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MicroDVD files are normally frame-based (i.e. there are no absolute timestamps), but can have an optional frame rate header. If this header is missing, the timestamps depend on the frame rate of the video they were created for. The demuxer will use a fallback frame rate if it's missing from the header. Currently, applications using libavformat can't know whether the time base is based on the fallback value, or if a frame rate header was present. This commit introduces a subfps AVOption for MicroDVD, and the demuxer sets it if and only if a frame rate header was present. Signed-off-by: Clément Bœsch <u@pkh.me>
204 lines
6.2 KiB
C
204 lines
6.2 KiB
C
/*
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* MicroDVD subtitle demuxer
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* Copyright (c) 2010 Aurelien Jacobs <aurel@gnuage.org>
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* Copyright (c) 2012 Clément Bœsch <u pkh me>
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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 "subtitles.h"
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#include "libavutil/intreadwrite.h"
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#include "libavutil/opt.h"
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#define MAX_LINESIZE 2048
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typedef struct {
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const AVClass *class;
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FFDemuxSubtitlesQueue q;
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AVRational frame_rate;
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} MicroDVDContext;
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static int microdvd_probe(AVProbeData *p)
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{
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unsigned char c;
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const uint8_t *ptr = p->buf;
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int i;
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if (AV_RB24(ptr) == 0xEFBBBF)
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ptr += 3; /* skip UTF-8 BOM */
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for (i=0; i<3; i++) {
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if (sscanf(ptr, "{%*d}{}%c", &c) != 1 &&
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sscanf(ptr, "{%*d}{%*d}%c", &c) != 1 &&
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sscanf(ptr, "{DEFAULT}{}%c", &c) != 1)
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return 0;
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ptr += ff_subtitles_next_line(ptr);
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}
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return AVPROBE_SCORE_MAX;
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}
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static int64_t get_pts(const char *buf)
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{
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int frame;
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char c;
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if (sscanf(buf, "{%d}{%c", &frame, &c) == 2)
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return frame;
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return AV_NOPTS_VALUE;
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}
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static int get_duration(const char *buf)
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{
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int frame_start, frame_end;
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if (sscanf(buf, "{%d}{%d}", &frame_start, &frame_end) == 2)
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return frame_end - frame_start;
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return -1;
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}
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static const char *bom = "\xEF\xBB\xBF";
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static int microdvd_read_header(AVFormatContext *s)
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{
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AVRational pts_info = (AVRational){ 2997, 125 }; /* default: 23.976 fps */
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MicroDVDContext *microdvd = s->priv_data;
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AVStream *st = avformat_new_stream(s, NULL);
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int i = 0;
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char line_buf[MAX_LINESIZE];
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int has_real_fps = 0;
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if (!st)
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return AVERROR(ENOMEM);
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while (!url_feof(s->pb)) {
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char *p;
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AVPacket *sub;
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int64_t pos = avio_tell(s->pb);
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int len = ff_get_line(s->pb, line_buf, sizeof(line_buf));
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char *line = line_buf;
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if (!strncmp(line, bom, 3))
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line += 3;
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p = line;
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if (!len)
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break;
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line[strcspn(line, "\r\n")] = 0;
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if (i++ < 3) {
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int frame;
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double fps;
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char c;
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if ((sscanf(line, "{%d}{}%6lf", &frame, &fps) == 2 ||
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sscanf(line, "{%d}{%*d}%6lf", &frame, &fps) == 2)
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&& frame <= 1 && fps > 3 && fps < 100) {
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pts_info = av_d2q(fps, 100000);
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has_real_fps = 1;
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}
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if (!st->codec->extradata && sscanf(line, "{DEFAULT}{}%c", &c) == 1) {
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st->codec->extradata = av_strdup(line + 11);
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if (!st->codec->extradata)
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return AVERROR(ENOMEM);
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st->codec->extradata_size = strlen(st->codec->extradata) + 1;
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continue;
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}
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}
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#define SKIP_FRAME_ID \
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p = strchr(p, '}'); \
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if (!p) { \
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av_log(s, AV_LOG_WARNING, "Invalid event \"%s\"" \
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" at line %d\n", line, i); \
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continue; \
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} \
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p++
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SKIP_FRAME_ID;
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SKIP_FRAME_ID;
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if (!*p)
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continue;
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sub = ff_subtitles_queue_insert(µdvd->q, p, strlen(p), 0);
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if (!sub)
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return AVERROR(ENOMEM);
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sub->pos = pos;
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sub->pts = get_pts(line);
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sub->duration = get_duration(line);
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}
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ff_subtitles_queue_finalize(µdvd->q);
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if (has_real_fps) {
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/* export the FPS info only if set in the file */
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microdvd->frame_rate = pts_info;
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} else if (microdvd->frame_rate.num) {
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/* fallback on user specified frame rate */
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pts_info = microdvd->frame_rate;
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}
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avpriv_set_pts_info(st, 64, pts_info.den, pts_info.num);
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st->codec->codec_type = AVMEDIA_TYPE_SUBTITLE;
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st->codec->codec_id = AV_CODEC_ID_MICRODVD;
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return 0;
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}
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static int microdvd_read_packet(AVFormatContext *s, AVPacket *pkt)
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{
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MicroDVDContext *microdvd = s->priv_data;
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return ff_subtitles_queue_read_packet(µdvd->q, pkt);
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}
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static int microdvd_read_seek(AVFormatContext *s, int stream_index,
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int64_t min_ts, int64_t ts, int64_t max_ts, int flags)
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{
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MicroDVDContext *microdvd = s->priv_data;
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return ff_subtitles_queue_seek(µdvd->q, s, stream_index,
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min_ts, ts, max_ts, flags);
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}
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static int microdvd_read_close(AVFormatContext *s)
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{
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MicroDVDContext *microdvd = s->priv_data;
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ff_subtitles_queue_clean(µdvd->q);
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return 0;
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}
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#define OFFSET(x) offsetof(MicroDVDContext, x)
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#define SD AV_OPT_FLAG_SUBTITLE_PARAM|AV_OPT_FLAG_DECODING_PARAM
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static const AVOption microdvd_options[] = {
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{ "subfps", "set the movie frame rate fallback", OFFSET(frame_rate), AV_OPT_TYPE_RATIONAL, {.dbl=0}, 0, INT_MAX, SD },
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{ NULL }
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};
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static const AVClass microdvd_class = {
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.class_name = "microdvddec",
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.item_name = av_default_item_name,
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.option = microdvd_options,
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.version = LIBAVUTIL_VERSION_INT,
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};
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AVInputFormat ff_microdvd_demuxer = {
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.name = "microdvd",
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.long_name = NULL_IF_CONFIG_SMALL("MicroDVD subtitle format"),
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.priv_data_size = sizeof(MicroDVDContext),
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.read_probe = microdvd_probe,
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.read_header = microdvd_read_header,
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.read_packet = microdvd_read_packet,
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.read_seek2 = microdvd_read_seek,
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.read_close = microdvd_read_close,
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.priv_class = µdvd_class,
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};
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