ffmpeg/libavformat/movenc_ttml.c

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/*
* MP4, ISMV Muxer TTML helpers
* Copyright (c) 2021 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
*/
#include "avformat.h"
#include "avio_internal.h"
#include "isom.h"
#include "movenc.h"
#include "movenc_ttml.h"
#include "libavcodec/packet_internal.h"
static const unsigned char empty_ttml_document[] =
"<tt xml:lang=\"\" xmlns=\"http://www.w3.org/ns/ttml\" />";
static int mov_init_ttml_writer(MOVTrack *track, AVFormatContext **out_ctx)
{
AVStream *movenc_stream = track->st, *ttml_stream = NULL;
int ret = AVERROR_BUG;
if ((ret = avformat_alloc_output_context2(out_ctx, NULL,
"ttml", NULL)) < 0)
return ret;
if ((ret = avio_open_dyn_buf(&(*out_ctx)->pb)) < 0)
return ret;
if (!(ttml_stream = avformat_new_stream(*out_ctx, NULL))) {
return AVERROR(ENOMEM);
}
if ((ret = avcodec_parameters_copy(ttml_stream->codecpar,
movenc_stream->codecpar)) < 0)
return ret;
ttml_stream->time_base = movenc_stream->time_base;
return 0;
}
static int mov_write_ttml_document_from_queue(AVFormatContext *s,
AVFormatContext *ttml_ctx,
MOVTrack *track,
AVPacket *pkt,
int64_t *out_start_ts,
int64_t *out_duration)
{
int ret = AVERROR_BUG;
int64_t start_ts = track->start_dts == AV_NOPTS_VALUE ?
0 : (track->start_dts + track->track_duration);
int64_t end_ts = start_ts;
if ((ret = avformat_write_header(ttml_ctx, NULL)) < 0) {
return ret;
}
while (!avpriv_packet_list_get(&track->squashed_packet_queue, pkt)) {
end_ts = FFMAX(end_ts, pkt->pts + pkt->duration);
// in case of the 'dfxp' muxing mode, each written document is offset
// to its containing sample's beginning.
if (track->par->codec_tag == MOV_ISMV_TTML_TAG) {
pkt->dts = pkt->pts = (pkt->pts - start_ts);
}
pkt->stream_index = 0;
av_packet_rescale_ts(pkt, track->st->time_base,
ttml_ctx->streams[pkt->stream_index]->time_base);
if ((ret = av_write_frame(ttml_ctx, pkt)) < 0) {
goto cleanup;
}
av_packet_unref(pkt);
}
if ((ret = av_write_trailer(ttml_ctx)) < 0)
goto cleanup;
*out_start_ts = start_ts;
*out_duration = end_ts - start_ts;
ret = 0;
cleanup:
return ret;
}
int ff_mov_generate_squashed_ttml_packet(AVFormatContext *s,
MOVTrack *track, AVPacket *pkt)
{
AVFormatContext *ttml_ctx = NULL;
// values for the generated AVPacket
int64_t start_ts = 0;
int64_t duration = 0;
int ret = AVERROR_BUG;
if ((ret = mov_init_ttml_writer(track, &ttml_ctx)) < 0) {
av_log(s, AV_LOG_ERROR, "Failed to initialize the TTML writer: %s\n",
av_err2str(ret));
goto cleanup;
}
if (!track->squashed_packet_queue.head) {
// empty queue, write minimal empty document with zero duration
avio_write(ttml_ctx->pb, empty_ttml_document,
sizeof(empty_ttml_document) - 1);
start_ts = 0;
duration = 0;
goto generate_packet;
}
if ((ret = mov_write_ttml_document_from_queue(s, ttml_ctx, track, pkt,
&start_ts,
&duration)) < 0) {
av_log(s, AV_LOG_ERROR,
"Failed to generate a squashed TTML packet from the packet "
"queue: %s\n",
av_err2str(ret));
goto cleanup;
}
generate_packet:
{
// Generate an AVPacket from the data written into the dynamic buffer.
uint8_t *buf = NULL;
int buf_len = avio_close_dyn_buf(ttml_ctx->pb, &buf);
ttml_ctx->pb = NULL;
if ((ret = av_packet_from_data(pkt, buf, buf_len)) < 0) {
av_log(s, AV_LOG_ERROR,
"Failed to create a TTML AVPacket from AVIO data: %s\n",
av_err2str(ret));
av_freep(&buf);
goto cleanup;
}
pkt->pts = pkt->dts = start_ts;
pkt->duration = duration;
pkt->flags |= AV_PKT_FLAG_KEY;
}
ret = 0;
cleanup:
if (ttml_ctx)
ffio_free_dyn_buf(&ttml_ctx->pb);
avformat_free_context(ttml_ctx);
return ret;
}