FFmpeg/libavformat/srtdec.c

/*
 * SubRip subtitle demuxer
 * Copyright (c) 2010  Aurelien Jacobs <aurel@gnuage.org>
 *
 * 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 "internal.h"
#include "libavutil/bprint.h"
#include "libavutil/intreadwrite.h"

static int srt_probe(AVProbeData *p)
{
    unsigned char *ptr = p->buf;
    int i, v, num = 0;

    if (AV_RB24(ptr) == 0xEFBBBF)
        ptr += 3;  /* skip UTF-8 BOM */

    for (i=0; i<2; i++) {
        if ((num == i || num + 1 == i)
            && sscanf(ptr, "%*d:%*2d:%*2d%*1[,.]%*3d --> %*d:%*2d:%*2d%*1[,.]%3d", &v) == 1)
            return AVPROBE_SCORE_MAX;
        num = atoi(ptr);
        ptr += strcspn(ptr, "\n") + 1;
    }
    return 0;
}

static int srt_read_header(AVFormatContext *s)
{
    AVStream *st = avformat_new_stream(s, NULL);
    if (!st)
        return AVERROR(ENOMEM);
    avpriv_set_pts_info(st, 64, 1, 1000);
    st->codec->codec_type = AVMEDIA_TYPE_SUBTITLE;
    st->codec->codec_id   = AV_CODEC_ID_SUBRIP;
    return 0;
}

static int64_t get_pts(const char **buf, int *duration,
                       int32_t *x1, int32_t *y1, int32_t *x2, int32_t *y2)
{
    int i;

    for (i=0; i<2; i++) {
        int hh1, mm1, ss1, ms1;
        int hh2, mm2, ss2, ms2;
        if (sscanf(*buf, "%d:%2d:%2d%*1[,.]%3d --> %d:%2d:%2d%*1[,.]%3d"
                   "%*[ ]X1:%u X2:%u Y1:%u Y2:%u",
                   &hh1, &mm1, &ss1, &ms1,
                   &hh2, &mm2, &ss2, &ms2,
                   x1, x2, y1, y2) >= 8) {
            int64_t start = (hh1*3600LL + mm1*60LL + ss1) * 1000LL + ms1;
            int64_t end   = (hh2*3600LL + mm2*60LL + ss2) * 1000LL + ms2;
            *duration = end - start;
            *buf += strcspn(*buf, "\n") + 1;
            return start;
        }
        *buf += strcspn(*buf, "\n") + 1;
    }
    return AV_NOPTS_VALUE;
}

static inline int is_eol(char c)
{
    return c == '\r' || c == '\n';
}

static void read_chunk(AVIOContext *pb, AVBPrint *buf)
{
    char eol_buf[5];
    int n = 0, i = 0, nb_eol = 0;

    for (;;) {
        char c = avio_r8(pb);

        if (!c)
            break;

        /* ignore all initial line breaks */
        if (n == 0 && is_eol(c))
            continue;

        /* line break buffering: we don't want to add the trailing \r\n */
        if (is_eol(c)) {
            nb_eol += c == '\n';
            if (nb_eol == 2)
                break;
            eol_buf[i++] = c;
            if (i == sizeof(eol_buf) - 1)
                break;
            continue;
        }

        /* only one line break followed by data: we flush the line breaks
         * buffer */
        if (i) {
            eol_buf[i] = 0;
            av_bprintf(buf, "%s", eol_buf);
            i = nb_eol = 0;
        }

        av_bprint_chars(buf, c, 1);
        n++;
    }

    /* FIXME: remove the following when the lavc SubRip decoder is fixed
     * (trailing tags are not correctly flushed, see what happens to FATE when
     * you disable this code) */
    if (buf->len)
        av_bprintf(buf, "\n");
}

static int srt_read_packet(AVFormatContext *s, AVPacket *pkt)
{
    AVBPrint buf;
    int64_t pos = avio_tell(s->pb);
    int res = AVERROR_EOF;

    av_bprint_init(&buf, 0, AV_BPRINT_SIZE_UNLIMITED);
    read_chunk(s->pb, &buf);

    if (buf.len) {
        int64_t pts;
        int duration, pkt_size;
        const char *ptr = buf.str;
        int32_t x1 = -1, y1 = -1, x2 = -1, y2 = -1;

        pts = get_pts(&ptr, &duration, &x1, &y1, &x2, &y2);
        pkt_size = buf.len - (ptr - buf.str);
        if (pts != AV_NOPTS_VALUE && !(res = av_new_packet(pkt, pkt_size))) {
            memcpy(pkt->data, ptr, pkt->size);
            pkt->flags |= AV_PKT_FLAG_KEY;
            pkt->pos = pos;
            pkt->pts = pkt->dts = pts;
            pkt->duration = duration;
            if (x1 != -1) {
                uint8_t *p = av_packet_new_side_data(pkt, AV_PKT_DATA_SUBTITLE_POSITION, 16);
                if (p) {
                    AV_WL32(p,      x1);
                    AV_WL32(p +  4, y1);
                    AV_WL32(p +  8, x2);
                    AV_WL32(p + 12, y2);
                }
            }
        }
    }
    av_bprint_finalize(&buf, NULL);
    return res;
}

AVInputFormat ff_srt_demuxer = {
    .name        = "srt",
    .long_name   = NULL_IF_CONFIG_SMALL("SubRip subtitle"),
    .read_probe  = srt_probe,
    .read_header = srt_read_header,
    .read_packet = srt_read_packet,
    .flags       = AVFMT_GENERIC_INDEX,
};