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9d89c8b3ac
After much discussion and back-and-forth, we reached the conclusion that matroska uses convergence_duration for subtitle duration because a 32bit value isn't large enough to store the duration if sub-micro-second timebases are used. Matroska may not be the only one that supports these timebases, but it's certainly the only one that ffmpeg attempts to support in this way. The long term solution that we seemed to reach was that if we encounter a matroska file with a sub-micro-second timebase, we should internally scale it up to at least micro-second, and then duration can be used normally. This suggests that on the encode side, we should not allow generation of files with sub-micro-second timebases, but that's a separate issue. That being a non-trivial change, and the subtitle interoperability breakage being very real, I'm re-submitting this small change for consideration. In this diff, we make sure that duration is populated by the matroska demuxer, and that convergence_duration is respected in matroskaenc and srtenc, but that duration is used otherwise. This ends up being a strict improvement - pipelines that use convergence duration are unchanged, and ones that are currently broken due to the duration mismatch will start working - except for the ones with the extreme timebases, but those were already broken. Signed-off-by: Philip Langdale <philipl@overt.org>
102 lines
3.4 KiB
C
102 lines
3.4 KiB
C
/*
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* SubRip subtitle muxer
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* Copyright (c) 2012 Nicolas George <nicolas.george@normalesup.org>
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include "avformat.h"
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#include "internal.h"
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#include "libavutil/log.h"
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/* TODO: add options for:
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- character encoding;
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- LF / CRLF;
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- byte order mark.
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*/
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typedef struct SRTContext{
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unsigned index;
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} SRTContext;
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static int srt_write_header(AVFormatContext *avf)
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{
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if (avf->nb_streams != 1 ||
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avf->streams[0]->codec->codec_type != AVMEDIA_TYPE_SUBTITLE) {
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av_log(avf, AV_LOG_ERROR,
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"SRT supports only a single subtitles stream.\n");
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return AVERROR(EINVAL);
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}
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if (avf->streams[0]->codec->codec_id != AV_CODEC_ID_TEXT &&
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avf->streams[0]->codec->codec_id != AV_CODEC_ID_SUBRIP &&
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avf->streams[0]->codec->codec_id != AV_CODEC_ID_SRT) {
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av_log(avf, AV_LOG_ERROR,
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"Unsupported subtitles codec: %s\n",
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avcodec_get_name(avf->streams[0]->codec->codec_id));
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return AVERROR(EINVAL);
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}
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avpriv_set_pts_info(avf->streams[0], 64, 1, 1000);
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return 0;
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}
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static int srt_write_packet(AVFormatContext *avf, AVPacket *pkt)
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{
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SRTContext *srt = avf->priv_data;
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int write_ts = avf->streams[0]->codec->codec_id != AV_CODEC_ID_SRT;
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srt->index++;
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if (write_ts) {
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char buf[64];
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int64_t s = pkt->pts, e, d = pkt->duration;
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int len;
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if (d <= 0)
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/* For backward compatibility, fallback to convergence_duration. */
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d = pkt->convergence_duration;
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if (s == AV_NOPTS_VALUE || d <= 0) {
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av_log(avf, AV_LOG_ERROR, "Insufficient timestamps.\n");
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return AVERROR(EINVAL);
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}
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e = s + d;
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len = snprintf(buf, sizeof(buf),
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"%d\n%02d:%02d:%02d,%03d --> %02d:%02d:%02d,%03d\n",
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srt->index,
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(int)(s / 3600000), (int)(s / 60000) % 60,
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(int)(s / 1000) % 60, (int)(s % 1000),
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(int)(e / 3600000), (int)(e / 60000) % 60,
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(int)(e / 1000) % 60, (int)(e % 1000));
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avio_write(avf->pb, buf, len);
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}
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avio_write(avf->pb, pkt->data, pkt->size);
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if (write_ts)
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avio_write(avf->pb, "\n\n", 2);
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avio_flush(avf->pb);
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return 0;
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}
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AVOutputFormat ff_srt_muxer = {
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.name = "srt",
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.long_name = NULL_IF_CONFIG_SMALL("SubRip subtitle"),
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.mime_type = "application/x-subrip",
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.extensions = "srt",
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.priv_data_size = sizeof(SRTContext),
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.write_header = srt_write_header,
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.write_packet = srt_write_packet,
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.flags = AVFMT_VARIABLE_FPS,
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.subtitle_codec = AV_CODEC_ID_TEXT,
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};
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