return ret;
            }

            avio_printf(pb, ttml_header_text,
                        header_params.tt_element_params,
                        printed_lang,
                        header_params.pre_body_elements);
        }
    }

    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;
}

const 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,
};